# Asteroid hits moon, debris hits Earth ?

**URL:** <https://boards.straightdope.com/t/asteroid-hits-moon-debris-hits-earth/732439>\
**Category:** Factual Questions\
**Created:** [September 24, 2015, 11:00pm UTC](https://boards.straightdope.com/t/asteroid-hits-moon-debris-hits-earth/732439 "2015-09-24T23:00:40Z")\
**Posts on this page:** 3\
**Page:** 2

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**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\
**Post date:** [September 26, 2015, 2:37pm UTC](https://boards.straightdope.com/t/asteroid-hits-moon-debris-hits-earth/732439/21 "2015-09-26T14:37:16Z")

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> [@Whack-a-Mole](#):
>
> Can it be both?
> 
> Given the Earth is bigger I would expect it does more of the shielding but that does not mean the moon hasn’t caught a few on our behalf.

It presumably has.

But if you do the math, you’ll find that statistically speaking it’s in the hundredths of a percent. IOW, negligible.

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**Author:** ![Learjeff](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@Learjeff](https://boards.straightdope.com/u/Learjeff)\
**Post date:** [September 27, 2015, 2:42am UTC](https://boards.straightdope.com/t/asteroid-hits-moon-debris-hits-earth/732439/22 "2015-09-27T02:42:34Z")

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> [@Whack-a-Mole](#):
>
> The reason we do not see impact craters on earth (barring really big ones) is twofold:
> 
> 1. Earth has an atmosphere which burns up the smaller ones before they hit and mitigate the ones big enough to hit
> 
> 2. Erosion. Over time all but the biggest impacts are erased. The moon has no such mechanism (atmosphere or erosion). As such pretty much any impact on the moon surface remains for eons.

Even more significantly,

1. Earth is geologically active, subducting old crust and generating new crust

2. 70% of the surface is under water

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**Author:** ![CCitizen](https://avatars.discourse-cdn.com/v4/letter/c/4af34b/32.png) [@CCitizen](https://boards.straightdope.com/u/CCitizen)\
**Post date:** [September 27, 2015, 3:17am UTC](https://boards.straightdope.com/t/asteroid-hits-moon-debris-hits-earth/732439/23 "2015-09-27T03:17:00Z")

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That is a danger – thousands of times less likely then WWIII.

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