The Earth’s System<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

2010-02-21

  Park Jae-Won

    Over 2000 years ago, humans thought ‘What is our world created of?’ The answer was the atmosphere, hydrosphere, and the lithosphere. Well soon in the 20th century human added one more thing; organisms. Scientist found out that not only the atmosphere, hydrosphere, and the lithosphere is the thing that is making up the Earth, also we ‘organisms’ are making up the Earth.

1. Atmosphere

First, let’s take a look at the atmosphere. The atmosphere is what organism breath in the combine with glucose, and to make energy to survive. But not only that, the atmosphere also protects the earth. When a space object runs into the earth at a very high velocity the air molecules will collide with the object. The kinetic energy will be alternated into heat and light energy. The temperature will be about 3000 degrees. And before it reaches earth, the object will broke into pieces, and the earth is safe!

    The atmosphere is divided into 4 groups. The troposphere, stratosphere, mesosphere, and the thermosphere. The troposphere is the atmosphere where we live. When we go higher, the Earth radiation’s amount will be lowered. So when we go higher, the temperature will go lower.  

    The stratosphere is route for airplanes. There is the ozone layer that absorbs the ultraviolet radiation, As we go higher the temperature will go higher! First we must know how ozone is created.  It is a layer of ozone (the molecule that is bonded with 3 oxygen atoms) in stratosphere about 25km above. When the oxygen atoms get ultraviolet radiation O2 splits into O+O. When O meets with O2 in the atmosphere they bond together to make O3. But before ‘02+0’ reaction they need a catalyst called N2. When N2 meets with 02+0, it helps the reaction go on faster making N2+03. After that when the 03 in the ozone layer absorbs the ultraviolet radiation it spilts into 02+0 again, also releasing heat. This process goes on and on as a clycle. Since it releases heat the temperature will go higher as we rise.

2. The lithosphere

In the Earth, the lithosphere includes the crust and the uppermost mantle, which constitute the hard and rigid outer layer of the Earth. The lithosphere is underlain by the asthenosphere, the weaker, hotter, and deeper part of the upper mantle. The boundary between the lithosphere and the underlying asthenosphere is defined by a difference in response to stress: the lithosphere remains rigid for very long periods of geologic time in which it deforms elastically and through brittle failure, while the asthenosphere deforms viscously and accommodates strain through plastic deformation. The lithosphere is broken into tectonic plates.

The concept of the lithosphere as Earth’s strong outer layer was developed by Barrell, who wrote a series of papers introducing the concept.^[2][3][4] The concept was based on the presence of significant gravity anomalies over continental crust, from which he inferred that there must exist a strong upper layer (which he called the lithosphere) above a weaker layer which could flow (which he called the asthenosphere). These ideas were expanded by Daly (1940)^[5], and have been broadly accepted by geologists and geophysicists. Although these ideas about lithosphere and asthenosphere were developed long before plate tectonic theory was articulated in the 1960s, the concepts that strong lithosphere exists and that this rests on weak asthenosphere are essential to that theory.

The lithosphere provides a conductive lid atop the convecting mantle; as such, it affects heat transport through the Earth.

There are two types of lithosphere:

• Oceanic lithosphere, which is associated with Oceanic crust and exists in the ocean basins
  
  
• Continental lithosphere, which is associated with Continental crust
  

The thickness of the lithosphere is considered to be the depth to the isotherm associated with the transition between brittle and viscous behavior^[6]. The temperature at which olivine begins to deform viscously (~1000°C) is often used to set this isotherm because olivine is generally the weakest mineral in the upper mantle. Oceanic lithosphere is typically about 50-100 km thick (but beneath the mid-ocean ridges is no thicker than the crust), while continental lithosphere has a range in thickness from about 40 km to perhaps 200 km; the upper ~30 to ~50 km of typical continental lithosphere is crust. The mantle part of the lithosphere consists largely of peridotite. The crust is distinguished from the upper mantle by the change in chemical composition that takes place at the Moho discontinuity.

[edit] Oceanic lithosphere

Oceanic lithosphere consists mainly of mafic crust and ultramafic mantle (peridotite) and is denser than continental lithosphere, for which the mantle is associated with crust made of felsic rocks. Oceanic lithosphere thickens as it ages and moves away from the mid-ocean ridge. This thickening occurs by conductive cooling, which converts hot asthenosphere into lithospheric mantle, and causes the oceanic lithosphere to become increasingly thick and dense with age. The thickness of the mantle part of the oceanic lithosphere can be approximated as a thermal boundary layer that thickens as the square root of time. Here, h is the thickness of the oceanic mantle lithosphere, κ is the thermal conductivity (approximately 10^-6 m²/s), and t is time.

Oceanic lithosphere is less dense than asthenosphere for a few tens of millions of years, but after this becomes increasingly denser than asthenosphere. This is because the chemically-differentiated oceanic crust is lighter than asthenosphere, but due to thermal contraction, the mantle lithosphere is more dense than the asthenosphere. The gravitational instability of mature oceanic lithosphere has the effect that at subduction zones, oceanic lithosphere invariably sinks underneath the overriding lithosphere, which can be oceanic or continental. New oceanic lithosphere is constantly being produced at mid-ocean ridges and is recycled back to the mantle at subduction zones. As a result, oceanic lithosphere is much younger than continental lithosphere: the oldest oceanic lithosphere is about 170 million years old, while parts of the continental lithosphere are billions of years old. The oldest parts of continental lithosphere underlie cratons, and the mantle lithosphere there is thicker and less dense than typical; the relatively low density of such mantle "roots of cratons" helps to stabilize these regions