Download THE EARTH`S SPHERES INTRODUCTION

THE EARTH’S FOUR SPHERES
Environmental science studies the interactions between the physical, chemical, and biological
components of the environment, including their effects on all types of organisms. Earth science
(also known as geoscience), is an inclusive term for all sciences related to Earth (geology,
meteorology, oceanography, etc). Although environmental and earth science cover essentially
the same material, environmental science places greater emphasis on the biological realm, while
earth science places greater emphasis on the physical realm.
Environmental and earth science study the interactions of five major systems or “spheres”
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The geosphere consists of the core, mantle and crust of the Earth.
The atmosphere contains all of the Earth’s air and is divided into troposphere,
stratosphere, mesosphere, thermosphere and ionosphere.
The hydrosphere contains all of the solid, liquid and gaseous water on Earth, extending
from the depths of the sea to the upper reaches of the troposphere where water is found.
Ninety-seven percent of the hydrosphere is found in salty oceans, and the remainder is
found as vapor or droplets in the atmosphere and as liquid in ground water, lakes, rivers,
glaciers and snowfields.
The biosphere is the collection of all Earth’s life forms, distributed in major life zones
known as biomes: tundra, boreal forest, temperate deciduous forest, temperate grassland,
desert, savannah, tropical rainforest, chaparral, freshwater, and marine.
The exosphere is space. It begins at the highest levels of the atmosphere and goes on to
infinity. Our solar system, the Milky Way Galaxy and all the other galaxies and
everything in-between is included in the exosphere.
Although the four systems have their unique identities, there is substantial interaction between
them. Environmental scientists study the effects of events in one sphere on the other spheres.
For example, a volcanic eruption in the geosphere may cause profound direct and indirect effects
on the hydrosphere, atmosphere and biosphere as follows:
Example 1 (Volcano) On May 18, 1980, Mount Saint Helens, in the state of Washington,
erupted. This event altered the surrounding environment, and provided scientists with an
opportunity to study the effects of volcanic eruptions on the geosphere, hydrosphere, atmosphere
and biosphere. Such studies are vital because volcanic eruptions will continue to occur, and will
have increasing impact on humans as people continue to settle lands closer to dormant
volcanoes. The following are but a few of the myriad of interactions resulting from a volcanic
eruption.
Volcano >> geosphere >> atmosphere >> hydrosphere >> biosphere
Volcanoes (an event in the geosphere) release a large amount of particulate matter into the
atmosphere. These particles serve as nuclei for the formation of water droplets (hydrosphere).
Rainfall (hydrosphere) often increases following an eruption, stimulating plant growth
(biosphere). Particulate matter in the air (atmosphere) falls out, initially smothering plants
(biosphere), but ultimately enriching the soil (geosphere) and thereby stimulating plant growth
(biosphere).
Volcano >> geosphere >> hydrosphere >> biosphere
Volcanoes (events in the geosphere) may release a substantial amount of hot lava (geosphere),
which causes mountain glaciers (hydrosphere) to melt. Mudflows (geosphere) and flooding may
occur downstream from volcanoes and may inundate streamside communities (biosphere).
Volcano >> geosphere >> atmosphere >> biosphere >> geosphere
Volcanoes (events of the geosphere) release a large amount of carbon dioxide (atmosphere), the
raw material for sugar production in plants (biosphere). This may increase photosynthetic
production and eventually increase the amount of biomass, which, after a very long time, forms
coal and oil deposits (geosphere).
Volcano >> complex interactions
Volcanoes (geosphere) may emit large quantities of sulfur dioxide (atmosphere). When
atmospheric sulfur dioxide combines with water (hydrosphere), sulfuric and sulfurous acid form.
Rain (hydrosphere) may bring these acids to the Earth, acidifying soils (geosphere), lakes and
rivers (hydrosphere). Acidic water leaches nutrients from the soil (geosphere) into the water
table (hydrosphere), making the soil less fertile for plants (biosphere), and the subterranean water
supply (hydrosphere) less potable for humans (biosphere). Acid rain falling on lakes and streams
reduces the pH of the water (hydrosphere), which may result in a decrease in phytoplankton and
zooplankton growth (biosphere). If photosynthesis is reduced, atmospheric concentrations of
carbon dioxide can build up and stimulate global warming (atmosphere) which may contribute to
increased melting of glaciers (hydrosphere).
Exosphere
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:
1. The angle of tilt of the Earth's axis varies from 22 to 24 degrees over a period of
about 41,000 years.
2. Precession - Earth's axis wobbles or moves in a circle like a spinning top, over a
period of about 26,000 years.
3. Orbital eccentricity - Earth's orbit around the Sun changes from more circular to
more elliptical by about 2% over a period of about 100,000 years. Glaciations would
presumably occur when the orbit is most elliptical and Earth is farthest from the Sun.
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 onethird 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.