Why so few?

[Jim78154]

Why are there so many impact craters on the moon and on planets other than Earth? I have heard it said that it is because of the atmosphere and the very high water content that we have here on Earth, and that erosion wipes away the traces of all but the largest impacts. But that doesn't explain it. Mars has an atmosphere. It isn't very dense, but it is still enough to whip up dust storms. True, Mars has very little water compared to Earth, but it still has an exponentially higher number of  impact sites than Earth. Furthermore it does not explain why meteorites are so rarely found on Earth. Shouldn't we be finding more of them?

[pipnina]

I think our atmosphere is somewhat thicker than mars' and, as such, blocks bigger meteors. The larger the meteor, the rarer the encounter. Earth's also got the far side of the moon as a shield  a very tiny one haha.

Craters on the moon are permanent (on the human time scale at least) on mars they may erode over hundreds of thousands of years or even millions... But mar's atmosphere is rather significantly thinner and dust storms aren't quite as erosive as running water and constant geological activity (earthquakes, volcanos, landslides, sinkholes,tsunamis etc).

TL;DR: Earth's atmosphere makes bigger asteroids burn up and earth's surface changes so rapidly (compared to mars or the moon) that only the biggest craters remain, but those, too vanish with time.

 

    ~pip

[Paz]

I guess plate tectonics also makes a difference.

[ShrewView]

It probably is mostly down to Earth being much more geologically active than the other inner planets and moon. Most of our planet's surface (around 70%) is covered with oceans and most of the crust underneath these gets recycled through subduction zones at plate boundaries. So there is almost none of it which is much older than 200 million years. Most of the meteorite bombardment happened billions of years before that so all those craters have gone. Those on continental landmasses get eroded away by rain, ice, wind etc.

[laudropb]

Plate tectonics mean that much of the Earths surface has been remodelled.

[symesie04]

Yes mainly due to atmosphere, weather and volcanism. However placement in the solar system im sure also plays a part. Mars the unlucky fellow is close to the asteroid belt and has Jupiter sitting the other side of it. Im sure if we could get clear views of Venus we would see a world similarly void of impact relics. All down to atmosphere, volcanism and proximity.

 

Oh and thinking about it i suspect mass also plays a part. Earth the most massive of the inner planets crush more impactors before they enter our atmosphere leaving only the larger ones to make to the surface.

[michaelmorris]

The majority of large craters and impact basins seen in the inner solar system will have occurred during a period known as the 'Late Heavy Bombardment' (around 4 billion years ago).  With the Earth having a geologically active surface (water erosion, wind erosion, sedimentation, volcanism, uplift, and plate tectonics) pretty much all signs of these impacts will have been erased long ago.

Meteorites are rarely found because only about 40,000 - 80,000 tonnes of meteorite reaches the surface every year. Whilst this may sound a lot, much of this will be fine dust.  Add to this the fact that most of the Earth's surface is covered with water and the fact that almost all the land is either covered with vegetation and or is uninhabited, and it's actually surprising how many meteorites are found!

[sheeprug]

27 minutes ago, michaelmorris said:

Meteorites are rarely found because only about 40,000 - 80,000 tonnes of meteorite reaches the surface every year. Whilst this may sound a lot, much of this will be fine dust.  Add to this the fact that most of the Earth's surface is covered with water and the fact that almost all the land is either covered with vegetation and or is uninhabited, and it's actually surprising how many meteorites are found!

 It does indeed sound like a lot,  and though I've no reasons to believe or disbelieve it, I do find myself wondering how they measure it.  I assume some extrapolation based on small area samples, but does anybody know?

SR

[symesie04]

46 minutes ago, sheeprug said:

 It does indeed sound like a lot,  and though I've no reasons to believe or disbelieve it, I do find myself wondering how they measure it.  I assume some extrapolation based on small area samples, but does anybody know?

SR

Easy once a year they just weigh the Earth 

[Paul M]

There is very little of Earth's crust that hasn't been recycled at least once since the period of heavy bombardment that battered the whole inner solar system in its youth.

Mars and the Moon have been relatively inactive geologically for billions of years and Mars' atmosphere hasn't supported liquid water for a similar time.

Here on Earth, weathering is a powerful force. When liquid water penetrates rock and then freezes it expands and blows the rock apart. That doesn't just happen on geological timescales. Here in the UK the bricks of modern houses start to show such weathering after just decades. The faces of the bricks simply fall off leaving a more porous surface for the action to continue apace.

Flowing water is also a powerful even violent force. It erodes rock and deposits sediments. Great for flattening high things and filling low things!

The very few craters visible on Earth, such as Barringer Meteor Crater in Arizona are either or both very young / located in arid environments.

 

[Stub Mandrel]

Think how well disguised the Chixulub Crater is (the 110 mile across Dino Killer) and that's only had 65M years to wear away, let alone the 4,000M that most have had. Plus there are very few areas of pre-cambrian & hadean roack left at the surface.

[DaveS]

Here's a list from Wiki

https://en.wikipedia.org/wiki/List_of_impact_craters_on_Earth

A good few pre-cambrian, but nothing from the Hadean.

And another possibly older one in Greenland, where the some of the oldest rocks are to be found.

https://www.newscientist.com/article/dn21996-earths-oldest-impact-crater-found-in-greenland/