Earth Systems
Earth Systems
This section addresses, in whole or in part, the following Georgia GPS standard(s):
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This section addresses, in whole or in part, the following Benchmarks for Scientific Literacy:
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This section addresses, in whole or in part, the following National Science Education Standards:
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The Earth can be viewed as a series of interrelated systems or spheres. Any changes which occur to one of these systems affect the others. These Earth systems are as follows:
In geology, we study natural processes affecting human health and safety (for example, earthquakes, floods, volcanic eruptions, and landslides). We learn how the Earth's human population depends on Earth resources.
Resources include soils for growing crops, freshwater for drinking, washing and irrigation, as well as energy resources (coal, oil and gas). Other resources include rocks and minerals used in manufactured goods and construction (for example, calcite for cement; hematite for iron ore used in steel-making; gold, silver, and diamonds used in jewelry; halite as table salt; kaolin used in rubber, paints, and plastics; copper used for wire; graphite used for pencil leads and lubricants; various types of rock used for building and paving stone).
We also learn the consequences of human activities on Earth processes (groundwater contamination and depletion, subsidence, coastal erosion caused by the damming of rivers, atmospheric and climatic changes leading to sea level rise as a result of burning energy resources). Humans are a part of the Earth system. We depend on the Earth, we impact it, and we are affected by its changes.
The geosphere is the solid Earth, including the continental crust, the oceanic crust, and the layers of the Earth's interior (crust, mantle, and core). The outer part of the Earth, consisting of the crust and uppermost mantle, is sometimes called the lithosphere. The lithosphere is the rigid, rocky layer that makes up the Earth's tectonic plates. Below the lithosphere is a part of the mantle that flows, called the asthenosphere. Convection and flow in the asthenosphere causes the tectonic plates to move.
The Earth's crust is primarily composed of the elements oxygen and silicon, along with lesser amounts of aluminum, iron, calcium, sodium, potassium, and magnesium. Oxygen and silicon are the two dominant elements in the ROCK-FORMING MINERALS (called silicate minerals) that make up the Earth's crust.
| Element | Abundance |
|---|---|
| Oxygen (O) | 46.6% |
| Silicon (Si) | 27.7% |
| Aluminum (Al) | 8.1% |
| Iron (Fe) | 5.0% |
| Calcium (Ca) | 3.6% |
| Sodium (Na) | 2.8% |
| Potassium (K) | 2.6% |
| Magnesium (Mg) | 2.1% |
The Earth, as a whole, has a slightly different chemistry overall, because of the concentration of iron at its center. So for the Earth as a whole, iron is the most abundant element, followed by oxygen, silicon, and magnesium.
| Element | Abundance |
|---|---|
| Iron (Fe) | 35% |
| Oxygen (O) | 30% |
| Silicon (Si) | 15% |
| Magnesum (Mg) | 13% |
| Nickel (Ni) | 2.4% |
| Sulfur (S) | 1.9% |
| Calcium (Ca) | 1.1% |
| Aluminum (Al) | 1.1% |
| Sodium (Na) | 0.57% |
| Other elements | Less than 1% |
The atmosphere is a critical part of the Earth system that interacts with the solid Earth and other systems. The atmosphere is the layered envelope of gases that extends from the surface of the Earth to an altitude of approximately 1,600 km (1,000 mi). Almost 99 percent of the atmosphere lies within 30 km (18 mi) of the surface.
The Earth's atmosphere is approximately 78% nitrogen, 21% oxygen, with traces of argon, carbon dioxide, water and other gases.
The presence of free oxygen is quite remarkable from a chemical point of view. Oxygen is a very reactive gas and under "normal" circumstances would quickly combine with other elements. The oxygen in Earth's atmosphere is produced and maintained by biological processes. Without life there would be no free oxygen.
There was probably a very much larger amount of carbon dioxide in the Earth's atmosphere when the Earth was first formed, but it has since been almost all incorporated into carbonate rocks and to a lesser extent dissolved into the oceans and consumed by living plants. Plate tectonics and biological processes now maintain a continual flow (or cycle) of carbon dioxide from the atmosphere to these oceans and plants, and back again.
The tiny amount of carbon dioxide in the atmosphere helps maintain the Earth's surface temperature via the "greenhouse effect". The "greenhouse effect" raises the average surface temperature about 35 degrees C above what it would otherwise be (from a frigid -21 C to a comfortable +14 C); without the "greenhouse effect", the oceans would freeze and life as we know it would be impossible.
Satellite image of the Earth showing the clouds in the atmosphere. Clouds are made of water vapor.
Image courtesy of
NASA.
