User:Marshallsumter/Radiation astronomy/Earth

Earth is a rocky astronomical object, a liquid object, a gaseous object, and a plasma object.

Astronomy
At the right is a satellite composite image of the ice sheet over Greenland.

Radiation astronomy
"Energetic photons, ions and electrons from the solar wind, together with galactic and extragalactic cosmic rays, constantly bombard surfaces of planets, planetary satellites, dust particles, comets and asteroids." "[I]nterplanetary space ... is a stormy and sometimes very violent environment permeated by energetic particles and radiation constantly emanating from the Sun."

Planets
Def. "a celestial body that

(a) is in orbit around the Sun,

(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and

(c) has cleared the neighbourhood around its orbit" is called a planet.

The proposed more general definition for a planet in orbit around another star substitutes "a star" for "the Sun" in part (a), keeps part (b), does not contain part (c), and adds "is neither a star nor a satellite of a planet."

Theoretical Earth
Def. the "third planet in order from the Sun, upon which humans live" is called Earth.

Geognosy
The diagram on the right is a theoretical interior for the Earth. Some of the depths and likely constitution of successive spheres are based on the results of geoseismology.

Evidence from seismology, heat flow at the surface, and mineral physics is combined with the Earth's mass and moment of inertia to infer models of the Earth's interior - its composition, density, temperature, pressure. For example, the Earth's mean specific gravity (5.515) is far higher than the typical specific gravity of rocks at the surface (2.7–3.3), implying that the deeper material is denser. This is also implied by its low moment of inertia (0.33 M R2, compared to 0.4 M R2 for a sphere of constant density). However, some of the density increase is compression under the enormous pressures inside the Earth. The effect of pressure can be calculated using the Adams–Williamson equation. The conclusion is that pressure alone cannot account for the increase in density.

Reconstruction of seismic reflections in the deep interior indicate some major discontinuities in seismic velocities that demarcate the major zones of the Earth: inner core, outer core, mantle, lithosphere and crust.

The seismic model of the Earth does not by itself determine the composition of the layers. For a complete model of the Earth, mineral physics is needed to interpret seismic velocities in terms of composition. The mineral properties are temperature-dependent, so the geotherm must also be determined. This requires physical theory for thermal conduction and convection and the heat contribution of [radionuclides] radioactive elements. The main model for the radial structure of the interior of the Earth is the Preliminary Reference Earth Model (PREM). Some parts of this model have been updated by recent findings in mineral physics (see post-perovskite) and supplemented by seismic tomography.

Crusts
Using airborne astronomy, the image on the right shows a portion of the San Andreas Fault in California USA.

Cryospheres
The cryosphere is a term which collectively describes the portions of [an astronomical object's] surface where water is in solid form, including sea ice, lake ice, river ice, snow cover, glaciers, ice caps and ice sheets, and frozen ground (which includes permafrost). Thus there [may be] a wide overlap with [a] hydrosphere. The cryosphere is an integral part of the global climate system with important linkages and feedbacks generated through its influence on surface energy and moisture fluxes, clouds, precipitation, hydrology, atmospheric and oceanic circulation. Through these feedback processes, the cryosphere plays a significant role in global climate and in any climate model response to global change.

The only current ice sheets are in Antarctica and Greenland; during the last glacial period at Last Glacial Maximum (LGM) the Laurentide ice sheet covered much of North America, the Weichselian ice sheet covered northern Europe and the Patagonian Ice Sheet covered southern South America.

Lithospheres
Between the crust and the mantle is the Mohorovičić discontinuity.

Mantles
The mantle is mainly composed of silicates, and the boundaries between layers of the mantle are consistent with phase transitions.

The mantle acts as a solid for seismic waves, but under high pressures and temperatures it deforms so that over millions of years it acts like a liquid. This makes plate tectonics possible. Geodynamics is the study of the fluid flow in the mantle and core.

The mantle itself is divided into the upper mantle, transition zone, lower mantle and D′′ layer.

Outer cores
Reconstructions of seismic waves in the deep interior of the Earth show that there are no S-waves in the outer core. This indicates that the outer core is liquid, because liquids cannot support shear. The outer core is liquid, and the motion of this highly conductive fluid generates the Earth's field.

Inner cores
We know that the Earth's core is composed of an alloy of iron and other minerals.

"A PKJKP [P wave, traversing the outer core K, and the inner core J, to emerge again as the P wave] traverses the inner core as a shear wave, so this is the direct evidence that the inner core is solid, because only in the solid material the shear wave can exist. In the liquid material, say water, only the compressional wave can travel through."

Studying "archived data from about 20 large earthquakes, all monitored by an array of German seismic detectors back in the 1980s and '90s" has "reliably detected" a PKJKP wave in 2005, demonstrating that the inner core is solid.

The inner core, however, is solid because of the enormous pressure.

The inner core "is a solid ball of superhot iron and nickel alloy about 760 miles (1,220 kilometers) in diameter. ... the inner core is, at 10,800 degrees Fahrenheit (6,000 degrees Celsius), as hot as the surface of the sun."

"We know the Earth's inner core is composed mostly of iron".

"The metal [iron] was subjected to more than 200 billion pascals of pressure".

"[M]aterial within Earth's inner core is apparently distributed in a lopsided way ... The weakness of iron might lead crystallites in the inner core to flow and line up a certain way".

"[T]he speed at which the inner core spun apparently fluctuated over the course of approximately decades between 1961 and 2007."

"As the inner core cools, crystallizing iron releases impurities, sending lighter molten material into the liquid outer core. This upwelling, combined with the Earth's rotation, drives convection, forcing the molten metal into whirling vortices. These vortices stretch and twist magnetic field lines, creating Earth’s magnetic field. Currently, the center of the field, called an axis, emerges in the Arctic Ocean west of Ellesmere Island, about 300 miles (500 kilometers) from the geographic North Pole."

"In the last decade, seismic waves from earthquakes revealed the inner core looks like a navel orange, bulging slightly more on its western half. Geoscientists recently explained the asymmetry by proposing a convective loop: The inner core might be crystallizing on one half and melting on the other."

"The lopsided growth of the inner core makes convection in the outer core a little bit lopsided, and that then induces the geomagnetic field to have this lopsided or eccentric character too".

"Magnetic particles trapped and aligned in rocks reveal that the magnetic north pole wandered around the Western Hemisphere over the past 10,000 years, and circled the Eastern Hemisphere before that — a result mirrored by the numerical test."

"The key question for interesting ideas like translational instability is, 'Can we test it?' ... What we're doing is proposing a test, and we think it's a good test because people can go out and look for eccentricity in the rock record and that will either confirm or shoot down this idea."

"Within less than 100 million years, everything that has been crystallized on the west will have melted on the east"

Seismic "waves appear to travel faster through the inner core from north to south than from west to east. Seismic properties also seemed to vary between the Eastern and Western hemispheres of the globe."

There is a "124-mile (200-km) thick layer of dense material detected on its surface."

"[T]he inner core [may be] shifted slightly off-center, just to the east. This would put more pressure on the western side, where it would be closer to the center of the planet, and less pressure on the eastern side. The result could be a perpetually denser Western hemisphere and a continual flow of dense fluid from the east that eventually spreads out atop the entire inner core."

"The inner core is basically regenerating itself. And superimposed on that is this overall cooling that makes the inner core bigger and bigger over time".

"It is the first observational evidence that the inner core rotates at a variety of speeds with respect to the mantle...It also reconciles old discrepancies".

"The inner core, on average, rotates eastward. At the speeds it travels, it might, on average, complete a revolution every 750 to 1,440 years. However, these speeds appear unstable, which makes it uncertain just how long it actually takes to finish a turn on its axis".

