Saturday, January 11, 2014

How much has life reshaped Earth?

Earth has hosted life for much of its geological existence, and living things have changed much of Earth's geological properties-- from local patterns of erosion to the composition of the atmosphere, living things put their visible stamp on Earth. A recent interview with Tilman Spohn in Astrobiology  magazine asks whether life has transformed Earth even more deeply, by affecting the process of continental drift.
The focus of the question is the extent to which biological weathering at the surface can change the contents of the underlying mantle on which the continents float. Living things such as lichen or bacteria accelerate the breakage of rocks, generating sediments, which are eventually washed to sea. At sea these sediments can accumulate in subduction zones, places where the earth's surface dips down toward the lower layers.
What makes this important is the enormous water content of weathered rock sediments. Water carried down into the mantle would soften the mantle, increasing the overall churn. In computer simulations, an increase churn of mantle rocks leads to increased continental movement and breakage.

So, if life has sufficiently changed (or is still changing) which rocks get weathered, and how fast, these changes would alter the entire face of the planet-- encouraging more tectonic plates and motions.  

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