The present composition of the lower atmosphere is:
|
Gas |
Symbol or Formula |
Percent by Volume |
|---|---|---|
|
Nitrogen |
N 2 |
78.08 |
|
Oxygen |
O 2 |
20.94 |
|
Argon |
Ar |
0.934 |
|
Carbon Dioxide |
CO 2 |
0.035 |
|
Neon |
Ne |
0.00182 |
|
Helium |
He |
0.00052 |
|
Methane |
CH 4 |
0.00015 |
|
Krypton |
Kr |
0.00011 |
|
Hydrogen |
H 2 |
0.00005 |
|
Nitrous oxide |
N 20 |
0.00005 |
|
Xenon |
Xe |
0.000009 |
The atmosphere is layered into four distinct zones of contrasting temperature:
The amount of scattering is much higher for shorter wavelengths of light (blue light) than for the longer wavelengths (red).
This is why the sky, which is lit by scattered light, is blue.
Note that when the sun or moon is on or near the horizon, they appear orange or reddish in color. The dust in the atmosphere scatters the long red wavelengths of light. (We are looking through more atmosphere when we are looking towards the horizon than when we are looking straight up, so we are looking through more dust particles.)
Volcanic eruptions release gases to the atmosphere. Some of these gases, such as sulfur dioxide, produce sulfuric acid droplets in the atmosphere called vog or volcanic fog, which adversely affects the biosphere including humans and plants.
Sulfur Banks, Hawaii Volcanoes National Park. Sulfur and other minerals are being deposited here from gases rising from the hot magma below.
The steam contains mostly water vapor, with lesser amounts of carbon dioxide and hydrogen sulfide.
For example, on Kilauea Volcano in Hawaii, upwind from the volcano is a tropical rain forest, and downwind from the volcano is the barren Ka'u Desert where the vog and acidic rain have killed the plants.
Ka'u Desert, Kilauea Volcano. Note the absence of plants, although rainfall is plentiful.
Many residents of Hawaii collect rainwater for drinking. When the acidic rain falls on roofs, it leaches lead from roofing nails and paint. As a result, the rainwater captured for drinking is contaminated with lead, creating a health hazard.
House on the island of Hawaii that catches rainwater for drinking, which becomes contaminated with lead from the acid rain.
Image courtesy of USGS.
(USGS photo by J. D. Griggs).
The hydrosphere is the liquid water on Planet Earth. Water moves from the oceans to the atmosphere through evaporation, falls as precipitation, and then runs across the land into the ocean, or percolates into the ground to become part of the groundwater. The hydrosphere includes the salt water in the oceans, as well as lesser amounts of fresh water in rivers and lakes, and underground.
The hydrosphere contributes to the chemical weathering of rocks and minerals, such as dissolution, which can lead to the formation of underground caves in limestone, and the formation of sinkholes, which can affect manmade structures.
Sinkhole at Winter Park, Florida that opened in one day in 1981.
Sinkholes form when carbonate layers beneath the ground surface dissolve.
When the weight of the overlying ground becomes too great, or the water table drops, leaving an unsupported void,
or if the dissolved area is too large, the surface collapses into the void, forming a sinkhole. Photograph by A. S. Navoy.
Image courtesy of USGS.
Water is the major agent of erosion of the Earth surface. When water flows over land it picks up and transports particles of sediment, and can also carry elements which have been dissolved from rocks and minerals. The sediment and chemical constituents are transported downstream by running water. Gulleys and canyons can form readily in areas underlain by soft sediment, as running water erodes it and carries particles away. Over long periods of time, canyons can even be worn into hard sedimentary rocks by the action of running water. For example, the Grand Canyon was cut by the erosive power of the Colorado River. Over long periods of geologic time, erosion by water can wear down mountain ranges. Eroded sedimentary particles are eventually deposited in sedimentary environments, such as deltas, beaches, submarine fans, or on the continental shelf.
Furthermore, the moisture evaporating from the oceans affects the weather patterns and weather events such as hurricanes.
Changes in the atmosphere and climate can also lead to the buildup of glacial ice sheets or the cryosphere, which covered vast areas of North America in the not-so-distant past (over the past 2 - 3 million years). Growth of the glacial ice sheets, several tens of thousands of years ago, lowered sea level about 450 feet below the present level, exposing the continental shelves. The water contained in the glacial ice came from the oceans which evaporated and fell as ice and snow - the hydrosphere. Climate and sea level changes forced the migration of plants and animals, including early humans, who migrated from Asia to North America across the Bering Strait. Later, the melting of these glacial ice sheets led to sea level rise, which caused the inundation or flooding of the continental shelves. If all of the ice in Antarctica today were to melt, sea level would rise another 240 feet, flooding many coastal cities including New Orleans, Miami, Savannah, Washington, DC, and New York.