Object astronomy
Def. "a body of unfrozen ground, that is perennially cryotic (T < 0 degrees Celsius) and entirely surrounded by perennially frozen ground" is called an isolated cryopeg.

Def. "a form of new ice, composed of spongy, white lumps a few cm across, that tend to form in rough seas; they resemble slushy snow balls" is called shuga.

Emissions
Def. a "process by which ice breaks off a glacier's terminus" is called calving.

Absorptions
"[P]referential absorption of sunlight by ozone over long horizon paths gives the zenith sky its blueness when the sun is near the horizon".

Def. a "bowl shape or amphitheater usually sculpted out of the mountain terrain by a ... glacier" is called a cirque.

The image at the right shows a cirque "on Cirque Mountain in the Torngat Mountains, Newfoundland, Canada."

Meteors
The Perseid meteor shower, a shower of rocks or rocky objects, usually the richest meteor shower of the year, peaks in August. Over the course of an hour, a person watching a clear sky from a dark location might see as many as 50-100 meteors. Most meteors are actually pieces of rock that have broken off a comet and continue to orbit the Sun. The Earth travels through the comet debris in its orbit. As the small pieces enter the Earth's atmosphere, friction can causes them to burn up.

The lower two images on the right show slower moving objects or clouds. These move relative to objects on the ground. By theoretical definition these are also meteors, but composed of water droplets small enough to be suspended in the Earth's atmosphere. They can move horizontally or can rise or form vertically as water vapor (a gas) condenses into small liquid drops of water.

The image on the left shows two meteors, the clouds passing over land and the rain falling towards the ground from the clouds above as the water droplets either lose their static charge or reach too large a size to be held aloft either by the natural electric field of the Earth or by air currents, respectively. The water droplets are moving somewhat horizontally and also vertically.

Def. a "part of a glacier with rapid flow and a chaotic crevassed surface; occurs where the glacier bed steepens or narrows" is called an icefall.

Def. "a rock that resides on a pedestal of ice; formed by differential ablation between the rock-covered ice and surrounding bare ice" is called a glacier table.

"Talefre Glacier on Mont Blanc Massif in the European Alps sported a prominent glacier table when this undated photograph was taken. The rock protected the ice directly below it from melting, resulting in the characteristic pedestal that remains after the surrounding ice melts. For scale, note the man standing behind and to the left of the pedestal."

When the glacier table top strikes the Earth with the melting of the pedestal, is the rock a meteorite?

Gamma rays
The Earth's atmosphere is a relatively bright source of gamma rays produced in interactions of ordinary cosmic ray protons with air atoms.

X-rays
The Earth is a known astronomical object. It is usually not thought of as an X-ray source.

At left is a composite image which contains the first picture of the Earth in X-rays, taken in March, 1996, with the orbiting Polar satellite. The area of brightest X-ray emission is red.

Energetic charged particles from the Sun energize electrons in the Earth's magnetosphere. These electrons move along the Earth's magnetic field and eventually strike the ionosphere, causing the X-ray emission.

"Beginning in 1995, a large outlet glacier of the Sermersauq Ice Cap on Disko Island [Greenland] surged 10.5 km downvalley to within 10 km of the head of the fjord, Kuannersuit Sulluat, reaching its maximum extent in summer 1999 before beginning to retreat. Sediment discharge to the fjord increased from 13 x 103 t day-1 in 1997 to 38 x 103 t day-1 in 1999. CTD results, sediment traps and cores from the 2000 melt season document the impact of the surge on the glacimarine environment of the fjord."

"Short gravity cores were taken and CTD profiles were recorded at stations throughout Kuannersuit Sulluat [...]. Positions located by GPS are accurate to ±10 m or less. The stream flowing over the sandur to the head of the fjord was gauged and integrated suspended sediment samples were recovered from primary channels."

"The cores were photographed, X-rayed and logged. X-radiographs provided measures of the number and size of gravel particles interpreted as ice-rafted debris (IRD) and the grey-scale (GS) of the scanned images was plotted as a measure of the properties of the sand and silt."

"The twelve layers in core D4 [imaged at the right] suggest a mean period of about 20 days for these events based on the accumulation rates in the traps [...]. In general, these layers have both higher MS and X-radiographs have lighter toned GS, the former related to lower water content and the latter also related to greater absorption of X-rays by the larger rock and mineral fragments."

There "are notable differences in the surge-generated sediments. The proximal sediments [such as in core D4 at the right] are more clearly laminated and layered in visual examination of the cores and as seen in the X-radiographs [compared to distal sediments as imaged on the left for core D20]. These consist both of the subtle differences in the fine-grained sediments on a millimetre scale, and of the sand layers up to 8 cm thick representing more energetic processes (Ó Cofaigh and Dowdeswell, 2001). Both are a response to greater sediment input to the fjord."

Opticals
"A NASA camera on the Deep Space Climate Observatory (DSCOVR) satellite has returned its first view of the entire sunlit side of Earth [on the right] from one million miles away."

"The color images of Earth from NASA’s Earth Polychromatic Imaging Camera (EPIC) are generated by combining three separate images to create a photographic-quality image. The camera takes a series of 10 images using different narrowband filters -- from ultraviolet to near infrared -- to produce a variety of science products. The red, green and blue channel images are used in these Earth images."

"This first DSCOVR image of our planet demonstrates the unique and important benefits of Earth observation from space. As a former astronaut who’s been privileged to view the Earth from orbit, I want everyone to be able to see and appreciate our planet as an integrated, interacting system. DSCOVR’s observations of Earth, as well as its measurements and early warnings of space weather events caused by the sun, will help every person to monitor the ever-changing Earth, and to understand how our planet fits into its neighborhood in the solar system.”

"These initial Earth images show the effects of sunlight scattered by air molecules, giving the images a characteristic bluish tint."

"The images clearly show desert sand structures, river systems and complex cloud patterns."

"The primary objective of DSCOVR, a partnership between NASA, the National Oceanic and Atmospheric Administration (NOAA) and the U.S. Air Force, is to maintain the nation’s real-time solar wind monitoring capabilities, which are critical to the accuracy and lead time of space weather alerts and forecasts from NOAA."

"In addition to space weather instruments, DSCOVR carries a second NASA sensor -- the National Institute of Science and Technology Advanced Radiometer (NISTAR)."

NASA's Earth Polychromatic Imaging Camera (EPIC) "is a four megapixel CCD camera and telescope. The color Earth images are created by combining three separate single-color images to create a photographic-quality imageequivalent to a 12-megapixel camera. The camera takes a series of 10 images using different narrowband filters -- from ultraviolet to near infrared -- to produce a variety of science products. The red, green and blue channel images are used to create the color images. Each image is about 3 megabytes in size."

"The effective resolution of the DSCOVR EPIC camera is somewhere between 6.2 and 9.4 miles (10 and 15 kilometers)."

"The visible reflectance declines from 0.95 to 0.60 as the snow cover metamorphoses to glacier ice [as seen in the figure at the left]."

"The Landsat-5 satellite, launched in March 1984, carries a Multispectral Scanner Subsystem (MSS) and a Thematic Mapper (TM) onboard. The TM senses in the following bands:"
 * 1) (TM1) 0.45-0.52 µm blue-cyan-green,
 * 2) (TM2) 0.52-0.60 µm green-yellow-orange,
 * 3) (TM3) 0.63-0.69 µm red,
 * 4) (TM4) 0.76-0.90 µm near-infrared,
 * 5) (TM5) 1.55-1.75 µm near-infrared,
 * 6) (TM6) 10.40-12.50 µm thermal infrared, and
 * 7) (TM7) 2.08-2.35 µm mid-infrared.

