Sunday, January 24, 2021

Earth is alive

The Earth we inhabit is far different than the world of the past. Although the Earth appears relatively stable and unchanging, it is in fact constantly in motion and changing. Even the ground beneath our feat is unstable. The surface on which most forms of life inhabit, where we humans have built our towns and cities, is a layer of crust a mere 30 km deep (on average). In fact, if the Earth were an apple, the crust would be about as thick as the apple’s skin, comprising a mere 0.5% of the total thickness of our blue marble. Given how little of our planet is actually the crust in which we inhabit, it’s truly mind boggling to know that every event in human history, from when we left the trees until now, has occurred on this paper-thin layer of rock. Beneath our crust is a layer of semi-molten rock called the upper mantle or lithosphere (the lithosphere comprises the lower section of the crust as well). Here, temperatures and pressures are sufficient enough to partially melt rock. The partially melted rock actually flows, albeit very slowly. Like an extremely viscous paste, the rock slowly moves underneath the crust. The lithosphere is also relatively thin, being around 100 km thick. Beneath the lithosphere is another section of the mantle called the asthenosphere. It’s this region of Earth’s interior that is responsible for the gradual movement of Earth’s plates. In the asthenosphere, rock is still only partially melted, although the much higher temperatures allow it to flow much faster than it does in the lithosphere. The flowing rock in the asthenosphere carries the crust above it from one location to another, gradually reshaping the surface above. The continents we recognize today didn’t always have the appearance they do, and many millions of years from now, the continents and land masses we’re familiar with will have moved and become unrecognizable.

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