Generalized geographic map of North America showing the extent of glacial ice coverage in the Pleistocene, which began about 2 million years ago.
ing the current edge of the continent. The continental shelves were exposed during the Ice Age. Image courtesy of USGS.
Atmospheric and climatic changes also affected water levels in lakes during the Ice Age. Increased rainfall in the area south of the North American glacial ice sheet formed large lakes in areas of Utah, Nevada, and California which are now desert. The Great Salt Lake, although one of the largest lakes in North America, covering 2500-6000 km2, is a much smaller, shallower (10 m or about 30 ft deep) remnant of ancient Lake Bonneville, which covered 50,000 km2 and was 300 m (about 1000 ft) deep about 15,000 years ago. Salt Lake City, built on the shores of the Great Salt Lake, would be under nearly 300 m (1000 ft) of water if the climate returned to what it was just 15,000 years ago during the Pleistocene.
The biosphere includes all life on Earth, past as well as present. All organisms are composed of cells--the fundamental unit of life. Most organisms are single cells; other organisms, including humans, are multicellular. Life is very diverse, including the plants, animals, fungi, protists, bacteria, and the archaea.
Life exists in diverse environments, including some very hostile environments such as those at the bottom of the sea (high pressures, always dark), in hot, acidic volcanic lakes, and deep beneath the surface of the Earth in fluids recovered from deep wells.
The remains and traces of past life are preserved as fossils. These are also part of the biosphere, and reflect complex and active communities of organisms (single-celled or multi-cellular) that lived in the past, as much as several billion years ago.
Fossils provide important evidence of how life and environmental conditions have changed through time on the Earth. We can examine fossils to learn about changes in sea level, and changing climates of the Earth through time.
The Earth is the only planet on which life is definitely known to exist.
The exosphere is the Earth in space. Beyond the limit of the Earth's atmosphere, beyond the thermosphere, is the exosphere.
The Earth is the third planet from the Sun in a system that includes the Moon, the Sun, eight other planets and their moons, and smaller objects, such as asteroids and comets.
The sun, an average star, is the central and largest body in the solar system. Most objects in the solar system are in regular and predictable motion. Those motions explain such phenomena as the day, the year, phases of the moon, and eclipses.
Gravity is the force that keeps planets in orbit around the sun and governs the rest of the motion in the solar system. Gravity alone holds us to the Earth's surface and explains the phenomena of the tides.
The sun is the major source of energy for phenomena on the Earth's surface, such as growth of plants, winds, ocean currents, and the water cycle. Our seasons result from variations in the amount of the Sun's energy hitting the surface, due to the tilt of the Earth's rotation on its axis and the length of the day.
How does the exosphere interact with the other Earth Systems?
Recent investigations have shown that glaciations seem to occur approximately every 100,000 years;
there may have been as many as 30 ice ages or glacial advances over the past 3 million years.
What could cause this cyclicity?
The cyclicity appears to be related to changes in the distance and angular relationships between the Earth and the Sun,
due to periodic fluctuations or oscillations in the Earth's orbit. Several cycles may be a factor, including the following:
This is one example of how the exosphere (Earth in space) influences the cryosphere (glaciers), the hydrosphere (sea level), the atmosphere (weather and climate), the geosphere (formation of windblown dunes in areas which are now humid and formation of deep lakes in areas which are now salt flats), and the biosphere (migration of plants and animals as sea level and climate change). All of these are interrelated.
Objects from space that collide with the Earth
The exosphere also affects the Earth when small (1 - 10 km in diameter) solar system objects, such as icy comets,
and rocky or metallic asteroids collide with the Earth and explode upon impact, creating large craters.
Solar system objects that cross Earth's orbit are referred to as Apollo objects.
Objects that collide with the Earth are referred to as bolides.
Bolide impacts are associated with times of biological extinction in Earth history.
An impact about 65 million years ago may have contributed to the extinction of the dinosaurs. A dust cloud ejected into the atmosphere by the force of the impact encircled the Earth leading to decreased solar radiation input (less sunlight reaching the surface of the Earth), decreased photosynthesis by plants, and the disruption of the global food chain, leading to worldwide extinctions.
Every few years, astronomers realize that Earth has had a near miss from a previously unknown asteroid. For example, in June 2002, a previously undetected asteroid the size of a football field missed colliding with Earth by a mere 75,000 miles (120,000 km), about one-third the distance to the moon, making it one of the closest encounters ever recorded.
The closest near collision in recent years occurred in 1994, when asteroid 1994XL1 passed within 65,000 miles (105,000 km) of Earth. In 1989, an asteroid the size of a battleship missed striking the Earth by a mere 6 hours (or about 800,000 km, or 500,000 mi). If it had struck the Earth, it would have created a crater 5 miles wide and nearly a mile deep, probably killing everything within 100 miles from the blast.