All "TM Bands 1-4 can be used to distinguish snow from firn and ice facies."

"The reflectance lies close to 0.6 for glacier ice and at about 0.2 for dirty glacier ice in the visible range, but increases a little in the infra-red due to the presence of moraine (Zeng et al. 1984). Thus, the visible TM Bands are suitable for separating dirty glacier ice from (clean) glacier ice whereas TM Band 4 is unsuited to this purpose. [...] glacier ice has a larger reflectance than refreezing ice in the visible region while the opposite is the case in the infra-red region."

Visuals
For those observers looking toward the Earth from another location such as near the Moon in the photograph at above right, it seems that the Earth is a natural object. On the Earth 384,000 km away, the sunset terminator bisects Africa.

A closer view of Earth shows some of the astronomical objects near the Earth and apparently just above the surface, where an observer may be. Some of these objects such as clouds probably by convention are more likely to be studied by planetary observers, or weather observers, rather than astronomical observers.

With perspectives other than upwards from the Earth's crustal surface, the word "sky" may seem insufficient or inappropriate, although studying the Earth as part of planetary science may leave interesting astronomical objects near the Earth that are occasionally "in the sky". The idea being that the Earth cannot be in its own sky, or can it? Perhaps, it is more a matter of whether other observers agree that what an observer is observing is astronomy or planetary science, or both.

"The search for life on extrasolar planets" requires a test of vegetation detectability from a single dot source.

"The earthshine, or ashen light, is the glow of the dark part of the lunar disk visible to a night-time observer. ... [T]he light rays coming from different parts of the Earth are mixed together in the ashen light and mimic the Earth as a single dot."

"[T]he vegetation spectrum which is unequivocal ... presents a bump at 0.5 µ in the green wavelength range, which implies that plants appear green".

Def. an "open fissure in the glacier surface" is called a crevasse.

The crevasse in the image at the right is in Lyman Glacier in 1916. The one on the left is in Langjökull glacier, Iceland, on 29 July 2006.

Violets
Def. "a large u-shaped valley formed from a v-shaped valley by glacial erosion" is called a glacial trough.

"The sheer walls of this glacial trough [Western Brook glacial trough, Newfoundland, Canada, at the right] soar up to 700 m high, and the glacial basin is 500 m deep in places."

Blues
Def. "[t]he gases surrounding the Earth or any astronomical body" is called an atmosphere.

Atmospheric gases scatter blue light more than other wavelengths, giving the Earth a blue halo when seen from space, as shown in the image at right.

Def. "ice that is anchored to the shore or ocean bottom, typically over shallow ocean shelves at continental margins; fast ice is defined by the fact that it does not move with the winds or currents" is called fast ice.

The image at the right shows land fast ice.

Cyans
"A digital elevation model (DEM) is a 3D representation of a terrain surface. DEMs are used in countless applications, such as hydrological/mass movement modeling or even 3D visualizations in flight simulators [...] for land-change studies [there] is [...] DEM differencing [...], which compares DEMs over the same region from different time periods [like the 3D image at the right over Bhutan]. This allows quantification of surface elevation changes due to erosion, landslides, earthquakes, melting glaciers, construction of man-made features, and many other factors. It follows that historical DEMs are useful for land-surface change studies."

To "reconstruct a DEM from 1974 imagery over a large glacierized region in the Bhutan Himalayas, [glacier] changes over several decades are visualized using a DEM differencing method."

"An implementation of the semi-global block matching algorithm (Hirschmuller, 2008) is utilized from the open source software package OpenCV to compute the stereo disparity map [imaged at the left]. Subsequently, matched pixels are projected back to their respective pre-rectified image coordinates using the inverse of the homography transformation."

"“Cool” pixels represent smaller disparities (valleys further from camera), while “hot” pixels represent larger disparities (mountains closer to camera)."

The image at the lower right is a Landsat panchromatic image of the study region in Bhutan/China, with an upper left inset of the Kingdom of Bhutan in red outline.

"Temporal changes in area and volume of glaciers and lakes are of interest in this region to better understand the effect of dwindling glacial ice on water resources."

Greens
Def. "perennial hummocks formed in either the active layer in permafrost areas, or in the seasonally frozen ground in non-permafrost areas, during freezing of the ground" is called thufur.

Yellows
In the photograph at the right, Piz Bernina is the highest mountain of the region. Note the yellow Sahara-dust layer melting out in the mid-elevation range of the glacier.

"The Morteratschgletscher is located in the Bernina Alps, in the Swiss province ("Kanton") Graubuenden, close to Sankt Moritz."

Oranges
Although limestone is usually light gray to white depending on impurities, the heavy glacial grooves and the limestone cross section in the image at the right are brown.

Reds
"Dusts originating from the Sahara/Sahel region are frequently spread over the Mediterranean Sea [Moulin et al., 1997], sometimes reaching France and even southern England [Bücher and Dessens, 1992]. These dusts can be easily sampled a few times a year in the French mountains – mostly in the Alps and the Pyrénées–where they suddenly cover snow surfaces with thin, red-to-brown blankets."

"Over the last 20 years, a few tens of red dust events suddenly covered snow surfaces in the Alps and Pyrénées mountains. They have been carefully sampled with plastic spatula and stored in clean bags [Grousset et al., 1994]. For each of those, the Nd isotopic composition of their carbonate-free fraction has been analyzed [Grousset et al., 1998]. The isotopic composition of Nd is usually defined by the 143Nd/144Nd ratio, which, for convenience, is normalized and reported as follows: ENd(o) = ((143Nd/144Nd/0.512636) − 1).104. Precision of the ENd(o) measurements is ≤ ± 0.2. In northern Africa, ENd(o) ranges from radiogenic values (ENd(o) ≈ 0) in young volcanic areas to unradiogenic values (ENd(o) ≈ −20) such as those observed in the Mauritania Archean provinces [Grousset et al., 1998]. When comparing the data obtained on the particles sampled in Alpine and Pyrenean snows, to those of the isotopic composition of the different dust fields of North Africa, it appears that the dusts reveal generally a North African origin."

Infrareds
The "Austre Brøggerbreen and Midre Lovénbreen glaciers [are] located 78°50'N, 11°50'E in the Svalbard archipelago. The satellite data are Landsat-5 TM images recorded on 7 August 1987 and 31 August 1988. In situ measurements of shortwave and spectral reflectance of snow, glacier ice and moraine were carried out in August 1991 and in June 1992."

The image at the right is a composite of visible reflectance in the green-yellow-orange (0.52-0.60 µm) and the infrared (0.76-0.90 µm and 1.55-1.75 µm).

"Austre Brøggerbreen (left arrow) and Midre Lovénbreen (right arrow) lie on the Brøggerhalvøya peninsula due south of the Kongsfjorden inlet. Austre Brøggerbreen terminates on land at about 75 [meters above sea level] m.a.s.l. The upper part of the glacier stretches up to 575 m.a.s.l. and the main flow direction is towards north i.e., towards the upper left corner of the image. The lower part of the glacier has low reflectance due to morainal deposits and exposed blue ice. A transition zone of superimposed ice is seen close to the arrow while the upper part is covered by snow."

"The near-infra-red snow albedo is sensitive to changes in characteristic snow grain size. Spectral measurements show a distinct drop in the near-infra-red albedo as the snow metamorphoses, i.e. the grain size increases. The visible albedo is little affected by the variation of grain size. Clouds affect the snow albedo by introducing a spectral shift to the incoming radiation. It is shown that the integrated snow albedo (370-900 nm) increases by 7% due to the change from clear sky to overcast weather."

