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The Earths interior (University of Chicago)
The layers beneath our feet, starting from where we stand down to the geometrical center of the planet, are namely the crust, the mantle, the outer core, and the inner core. Those above us, on the other hand, starting from the one immediately surrounding us, are the troposphere, the stratosphere, the mesosphere, the thermosphere, and the exosphere.
Those layers above us are actually layers of the atmosphere, the sea of air that wraps itself around the Earth and protects it from cosmic radiation and meteoroids.
Notice how the layers of the atmosphere (including the ‘atmosphere’ itself) include the word ‘sphere’. That’s because those layers, including those layers underneath us are actually concentric spheres that encapsulate the ones beneath (or rather, inside) them.
To give us an idea of the dimensions of the layers of the Earth, we note that the Earth’s mean radius is about 6,371 km. By comparison, the exosphere’s upper boundary extends up to about 190,000 km from the Earth’s surface.
This upper boundary of the exosphere is defined as the boundary beyond which the influence of solar radiation pressure on atomic hydrogen is already larger than that of the Earth’s gravity. However, if we simply define the upper boundary based on where the geocorona (the luminous part of the Earth’s atmosphere) is observable, then the exosphere should only extend up to about 100,000 km.
If you’ve seen Al Gore’s global warming documentary, “An Inconvenient Truth”, you should very well remember how he described the atmosphere as a very thin layer. If we use any of the upper boundaries of the exosphere here, then the atmosphere is certainly not thin. However, I think Gore was simply referring to the thickness of the atmosphere up to the stratosphere, which is only about 50 km from the Earth’s surface.
It is in the stratosphere where heating due to the absorption of ultraviolet radiation occurs.
Although a lot is known (with a high degree of certainty) about the layers above us, most of what we know about the layers of the Earth underneath us are simply based on samples brought to the surface by volcanic activity, seismic waves, gravitational field measurements, and simulations using values of temperature and pressure believed to be present in the Earth’s interior.
Want to learn more about the atmosphere and air pressure? You can read about both here in Universe Today.
Of course, you can find more info at NASA too. Follow these links:
Earth’s Atmosphere
Earth
Tired eyes? We recommend you let your ears do the work for a change. Here are some episodes from Astronomy Cast:
Atmospheres
Plate Tectonics
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