When looking at a geological timescale, typically ‘the deeper you dig, the older stuff gets’, right?
So, where does this buildup of new sediment come from?
I understand we’re talking about very large timeframes here, but I still dont really get it.
In: 19
The rock cycle, and the life cycle.
[Rock cycle](https://en.wikipedia.org/wiki/Rock_cycle): liquid rock in the form of magma or lava comes to the surface and cools, becoming solid rock. This happens because of [plate tectonics](https://en.wikipedia.org/wiki/Plate_tectonics) and convection currents in the mantle. This process results in [mountains made of this new rock](https://en.wikipedia.org/wiki/Orogeny). Then, these mountains weather and erode. Weathering is when big rock breaks into small rock. Could be because of chemical reactions, water and wind wearing it down, or a bunch of other processes. Erosion is when the small rocks are moved away from where the big rock used to be. Wind, water, and gravity are the big movers. Eventually, a mountain will disappear and somewhere else gets a whole bunch of sand, silt, and dust.
Example: The great Plains of North America used to be [underwater](https://en.wikipedia.org/wiki/Western_Interior_Seaway). A mountain range we call the Ancestral Rockies weathered and eroded away and filled in this ancient sea. Then, plates collided and lifted up the whole western side of the continent even higher, draining whatever was left, and then weathered and eroded again, leaving behind today’s Rocky Mountains and Great Plains.
Life Cycle: Things live, grow, die, and decay. Soil is made of both tiny bits of rock (sand, silt, and clay) AND tiny bits of dead things (plants, microorganisms, bugs, etc). Healthy soil will also still have a lot of living things in it, mostly microorganisms (bacteria, fungi, really tiny worms, etc).
Example: Plants. Plants grow by taking CO2 out of the air and turning it into very complex carbohydrates like starch, cellulose, or lignin through photosynthesis. They quite literally create themselves out of thin air. By making this gas into something solid, they can add to the amount of dirt when they die. A tree spends its life turning CO2 into wood, and then it dies and all that wood decays and becomes dirt.
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