Microwaves
"Active and passive microwave satellite data are used to map snowmelt extent and duration on the Greenland ice sheet. The passive microwave (PM) data reveal the extreme melt extent of 690,000 km2 in 2002 as compared with an average extent of 455,000 km2 from 1979–2003."

"Several PM-based melt assessment algorithms [Mote and Anderson, 1995; Abdalati and Steffen, 1995] are applicable to Scanning Multi-channel, Microwave Radiometer (SMMR) and Special Sensor Microwave/Imager (SSM/I) instruments providing near-continuous coverage since 1979. The PM data as gridded brightness temperatures on polar stereographic grids (25 km resolution) [used] are from the National Snow and Ice Data Center [Maslanik and Stroeve, 2003], containing daily data spanning 25 melt seasons from 1979 to 2003."

In the image at the right, (a) "shows the probabilities of the observed melt behavior on the Greenland ice sheet for several large melt years and indicates the extreme melt anomaly observed in northeastern Greenland in 2002."

"Prior to 2002, both 1995 and 1998 were extreme melt years in terms of maximum areal extent and total melt. During 1995 melt was dominated by a high frequency of melt along the western margin of the ice sheet. During 1998 melt was spatially diverse with slightly more melt than usual in the northeast and southwest. However, the high frequency melt in 2002 in the northeast and along the western margin is unprecedented in the PM record with a log likelihood of occurrence that is 35% lower than the previous record melt anomaly in 1991."

(c) "depicts the magnitude of the increasing trends in melt extent on a daily basis over the last 25 years. Although there is a large amount of inter-annual variability in melt extent on a given day, 56 days show statistically significant (alpha = 0.1) increasing trends in melt area."

"Melt along the west coast was extensive during 2002 but not atypical for large melt years. However melt in the north and northeast was highly irregular both in terms of extent and frequency. Nearly 3,000 km2[(b)] were classified as melting during 2002 that had not previously melted during any other year between 1979 and 2003."

The figure at the left "presents QSCAT backscatter and diurnal signatures, and ETH/CU AWS air temperature." Half-decade records for ETH/CU Camp station: (a) Top panel is for QSCAT backscatter, (b) middle panel for QSCAT diurnal signature, and (c) bottom panel for air temperature measured at the AWS site.

At the lower right QSCAT melt maps are shown on the climatological peak-melt day (1 August). Red color represents current active melt areas, light blue is for areas that have melted but currently refreeze, white is for areas that will melt later, and magenta is for areas that do not experience any melt throughout the melt season. The dark blue color surrounding Greenland is the ocean mask.

"QSCAT mapping can reveal details of the spatial pattern of surface melt evolution in time. There are large variabilities in melt extent and melt timing over different regions. [The figure at tje lower right] confirms that 2002 has the most extensive areal melt. In 2002, the northeast quadrant of the Greenland ice sheet, extending well into the dry snow zone, experienced at least some melt where melt never happened before (from satellite data records to date). Since the beginning of the QSCAT data record (July 1999), the smallest spatial extent of melt occurred in 2001, and melt extent was similar for years 2000 and 2003."

"To provide a direct comparison of PM and QSCAT results, we overlay results for PM melt extent and QSCAT number of melt days in [the figure at the lower left] for years 2000–2003. PM XPGR melt extent is approximately confined to QSCAT melt areas experiencing 2 weeks or more of melting time [the figure at the lower left]. QSCAT melt areas outside of the PM melt extent represent the surface that has less melt corresponding to about 15 melt days or less. This is consistent with the relationship of relative melt strength measured by active and passive data as discussed above. Note that such areas can total up to a large region in year 2002. Surface albedo can reduce considerably once the snow melts for a period of 2 weeks. The albedo reduction may significantly impact the surface heat balance and thus change the mass balance. The large number of melt days around the northern perimeter of the ice sheet, which is shown as the narrow dark-red band in north Greenland in the 2003 map was an anomalous feature [the figure at the lower left]. This band was wider as defined by the PM melt extent in 2002 than in 2003. However, there were more QSCAT melt days in the 2003 northern melt band."

"The comparison reveals that the PM cross-polarized gradient algorithm classifies melt more conservatively than the scatterometer algorithm. The active microwave identifies melt approximately up to two weeks more than the PM at higher elevation in the percolation zone toward the dry snow zone [the figure at the lower left]. Both methods (active and passive microwave) consistently identify melt areas that have a melt duration of at least 10–14 days. The longer snowmelt duration can be sufficient to decrease surface albedo and affect surface heat and mass balance."

Radars
Numerous airborne and spacecraft radars have mapped the entire planet, for various purposes. One example is the Shuttle Radar Topography Mission, which mapped the entire Earth at 30 m resolution.

Gaseous objects
"Methane trapped in a special type of permafrost [in the image at the right] is bubbling up at rate five times faster than originally measured [...]."

Liquid objects
Def. "water that forms transition layers at mineral/water and mineral/water/ice interfaces in frozen ground" is called interfacial water.

Def. "water occurring in unfrozen zones (taliks and cryopegs) within permafrost" is called interpermafrost water.

At the right is an "aerial view [of] thermokarst lakes outside the town of Chersky in northeast Siberia [on] August 28, 2007."

Def. "a lake occupying a closed depression formed by settlement of the ground following thawing of ice-rich permafrost or the melting of massive ice" is called a thermokarst lake.

"Paul Lake is located [...] at the border of Wisconsin and the upper peninsula of Michigan, USA [...] The center of the property is positioned at 46°13'N 89°32'E, with an altitude range between 500 and 520 m."

It "lies in [the] Northern Highland Province, which is the southernmost extension of the Canadian Shield. This province is characterized primarily by Pre-Cambrian bedrocks capped by a thin layer of sedimentary rocks left by the Paleozoic seas. On top of this formation are glacial deposits left by the Woodfordian and Valderan substages of the Wisconsinian glaciers. These glacial deposits are young and the drainage system is poorly developed. The surface deposits are characteristic of glacial retreat, consisting of infertile, sandy, pitted glacial out-wash or boulder and clay morainic deposits. As a result of their composition, the soils have a reduced capacity for cation exchange, leaving them very susceptible to acidification. Many of the lakes in this region are kettle lakes, others originate from irregular depressions in the ground moraine or were scoured out of the bedrock as the glaciers passed."

"Paul Lake has a surface area of 1 ha, a mean depth of 6 m, and a maximum depth of 13 m [...]. All the water entering Paul Lake comes from atmospheric deposition and groundwater seepage. Paul Lake generally remains stratified year-long because of a biogenic meromixis [...] and has been classified mesotrophic [...]. The concentration of soluble reactive phosphorus remains low in surface waters year-long, but nutrient regeneration at the oxic/anoxic transition promotes phyto-planktonic blooms just above this interface [...]."

Rocky objects
Sin-Kamen (Синь-Камень, in Russian literally – Blue Stone, or Blue Rock) is a type of pagan sacred stones, widespread in Russia, in areas historically inhabited by both Eastern Slavic (Russian), and Uralic tribes (Merya, Muroma ).

While in the majority of cases, the stones belonging to the Blue Stones type, have a black, or dark gray color, this particular stone [in the image] does indeed look dark blue, when wet.

Def. "a mass of rock fragments and finer material, on a slope, that contains either an ice core or interstitial ice, and shows evidence of past, but not present, movement" is called an inactive rock glacier.

Def. "a boulder swept from its place of origin by glacier advance or retreat and deposited elsewhere as the glacier melted; after glacial melt, the boulder might be stranded in a field or forest where no other rocks of its type or size exist" is called a glacial erratic.