What if an asteroid like this struck a populated area?
Might an asteroid strike Earth in the future?
Astronomers are watching a newly discovered 2 km wide asteroid which could strike the earth on February 1, 2019,
but the odds are only 1 in 250,000 that a collision may occur.
Meteor Crater in Arizona is testimony to one of these impacts, which occurred relatively recently on a geologic time scale, only about 50,000 years ago.
Photograph of Meteor Crater about 38 miles east of Flagstaff, Arizona. Meteor Crater is a shallow, bowl-shaped impact crater, 1 km in diameter, with an upraised sub-circular rim. Image courtesy of USGS.
An impact about 35 million years ago during the Eocene, which occurred in the Chesapeake Bay region (Virginia-Maryland) ejected droplets of molten rock which flew through the air, cooling rapidly to form millimeter- to centimeter-sized glassy stones known as tektites. Tektites from this impact have been found in 17 counties in the coastal plain of east-central Georgia. The Georgia tektites are translucent and green, and are sometimes called "georgiaites".
Greenhouse Effect and Global Warming
As a further illustration of the interrelationship among the Earth systems, human activities can be shown to have an impact on the atmosphere. Certain gases in the atmosphere trap heat. This phenomenon is referred to as the greenhouse effect. Without the thermal insulation of the natural greenhouse effect, Earth would be covered by ice, and life as we know it would not exist. The fairly large input of carbon dioxide (CO2) from human activities can significantly affect the amount of heat trapped in the atmosphere. The following things can cause carbon dioxide levels to rise:
The total amount of CO2 in the atmosphere has increased by about 25% since the beginning of the industrial revolution. The accumulation of CO2 over the last 100 years has added as much heat to the Earth's climate system as would a 0.5% increase in the sun's energy output. Since the late 1800's, the mean global temperature has risen by about 0.3° - 0.6°C, and over the last 45 years, the temperature has increased by about 0.2 - 0.3°C. Recent years have been among the warmest on record. The increase in CO2 is projected to increase the Earth's natural greenhouse effect and lead to global warming. Possible consequences of global warming include:
Many uncertainties remain with respect to the exact consequences of global warming.
Disappearing glaciers are one indicator or consequence of global warming, whether due to manmade or natural changes. Glaciers are retreating on every continent (except Australia, which has no glaciers), and the rate of ice loss has more than doubled since 1988. Alpine or mountain glaciers are present on several continents, but most of them appear to be melting rapidly. For example, in the past 100 years, the number of glaciers in Glacier National Park, Montana, has declined from more than 150 to 37, and the Grinnell Glacier is retreating at more than 15 feet per year. At this rate, glaciers may disappear completely from Glacier National Park within 30 years. In Alaska, 99% of the named glaciers are retreating. Glacier Bay, Alaska was covered with ice when it was mapped in the 1700's, but since then, 95% of the ice has melted, over a distance of more than 60 miles; it is currently melting at about a half mile per year. In Europe, the glaciers in the Alps have shrunk by 50% since 1850. A glacier in the Andes Mountains of Peru (Quelccaya ice cap) is retreating at more than 500 feet per year. In Italy, Belvedere Glacier began to melt in fall 2001, forming a lake which is rising as much as 1 meter (3 ft.) per day, and is threatening to flood a nearby town. As the ice melts, things long entombed in the ice are exposed. For example, the mummified remains of a 5000 year old "ice man" clothed in animal skins with a copper ax were exposed in 1991 in melting ice in Italy near the border with Austria. In 1995, a frozen, mummified girl, at least 500 years old, was found in melting ice on Mount Ampato near Arequipa, Peru.
Why is the glacial ice melting? Spring temperatures are arriving earlier, autumn is continuing later, summers are warmer and longer, more precipitation is falling as rain rather than snow, and most years, more ice melts than is replaced by winter snowfall. As a consequence, snowmelt in northern Alaska now occurs about 40 days earlier than it did 40 years ago, plants are growing larger and spreading across previously barren territory, permafrost is melting, and the melting of sea ice is causing shoreline erosion. In other areas, flowers are blooming earlier than ever before, trees are leafing out earlier and leaves are falling weeks later, and birds are laying their eggs earlier. In Britain, spring flowers have begun to bloom before the trees have lost their leaves in the fall. There is a systematic pattern of ecological changes seen in nearly all major habitats ranging from the poles to the tropics. We do not know how much of the global warming is due to the actions of humans, and how much is the due to other natural causes. But we do see plenty of evidence for global warming.
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Page created by Pamela J.W. Gore
Georgia Perimeter College,
Clarkston, GA
Page created March 12, 2005
Updated May 16, 2008
Updated June 10, 2009
