| Palaeos: | |
The Earth |
| ABIOTIC EVOLUTION | Earth Home |
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"Earth" is here used to refer mostly to the abiotic aspects of the planet, both in themselves and in relation to life, both abiotic and biotic components forming a holistic unity. The bulk of the planet is the geosphere, which consists of a thin crust , a relatively solid mantle, a liquid outer core (whose rotation generates the planet's magnetic field), and a solid iron inner core. In contrast to other worlds such as the moon and Mars, Earth's interior remains geologically active.
The crust is divided into a number of rigid tectonic plates, that over many tens and hundreds of millions of years, collide and then separate, forming cycles of supercontinents (such as Pangea) and smaller continents.
The name "Earth" is actually misleading, because more than two thirds of the surface of the planet is covered by water. The climate fluctuates through cycles of greenhouse (such as during the Mesozoic and early Cenozoic) and icehouse (Ice ages, such as the late Proterozoic, the Permo-Carboniferous and the Pleistocene). We are currently in the midst of an ice age, but Man's burning of fossil fuels has created an artificial greenhouse.
Earth is not the only world to be predominately water. Several outer planetary moons, such as Europa, have huge ice sheets, and possibly also liquid water underneath, raising the possibility of life on these worlds
Earth's atmosphere was originally of an abiotic, reducing kind, such as is still found on Saturn's moon of Titan today. But the evolution of life and the biosphere has significantly altered the Earth's atmosphere and other abiotic conditions on the planet, creating an oxygen environment that allows evolution of more complex (eukaryote) life, as well as an ozone layer which, together with Earth's magnetic field, screens out harmful solar radiation. It is only when there was sufficient oxygen that multicellular life could evolve, and only when the ozone layer reached a certain thickness that life on land became possible.
And, apart from a few pages, is all that we have on this topic for now, with only Paleogeography getting decent coverage. Hopefully in the future the other pages and topics will be filled out. MAK110913
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content by M. Alan Kazlev
checked ATW060124, last modified MAK110418. Edited RFVS111108