"A sense of the size of the glacial erratic [imaged at the right in northeastern Manitoba, Canada]] can be estimated by noting the person standing in front of the boulder, on the left side. This erratic, as well as neighboring ones, were carried by the Keewatian Ice Sheet."

Astrochemistry
Def. a "type of Pleistocene-age (formed 1.8 million to 10,000 years before present) permafrost that contains a significant amount of organic material with ice content of 50-90% by volume" is called yedoma.

In the image at the right, a yedoma in Russia is a thick layer of ice and carbon material exposed along this body of water. "Thawing yedoma is a significant source of atmospheric methane."

Carbons
At the right is an image of yedoma.

"The shiny surface of the cliff represents massive ice wedges."

"Most of the yedoma is in little-studied areas of northern and eastern Siberia. What makes that permafrost special is that much of it lies under lakes; the carbon below gets released as methane. Carbon beneath dry permafrost is released as carbon dioxide."

"The big methane or carbon dioxide release hasn’t started yet, but it’s coming."

In the image at the right, "Sergey Zimov, director of the Northeast Science Station in Siberia, [examines] a cross-section of yedoma, carbon trapped in permafrost along the bank of the Kolyma River in Siberia."

"The dark sections in between are soil inclusions which contain ice-age organic carbon, left over from the Pleistocene steppe-tundra ecosystem."

Aluminums
"As Andean glaciers recede, there has been an increase in seasonal discharge and in catchments with the least glacierized area and a decrease in total annual discharge [...] Dry season examinations, including this study, are particularly important because during this period glacial melt provides up to 40% of the total discharge in the Cordillera Blanca (Mark et al., 2005). The dry season thus provides the greatest potential opportunity to evaluate water quality deterioration related to glacial retreat. [...] In the Cordillera Blanca, the exposure of fresh sulfide-rich lithologies by retreating glaciers (Wilson et al., 1967) is thus integral to the biogeochemistry of proglacial streams. [...] the dry season geochemistry of trace and minor elements was examined in the proglacial Rio Quilcay from within 1 km of its glacier origins to 12 km downstream."

The "Rio Quilcay [is] a glacial-fed tributary to the Upper Rio Santa in the uppermost 12 km at elevations ranging from approximately 4800 to ~3800 m.a.s.l. [...] The sampled region of the Rio Quilcay receives glacial melt directly and indirectly from two proglacial lakes: Cuchillacocha and Tulpacocha. Geology in this region of the Cordillera Blanca includes pyrite schists and phyllite and pyrite-bearing quartzite intruded by a central granodiorite-tonalite batholith all overlain by clastic sediments deposited during glacial retreat (Wilson et al., 1967). Sulfide-rich lithologies are prevalent especially in the north-eastern high-altitude regions of the Cordillera Blanca (e.g. the Rio Quilcay Valley) with fresh exposures resulting from glacial scour (Wilson et al., 1967). Many headwaters in the Cordillera Blanca, including the Rio Quilcay and its tributaries, have ochreous precipitates"

"Aluminum, Ca, Fe, K, Mn, Na, and Si were determined using an Optima 3000 DV Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES) using five calibration standards that bracketed the range of concentrations within the samples, excepting the three highest samples which were diluted 1:10 before analyses. Cobalt, Cu, Ni, Pb and Zn were determined on a Perkin–Elmer Sciex Elan 6000Ⓡ Inductively Coupled Plasma-Mass Spectromenter (ICP-MS) also using five calibration standards, however with no sample dilution. All element results were drift corrected. Sulfate and NO3- were determined using a Dionex DX-120 ion chromatograph (IC). Only SO42- is reported because other anions fall near detections limits (DLs) in the higher elevation samples, or represent less than 5% of the charge balance in the pH < 4 streams."

It "is likely that both the sulfide-rich lithology underlying the Rio Quilcay and the near-glacier sample locations enhanced sulfide weathering, and generated exceptionally high cation loads."

"Elevated dissolved Al, Fe and Cu concentrations (6.1mg/L, 21.4 mg/L, 6.1 lg/L) were observed at site 11, 0.3 km immediately downstream of a moraine. Concentrations of these elements increased by more than four times the concentrations at site 10. Concentration gains were likely associated with glacier melt rapidly weathering minerals within the moraine (Brown, 2002)."

"Tributary C also influenced the chemical composition of the stream immediately below its inflow at site 13. In fact, Fe reached the second highest concentration reported (12.8 mg/L) and dissolved Al, Mn, Co, Cu, Ni and Zn concentrations also increased above their upstream values. Tributary C overlays a region with enhanced sulfide mineral oxidation [image at the right]. Evidence for this includes a major cation: SO42- equivalent ratio of 1, and abundant algal mats covered with yellow and orange precipitates (Bigham et al., 1996). In addition, dissolved Al and Zn increased an additional 270% and 160% relative to site 13–14, respectively, and after the inflow of tributary D."

Cobalts
"On glacier surfaces conditions [...] exist for aerosols and airborne dust deposited with anthropogenic and natural radionuclides attached on their surfaces. In the course of agglomeration processes initiated by melting and redistribution, these particles may concentrate in small depressions, ice pockets, ablation edges etc. and form substances called cryoconites ('ice dust'). As there is no other matrix than the original aerosol particles, cryoconites are a sink for radionuclides and airborne pollutants and their activity levels are among the highest produced by natural processes observed in environmental media. 137Cs activities found on glaciers in the Austrian alps are between 255 and 136.000 Bq/kg and predominantly derived from Chernobyl, but also from global fallout. Further anthropogenic radionuclides detected are 134Cs, 90Sr, 238,239+240Pu, 241Am, 125Sb, 154Eu, 60Co and 207Bi [in] combination with the naturally occurring radionuclides 7Be and 210Pb and isotopic ratios such as 134Cs/137Cs".

The "concentration of dissolved Mn and Co [figure at the right] increase sharply across the oxic/anoxic transition, from 5 to 5.5 m depth. The concentration of Co rises from detection limit, when O2 is still present, to 6.8 nM and 12 nM, respectively, for May 1994 and July-August 1995."

In the oxic mixolimnion, dissolved Co remains primarily under its free hydrated form (Co[H2]2+6, whereas in the anoxic bottom waters it seems to be primarily present as a sulfide complex (CoS0).

Coppers
"Approximately five million tonnes were mined from native copper deposits in Michigan. Copper masses from the Michigan deposits were transported by the Pleistocene glaciers. Areas on the copper surfaces which appear to represent glacial abrasion show minimal corrosion."

"A group of pixel areas north of Lake Superior [in the Landsat image on the right] take the form of a linear band which lies along the northern edge of the Port Coldwell Complex (D). [...] there are numerous Cu showings along the northern edge of the Port Coldwell complex (Ontario Division of Mines, 1971)."

Compounds
The diagram at the right describes how methane (CH4) leaks from sea beds.

"Methane is far more powerful in trapping heat, but only lasts about a decade before it dissipates into carbon dioxide and other chemicals. Carbon dioxide traps heat for about a century."

Meteorites
Def. "[a] metallic or stony object that is the remains of a meteor", from Wiktionary meteorite, is called a meteorite.

Many of the meteorites that are found on Earth turn out to be from other solar system objects: the Moon and Mars, for example.

Widmanstätten patterns, also called Thomson structures, are unique figures of long nickel-iron crystals, found in the octahedrite iron meteorites and some pallasites. They consist of a fine interleaving of kamacite and taenite bands or ribbons called lamellæ. Commonly, in gaps between the lamellæ, a fine-grained mixture of kamacite and taenite called plessite can be found.

