Planet Earth Recycling

The Simon and Garfunkel song title "I am a Rock" is correct at a physical level since all material on the earth came originally from the earth's mantlehelp icon - with the exception of most water which is believed to have come from comet collisions with the Earth. Some material was also deposited from meteors, and this process is continuing on a smaller scale. Material is being recycled via the mantle on a very long time scale (i.e. 100's of millions of years) - below is my brief attempt at describing this process:

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Llyn Cwellyn, N Wales

Material is transferred from the earth’s mantle to the crusthelp icon at diverging boundaries of the the earth’s tectonic plateshelp icon (for example the Mid-Atlantic Ridge). Deposition of surface rock occurs where continental plateshelp icon converge (for example India and Asia). The energy for tectonic plate movement and heating of the mantle comes from the earth’s core.

Surface rocks are eroded by precipitation, heat, frost, wind and waves – mostly driven by energy from the sun, with some tidal erosion due to the gravitational force of the Moon. The eroded material may eventually become sedimentary rock such as sandstone, or combine with organic materialhelp icon to form soil.

Solar energy enables plant organisms of the biospherehelp icon to use soil, water and gases to grow and provide food for other lifeforms. Material is generally returned to land or ocean bed when organisms die [Note 1]. Skeletal remains may eventually form part of sedimentary rocks such as limestone.

Rock material is ultimately returned to the mantle in tectonic plate subduction zoneshelp icon (for example the Pacific coastline of the Americas), but loose soil and material is retained near the surface. Rock, ash, water and gases are emitted from volcanoes in these regions

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Note 1: An exception to this is people who pay to have their remains blasted into "space" (above 50 miles by one definition). The late "Scotty" from Star Trek and others who were rocketed into "space" recently disappointingly only achieved earth orbit. Eventually their ashes will probably return to earth - in the meantime will the ashes affect global warming? Is this an environmetally responsible procedure?

(This was written soon after the launch, however it was reported in August 2008 that the launch failed - thus some of Scotty's remains have already been scattered on earth rather expensively, in money and environmental damage terms. Undeterred, another attempt is to be made to propel more of Scotty's remains into space - the same questions apply!)

If you have an original explanation of "how the world works / recycles" send it in and I may include it on this page (200 words maximum please)