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
Volcanoes eject material from below the Earth’s surface to the top of the Earth’s surface. Dust also travels with wind and can end up halfway around the world. Additionally, CO2 from the atmosphere is fixed by plants and those are eaten by animals. They all die and end up as part of the Earth. CO2 to fuel this can come from volcanoes, the oceans, or released by erosion.
A lot of stuff comes to earth from space for millions of years, which adds up to the Earth’s mass.
>Every day, Earth is bombarded with more than 100 tons of dust and sand-sized particles.
>About once a year, an automobile-sized asteroid hits Earth’s atmosphere, creates an impressive fireball, and burns up before reaching the surface.
>Every 2,000 years or so, a meteoroid the size of a football field hits Earth and causes significant damage to the area.
From nasa(dot)gov.
There’s a lot of stuff and it keeps getting recycled.
The continental plates are being pushed together in some places and one might get pushed underneath another one. The one that gets pushed underneath gets melted back into the mantle (basically lava). In other places the plates are being pushed apart or sliding against each other and new rocks are created where lava solidifies.
So rocks become lava and lava becomes rocks.
Rocks get pushed up high into mountains and water and wind erodes them away and they get carried with wind and water down to the sea where they create layers of sediment. Those layers either get lifted up over time or get further buried and melt back into lava.
And all of this keeps happening all of the time over and over and over again.
There is just a lot of it so sometimes the same bits of rock get metamorphosed and eroded sedimented and eroded and metamorphosed over and over and over again while other rocks might get more completely destroyed and melted back into the earth’s mantle.
The earth is very big even compared with the biggest mountains – so the bits that get built into mountains or eroded away into sediment don’t really mean a lot compared with the huge volume of crust there is on earth (it’s thinner under the ocean, but it covers the whole earth).
So while we have lost a LOT of geological history that can never be recovered because it’s all been melted (basically)… there is SO much crust and it doesn’t all get recycled at anything like an even rate so there are plenty of really really old layers of rocks as well as much “newer” rocks being built all the time from undersea volcanoes.
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.
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