Def. a "mass of snow which becomes detached and slides down a slope, often acquiring great bulk by fresh addition as it descends" is called an avalanche.

Micrometeorites
Micrometeorite is often abbreviated as MM. Most MMs are broadly chondritic in composition, meaning "that major elemental abundance ratios are within about 50% of those observed in carbonaceous chondrites." Some MMs are chondrites, (basaltic) howardite, eucrite, and diogenite (HED) meteorites or Martian basalts, but not lunar samples. "[T]he comparative mechanical weakness of carbonaceous precursor materials tends to encourage spherule formation." From the number of different asteroidal precursors, the approximate fraction in MMs is 70 % carbonaceous. "[T]he carbonaceous material [is] known from observation to dominate the terrestrial MM flux." The "H, L, and E chondritic compositions" are "dominant among meteorites but rare among micrometeorites."

"Ureilites occur about half as often as eucrites (Krot et al. 2003), are relatively friable, have less a wide range of cosmic-ray exposure ages including two less than 1 Myr, and, like the dominant group of MM precursors, contain carbon."

Atmospheric astronomy
These molecules in many instances are in turn made up of atoms of chemical elements. At your geographical location, specified in latitude and longitude, this gaseous envelope extends upward. The atmosphere of Earth changes with altitude. At high enough altitude the composition changes significantly, as does the temperature and pressure.

The Earth's atmosphere is divided into altitude regions:
 * Troposphere &mdash; surface to 8,000 m at the poles – 18,000 m at the equator, ending at the Tropopause.
 * Stratosphere &mdash; Troposphere to 50 km
 * Mesosphere &mdash; Stratosphere to 85 km
 * Thermosphere &mdash; Mesosphere to 675 km
 * Exosphere &mdash; Thermosphere to 10,000 km, after altitude regions.

Ionospheres
Upon reaching the top of the mesosphere, the temperature starts to rise, but air pressure continues to fall. This is the beginning of the ionosphere, a region dominated by chemical ions. Many of them are the same chemicals such as nitrogen and oxygen in the atmosphere below, but an ever increasing number are hydrogen ions (protons) and helium ions. These can be detected by an ion spectrometer. The process of ionization removes one or more electrons from a neutral atom to yield a variety of ions depending on the chemical element species and incidence of sufficient energy to remove the electrons.

Exospheres
Into the exosphere or outer space, temperature rises from around 1,500°C to upwards of 100,000 K.

Sun
The Sun passes overhead every day on Earth. The size of its disc is very close to that of the Moon.

Regarding the fixed stars, the Sun appears from Earth to revolve once a year along the ecliptic through the zodiac, and so Greek astronomers considered it to be one of the seven planets (Greek planetes, "wanderer"), after which the seven days of the week are named in some languages.

"And Helios, lord of the sun, sitting Away from the other gods, sitting in his own temple And listening to prayers breathing up from men: he heard."

"[A]stronomically, the visible Helios occupies the central position among the seven planets - Kronos, Zeus, Ares, Helios, Aphrodite, Hermes, and Selene, in a descending series."

Skies
Being outside in the day light to look upward when the Sun is off to the East or West, you may see that the sky is blue depending on the weather.

There are many other natural objects, entities, bodies, or phenomena that occur in the sky. Some of these may occur frequently: the Sun passes overhead every day, so does the Moon either during the day or at night, a variety of clouds pass across the sky and sometimes completely fill the sky for days, occasionally a few go in the opposite direction across the sky or in different directions.

Def. "the expanse of space that seems to be over the earth like a dome" is called the sky, or the sometimes the heavens.

This definition applies especially well to an individual on top of the Earth's solid crust looking around at what lies above and off to the horizon in all directions. Similarly, it applies to an individual's visual view while floating on a large body of water, where off on the horizon is still water.

The image at right shows the horizon marking the lower edge of the sky and the upper edge of the Atlantic Ocean, with a layer of cumulus clouds just above.

Def. an "expanse of space that seems to be [overhead] like a dome" is called a sky.

Even in day light, the sky may seem absent of objects if a nearby source tends to overwhelm other luminous objects.

Volcanoes
Oblique images such as the one at right are taken by astronauts looking out from the ISS at an angle, rather than looking straight downward toward the Earth (a perspective called a nadir view), as is common with most remotely sensed data from satellites. An oblique view gives the scene a more three-dimension quality, and provides a look at the vertical structure of the volcanic plume. While much of the island is covered in green vegetation, grey deposits that include pyroclastic flows and volcanic mud-flows (lahars) are visible extending from the volcano toward the coastline. When compared to its extent in earlier views, the volcanic debris has filled in more of the eastern coastline. Urban areas are visible in the northern and western portions of the island; they are recognizable by linear street patterns and the presence of bright building rooftops. The silver-grey appearance of the Caribbean Sea surface is due to sun-glint, which is the mirror-like reflection of sunlight off the water surface back towards the hand-held camera on-board the ISS. The sun-glint highlights surface wave patterns around the island.

Craters
Occasionally, objects fall from the sky. When and where this occurs, depending on the energy dumped into the atmosphere and the impact on the crust of the Earth, life forms nearby hear it, feel the vibrations from it, and recoil if the intensity is too high.

But asteroid impacts, though rare, occur once in a while, over very large areas, at aperiodic intervals such as the Chicxulub crater. Most scientists agree that this impact is the cause of the Cretatious-Tertiary Extinction, 65 million years ago (Ma), that marked the sudden extinction of the dinosaurs and the majority of life then on Earth. This shaded relief image of Mexico's Yucatan Peninsula shows a subtle, but unmistakable, indication of the Chicxulub impact crater.

In the image at left is an aerial view of the Barringer Meteor Crater about 69 km east of Flagstaff, Arizona USA. Although similar to the aerial view of the Soudan crater, the Barringer Meteor Crater appears angular at the farthest ends rather than round.


 * Buried craters can be identified through drill coring, aerial electromagnetic resistivity imaging, and airborne gravity gradiometry.

At right is a "[r]ecent airborne geophysical surveys near Decorah, Iowa [which is] providing an unprecedented look at a 470- million-year-old meteorite crater concealed beneath bedrock and sediments."

"Capturing images of an ancient meteorite impact was a huge bonus," said Dr. Paul Bedrosian, a USGS geophysicist in Denver who is leading the effort to model the recently acquired geophysical data. "These findings highlight the range of applications that these geophysical methods can address."

"In 2008-09, geologists from the Iowa Department of Natural Resources' (Iowa DNR) Iowa Geological and Water Survey hypothesized what has become known as the Decorah Impact Structure. The scientists examined water well drill-cuttings and recognized a unique shale unit preserved only beneath and near the city of Decorah. The extent of the shale, which was deposited after the impact by an ancient seaway, defines a "nice circular basin" of 5.5 km width, according to Robert McKay, a geologist at the Iowa Geological Survey."

"Bevan French, a scientist the Smithsonian's National Museum of Natural History, subsequently identified shocked quartz - considered strong evidence of an extra-terrestrial impact - in samples of sub-shale breccia from within the crater."

"The recent geophysical surveys include an airborne electromagnetic system, which is sensitive to how well rocks conduct electricity, and airborne gravity gradiometry, which measures subtle changes in rock density. The surveys both confirm the earlier work and provide a new view of the Decorah Impact Structure. Models of the electromagnetic data show a crater filled with electrically conductive shale and the underlying breccia, which is rock composed of broken fragments of rock cemented together by a fine-grained matrix."

"The shale is an ideal target and provides the electrical contrast that allows us to clearly image the geometry and internal structure of the crater," Bedrosian said.

