How does the earths first gain more layers if there is a finite amount of material?

Question

When we learn about history we learn that layers at the bottom are older and stuff up top is newer, so it’s like things just keep piling up. Where did we get the stuff then? Will we run out of stuff?

In: Geology

Answer 1

We live on a very active planet, and it’s spent the best part of 4,500,000,000 years in a constant state of recycling material. The denser materials have tended to find their way down into the core, while the lighter materials have found their way toward the surface. The very lightest form our atmosphere, and the continentnal crust we live on can be thought of as a kind of ‘scum’ floating on the surface that is not dense enough to get recycled back into the mantle.

That said, that ‘scum’ gets a lot of forces applied to it. Contientnal plates get squeezed, and squashed, and pulled apart, and pushed back together again over millions of years. That process results in mountains being formed, and together with the atmosphere that means there’s lots of surface processes that result in erosion and weathering.

Erosion breaks down the rocks that get exposed at the surface, and then transports those fragments down slope under the force of gravity. This is usually helped by rivers and streams, or winds, or glaciers.

And that erosion process moves material from high up to low down. That means that low-lying areas accumulate sediment, and high areas get eroded down. This is why we have excellent preservation of lake, flood plain and marine environments, while we have almost no preservation of mountainous environments.

While some depositional systems like volcanic ash deposits and loess (wind-blown dust) can blanket all topographies, these tend to get eroded again from the high areas before they are ever preserved.

The other component is biological build-up; in some environments the growth of vegetation and accumulation of biomatter will thicken soils up. This is particularly notable in places like peat bogs.

So most of it is simply recycling of material around the surface and from and to the atmosphere. Relatively little is new addition by volcanic action.