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Sand_Trout t1_iy4fdjl wrote

There are three major causes:

  1. Erosion. Wind, rain, snow, ect. gradually wear down craters on Earth's surface over time.

  2. Fewer surface impacts per m^2 . Because the Earth has a relatively thick atmosphere, a lot of the smaller rocks break up before hitting the surface or slow sufficiently to mitigate their impact on the surface.

  3. Tectonic activity. Unlike the Moon, the Earth is still tectonically active, with volcanos faults gradually erasing some craters.

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rslashmiko t1_iy4gee9 wrote

I'd add in a 4th. Coverage. There are a lot of craters that are covered by water, forests, etc.

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mr_oof t1_iy4l6oz wrote

Per #1: the Canadian Shield has some of oldest exposed rock on Earth, and has some huge craters- you just have to look really hard. Like, a large roundish lake with circle of small lakes on a satellite map, or a region of super-concentrated mineral deposits (both of which you see in the area around Sudbury, Ontario.)

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SlippySlappySamson t1_iy5vve4 wrote

  1. The moon. It has significant gravity and has historically attracted much of the debris headed our way, and thus has more craters to be visible.
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FowlOnTheHill t1_iy7ll0n wrote

Couldn’t the same be true about earth? It’s significant gravity pulls away debris headed to the moon?

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SlippySlappySamson t1_iy7o852 wrote

Yeah, of course! The nature of orbital mechanics (and I don't understand it well at all) and the frequency at which the Moon orbits the Earth means that it's likely that anything zooming in is probably going to encounter the Moon's gravity first, but it's by no means guaranteed.

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FowlOnTheHill t1_iy4heqt wrote

Atmosphere

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SpaceMonkee8O t1_iy660ev wrote

Yeah that’s the main difference.

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As_TheHoursPass t1_iy6zc2j wrote

It may not be. Chicxulub is absolutely massive but not visible from a normal satellite. It's been eroded by time. When you consider just how gargantuan that planet killer was, it gives erosion and plate tectonics a much stronger argument.

It wasn't even that long ago from a planetery age viewpoint, given its size.

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SpaceMonkee8O t1_iy6znti wrote

Granted our planet is much more geologically active and that definitively plays a part, but I feel like erosion is largely an atmospheric phenomenon.

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