Tides
In addition to the Sun, the Moon affects life forms on Earth such as those along the shores of bodies of water through the production of tides.

"Due to phenomena such as ice ages, plate tectonics, land uplift, erosion and sedimentation, tides have changed dramatically over thousands of years".

"Some tides on the East Coast of the United States ... may ... have [had] ... a difference between low and high tide of 10-20 feet, instead of the current 3-6 foot range."

The Guinness Book of World Records (1975) declared that Burntcoat Head, Nova Scotia has the highest tides in the world: “The greatest tides in the world occur in the Bay of Fundy.... Burntcoat Head in the Minas Basin, Nova Scotia, has the greatest mean spring range with 14.5 metres (47.5 feet) and an extreme range of 16.3 metres (53.5 feet).”

But they "didn’t amount to much at all about 5,000 years ago. ... [A]round that same time, tides on the southern U.S. Atlantic coast, from North Carolina to Florida, were about 75 percent higher."

"[A]round 9,000 years ago ... there was a huge amplification in tides of the western Atlantic Ocean. The tidal ranges were up to three times more extreme than those that exist today, and water would have surged up and down on the East Coast."

Today Hudson Bay is a place "where tidal energy gets dissipated at a disproportionately high rate ... But during the last ice age Hudson Bay was closed down and buried in ice, and that caused more extreme tides elsewhere."

Auroras
Computer simulations are usually used to represent auroras. The image at right shows a terrella in a laboratory experiment to produce auroras.

"Although auroras might first appear to be moonlit clouds, they only add light to the sky and do not block background stars from view. Called "Northern Lights" in the Northern Hemisphere, auroras are caused by collisions between charged particles from the magnetosphere and air molecules high in the Earth's atmosphere. If viewed from space, auroras can be seen to glow in X-ray and ultraviolet light as well. Predictable auroras might occur a few days after a powerful magnetic event has been seen on the sun."

Most aurorae occur in a band known as the auroral zone, which is typically 3° to 6° in latitudinal extent and at all local times or longitudes. The auroral zone is typically 10° to 20° from the magnetic pole defined by the axis of the Earth's magnetic dipole. During a geomagnetic storm, the auroral zone will expand to lower latitudes. The diffuse aurora is a featureless glow in the sky which may not be visible to the naked eye even on a dark night and defines the extent of the auroral zone. The discrete aurora are sharply defined features within the diffuse aurora which vary in brightness from just barely visible to the naked eye to bright enough to read a newspaper at night. Discrete aurorae are usually observed only in the night sky because they are as bright as the sunlit sky. Aurorae occasionally occur poleward of the auroral zone as diffuse patches or arcs (polar cap arcs ), which are generally invisible to the naked eye.

Natural electric fields
On Earth, between the surface and various altitudes there is an electric field. It changes with altitude from about 150 volts per meter to lower values at higher altitude. In fair weather, it is relatively constant, in turbulent weather it is accompanied by ions. At greater altitude these chemical species continue to increase in concentration.

Usually when clouds fill the sky and associated with some of these clouds is lightning, a phenomenon that moves so quickly it’s difficult to think of it as an object or entity with a body.

"A number of observations by space-based telescopes have revealed ... gamma ray emissions ... terrestrial gamma-ray flashes (TGFs). These observations pose a challenge to current theories of lightning, especially with the discovery of the clear signatures of antimatter produced in lightning.

A TGF has been linked to an individual lightning stroke occurring within 1.5 ms of the TGF event, proving for the first time that the TGF was of atmospheric origin and associated with lightning strikes.

The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft, as reported by David Smith of UC Santa Cruz, has been observing TGFs at a much higher rate, indicating that these occur about 50 times per day globally (still a very small fraction of the total lightning on the planet). The energy levels recorded exceed 20 MeV. Apparently, the gamma radiation fountains upward from starting points at surprisingly low altitudes in thunderclouds. Steven Cummer, from Duke University's Pratt School of Engineering, said, "These are higher energy gamma rays than come from the sun. And yet here they are coming from the kind of terrestrial thunderstorm that we see here all the time." In 2009, the Fermi Gamma Ray Telescope in Earth orbit observed an intense burst of gamma rays corresponding to positron annihilations coming out of a storm formation. Scientists wouldn't have been surprised to see a few positrons accompanying any intense gamma ray burst, but the lightning flash detected by Fermi appeared to have produced about 100 trillion positrons. This has been reported by media in January 2011, it is an effect, never considered to happen before.

Zodiacal Light
"According to Gruson and Brugsch the Egyptians were acquainted with, and even worshipped, the zodiacal light from the very earliest times, as a phenomenon visible throughout the East before sunrise and after sunset. It was described as a glowing sheaf or luminous pyramid perpendicular to the horizon in summer, and inclined more or less during the winter. Indeed the Egyptians represented the zodiacal light under the form of a triangle which sometimes stood upright and at other times was inclined."

Tephra layers
An ashfall occurs from a nearby volcano, before the locals can leave the area or maybe even go to work.

Foliation
Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. It is the finest grained foliated metamorphic rock. Foliation may not correspond to the original sedimentary layering, but instead is in planes perpendicular to the direction of metamorphic compression. Slate is frequently grey in color, especially when seen, en masse, covering roofs. However, slate occurs in a variety of colors even from a single locality; for example, slate from North Wales can be found in many shades of grey, from pale to dark, and may also be purple, green or cyan.

Glaciology
Def. "a mass of ice that originates on land, usually having an area larger than one tenth of a square kilometer" is called a glacier.

"[M]any believe that a glacier must show some type of movement; others believe that a glacier can show evidence of past or present movement."

"Taku Glacier [in the image at the left] winds through the mountains of southeastern Alaska, calving small icebergs into Taku Inlet."

Def. the study of the internal dynamics and effects of glaciers is called glaciology.

"Satellite imagery and data from ground surveys are used to reconstruct the integrated pattern of the principal longitudinal and transverse features produced on a continent-wide scale by the last ice sheets in Europe and North America."

Def. "a dome-shaped mass of glacier ice that spreads out in all directions" is called an ice cap.

An "ice cap is usually larger than an icefield but less than 50,000 square-kilometers (12 million acres)."

Def. "a mass of glacier ice; similar to an ice cap, and usually smaller and lacking a dome-like shape; somewhat controlled by terrain" is called an icefield.

The image at the left of "Kalstenius Icefield, located on Ellesmere Island, Canada, shows vast stretches of ice. The icefield produces multiple outlet glaciers that flow into a larger valley glacier. The glacier in this photograph is three miles wide."

Astroglaciology
The discoveries of water ice on the Moon, Mars and Europa add an extraterrestrial component to the field, as in "astroglaciology".

Glaciers
Def. a "large ice lobe spread out over surrounding terrain, associated with the terminus of a large mountain valley glacier" is called a piedmont glacier.

"The massive lobe of Malaspina Glacier in Alaska is clearly visible in this photograph taken from a Space Shuttle flight in 1989. Agassiz Glacier is the smaller glacier to the left. The Malaspina Glacier is one of the most famous examples of this type of glacier, and is the largest piedmont glacier in the world. Spilling out of the Seward Ice Field (visible near the top of the photograph), it covers over 5,000 square kilometers as it spreads across the coastal plain."

Def. a "glacier that has one or more tributary glaciers that flow into it" is called a branched-valley glacier.

"In this photograph from 1969 [at the right], small glaciers flow into the larger Columbia Glacier from mountain valleys on both sides. Columbia Glacier flows out of the Chugach Mountains into Columbia Bay, Alaska."

