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
From erosion, which is why river valleys and deltas have traditionally some of the best farming. Also from bio matter breaking down from plants and animals.
The new dirt on top of one location came from dirt eroding away from another. The history in the one place gets buried, and the history of the other place gets erased. Whether a location gets buried or eroded can change with time, so some location might not have any dirt from the period of 5000YA-7000YA for example, but when digging the dirt from 7001YA will still be below the dirt from 4999YA.
Decaying plant material, volcanic dust, erosion from mountains and rocks all create new layers and deposits burying ancient cities. https://youtu.be/EofirRBIh28
On land, you can easily see dirt forming around you. It’s the natural remnants of a crumbling world: trees decay, drop leaves, animals poop, living things die, rocks erode and turn to dust …all this matter becomes dirt. Now imagine a new volcanic rocky outcrop emerging from the ocean. It’s barren. But over time, life happens: seabirds poop on it. Lichen spores blow in on the breeze, settle down, begin growing on the rock, and eating into it. They emit acid which helps break down the rock a litttle, but also hold onto dust in the air, and trap it, accumulating it. Rainfall and wind helps grind down the rock. In just a few years, a barren rocky island in the middle of the ocean begins to form dirt on top, and soon offers a home to seaborne seeds which happenstance washes ashore, to become the pioneers of a future forest.
One of the ways, which I studied and went to school for, is dust.
Aeolian processes, also spelled eolian,[1] pertain to wind activity in the study of geology and weather and specifically to the wind’s ability to shape the surface of the Earth (or other planets). Winds may erode, transport, and deposit materials and are effective agents in regions with sparse vegetation, a lack of soil moisture and a large supply of unconsolidated sediments. Although water is a much more powerful eroding force than wind, aeolian processes are important in arid environments such as deserts.[2]
https://en.m.wikipedia.org/wiki/Aeolian_processes
Rain can actually capture fine particles and deposit into soil. And of course, rivers and body’s of water collect and deposit sediment. Ocean waves break down rock and deposit sand and mud and lime, which become sandstone, shale and limestone.
The science is called geomorphology, i.e. the scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or near Earth’s surface.
https://en.m.wikipedia.org/wiki/Geomorphology
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.
It’s simple really.
I’ll try to explain it to a five year old.
Have you ever left and forgotten a toy in the yard where grass grows? The grass gets tall and someone mows the lawn, maybe a couple of times before you go play in the same place.
You find that toy in the same spot where you left it, but now it is under the grass clippings instead of right on top, where you saw it last. Imagine this happening for years. The grass clippings get eaten by bugs and worms, and now that’s all dirt. No one moved the toy, but now it’s underneath.
This all happens even if no one is cutting the grass, because the plants will still shed leaves and eventually die and fall over becoming more dirt.
Earth is constituted of a diversity of sediment types, including sand, silt, and clay. A continuous process throughout billions of years, weathering and erosion from the effects of wind, water, and ice cause rocks and minerals to fragment into smaller bits. These fragments are transported by natural agents – rivers, glaciers, and wind – and accrete in sundry locations over years. Over millions of centuries, this process of settling, firming, and amalgamating culminates in sedimentary rocks – a significant component of the planet’s shell. Digging deeper you’ll reveal sediment and rock layers that provide insight into geological background.
Earth made of rock. Wind, rain, heat, etc. erodes rock. Sand is little rock bits. Sand mixes with minerals (which are just little pieces of different kinds of rock bits) and become dirt.
When I took an archaeology 101 class in college, this question always kind of bothered me. Sure, it makes sense that deeper things are older, but where does all the new dirt come from? I’d think that the earth was a closed system and all the dirt has been here for eons and there’s no new dirt. But reading these explanations it kinda makes sense
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