Def. "a line drawn through geographical points recording equal amounts of precipitation during a specific period" is called an isohyet.

Def. a "mountain glacier that terminates in the ocean" is called a tidewater glacier.

Asteroids
"From the dominant group, the asteroids evolve to intersect the Earth's orbit on a median time scale of about 60 Myr."

EC denotes Earth-crossing.

"50 % of the MB Mars-crossers [MCs] become ECs within 59.9 Myr and [this] contribution ... dominates the production of ECs".

"Recent observations have removed from NASA's asteroid impact hazard list the near-Earth object (NEO) known to pose the most significant risk of Earth impact over the next 100 years."

"2007 VK184, an asteroid estimated to be roughly 130 meters in size, has been on NASA's Impact Risk Page maintained by the NEO Program Office at the Jet Propulsion Laboratory (JPL) for several years, with an estimated 1-in-1800 chance of impacting Earth in June 2048. This predicted risk translates to a rating of 1 on the 10-point Torino Impact Hazard Scale. In recent months, 2007 VK184 has been the only known NEO with a non-zero Torino Scale rating."

"2007 VK184 was discovered in November 2007 by the NASA-funded Catalina Sky Survey (CSS) at the University of Arizona and tracked by the CSS and other stations for two months before moving beyond view of ground based telescopes in January 2008."

"But in the early morning hours of March 26 and 27, 2014, Dr. David Tholen of the University of Hawaii sighted 2007 VK184 once again. Using the 3.6-meter-diameter Canada-France-Hawaii Telescope at the Mauna Kea Observatories in Hawaii, he was able to detect and track the asteroid. Because it had not been observed for almost six years, its predicted position was only approximate. Nonetheless, Dr. Tholen was able to find it within the predicted search region, which is called a "recovery." He measured the asteroid's position and movement relative to the background of stars, and forwarded his tracking data to the Minor Planet Center (MPC) in Cambridge, Massachusetts, the central node for the global NEO observer community."

"Although the asteroid will be closer to Earth and brighter in May, I made the recovery attempt in March because I didn't want the position uncertainty to grow so much that it would force a time-consuming search of much more of the sky. The trade-off was increased exposure time to detect such a faint, distant object. Greater atmospheric turbulence on March 26 blurred the images of the asteroid enough to make the detection questionable, but the March 27 images were much better and confirmed the recovery."

"The "Sentry" asteroid monitoring system at JPL automatically retrieved the new observations of 2007 VK184 from the MPC database, updated the orbit for the object, and computed a new impact hazard assessment. This new work shows that 2007 VK184 will pass no closer than 1.9 million kilometers (1.2 million miles) from the Earth in June 2048, with no closer encounters predicted for the foreseeable future. The NEO Program Office removed 2007 VK184 from the Impact Risk Page about three hours after receiving Dr. Tholen's observations from the MPC."

"While these new observations of 2007 VK184 were challenging for Dave Tholen to obtain, they were reported quickly, and the global, distributed NEO impact hazard monitoring system worked smoothly to provide the all-clear for this object."

"JPL's Sentry is an automated monitoring system that continually scans the most current catalog of known asteroids and predicts potential hazards of impacts with Earth over the next 100 years. As additional observations become available, objects will be removed from Sentry's Impact Risk Page when sufficient data become available to eliminate any potential for impact in the projected future. According to the Torino Impact Hazard Scale, developed and used by NEO observers to assess potential impact risks, a rating of 1 indicates a predicted event that "merits careful monitoring," and a rating of zero indicates the predicted event has "no likely consequences.""

"Objects typically appear on the Sentry Impact Risk Page because a limited number of available observations may indicate a potential hazard of impact with Earth but do not provide astronomers enough information to precisely define their orbital movements. Whenever a newly discovered NEO is posted on the Sentry Impact Risk Page, the most likely outcome is that the object will eventually be removed as new observations become available, the object's orbit is more precisely known, and its future motion is more tightly constrained. NASA's NEO Program Office at JPL, which operates Sentry, receives asteroid observations and orbit predictions daily from the MPC. Once an asteroid is classified as a near-Earth object, the Sentry system automatically calculates orbit updates for it as new data become available."

"NASA's Near-Earth Object Observation (NEOO) Program, located in the Planetary Science Division of the Science Mission Directorate at NASA Headquarters in Washington, D.C., is responsible for finding, tracking, and characterizing near-Earth objects (NEOs) - asteroids and comets whose orbits periodically bring them close to Earth. The NEOO Program sponsors internal NASA and external research projects. The Jet Propulsion Laboratory (JPL) in Pasadena, California, manages a NEO Program Office for the Headquarters' NEOO Program and conducts a number of NASA-sponsored NEO projects."

"Asteroid 2007 VK184 is another case study on how our system works."

"We find them, track them, learn as much as we can about those found to be of special interest - an impact hazard or a space mission destination - and we predict and monitor their movement in the inner solar system until we know they are of no more concern."

The image at right is of asteroid 2012 LZ1 using the Arecibo Planetary Radar.

"On Sunday, June 10, a potentially hazardous asteroid thought to have been 500 meters (0.31 miles) wide was discovered by Siding Spring Observatory in New South Wales, Australia. Fortunately for us, asteroid 2012 LZ1 drifted safely by, coming within 14 lunar distances from Earth on Thursday, June 14."

"Asteroid 2012 LZ1 is actually bigger than thought… in fact, it is quite a lot bigger. 2012 LZ1 is one kilometer wide (0.62 miles), double the initial estimate."

Asteroid "2012 LZ1′s surface is really dark, reflecting only 2-4 percent of the light that hits it — this contributed to the underestimated initial optical observations. Looking for an asteroid the shade of charcoal isn’t easy."

“This object turned out to be quite a bit bigger than we expected, which shows how important radar observations can be, because we’re still learning a lot about the population of asteroids”.

“The sensitivity of our radar has permitted us to measure this asteroid’s properties and determine that it will not impact the Earth at least in the next 750 years”.

Recent history
The recent history period dates from around 1,000 b2k to present.

Def. a "crevasse that separates flowing ice from stagnant ice at the head of a glacier" is called bergschrund.

The image at the right from 1936 shows explorers on Skillet Glacier. "Bergschrund is visible as the dark band of ice in the background."

Sedimentology encompasses the study of modern sediments such as sand, mud (silt), and clay, and the processes that result in their deposition.

Sedimentary rocks cover most of the Earth's surface, record much of the Earth's history, and harbor the fossil record. Sedimentology is closely linked to stratigraphy, the study of the physical and temporal relationships between rock layers or strata.

Triassic
The Triassic/Jurassic boundary occurs at 205.7 ± 4.0 Ma (million years ago).

The Permian/Triassic boundary occurs at 248.2 ± 4.8 Ma (million years ago).

Structural geology
The image at the right shows rock strata in Cafayate, Argentina, the subject of stratigraphy.

Structural geology is the study of the three-dimensional distribution of rock units with respect to their deformational histories.

Technology
Here at the right an under water, under-ice bubble trap is installed in a lake in Siberia.

Aircraft
The "Stratospheric Observatory for Infrared Astronomy [(SOFIA) is] mounted onboard a Boeing 747SP. [...] SOFIA’s 2.7 m mirror and optimized telescope system combines the highest available spatial resolution with excellent sensitivity. SOFIA will operate in both celestial hemispheres for the next two decades."

It has an operating altitude of 12-14 km, 39,000-45,000 ft and a spatial resolution of 1-3" for 0.3 < λ < 15 µm, and λ/10" for λ > 15 µm.

Hypotheses

 * 1) Earth is a rocky object throughout most of its interior and exterior.