The moon is apparently pockmarked and asteroids hit the earth a lot too but we have been here there have been few. It has to happen sometime hey. The atmosphere protects us somewhat from the smaller ones because they burn up.

SOB

Crapageddon more like it 

Emma wrote on Feb 12^th, 2013 at 1:30am:



An asteroid could hit the earth at any moment & wipe out all human civilisation.
Still - that is very unlikely to happen in anyone's lifetime.
I think we get a large hit about every 60 million years.

Quote:


A. Has the presence of the moon through the ages meant that the Earth was...

1.less exposed to meteoroid impact (because they hit the moon instead or were subject to the slingshot effect of the moon's gravity),

2. more exposed (because of the larger gravitational target)
or

3. There was no net difference because the two effects cancelled out.

In your answer, take into account that the Moon's orbit  has gradually drifted away further from the Earth and that the numbers of meteoroids decreased dramatically in the first billion years of the solar system.

B. Develop an iterative, multi-variable hillclimbing based  algorithm to demonstrate that the meaning of life is actually 42.

(Show all calculations)   

That's what I think too, yet for a while a few astronomers were claiming that the presence of the moon resulted in more cometary impacts in the early solar system and was largely responsible for the thickness of the Earth's atmosphere today. (from comet captures and collisions).

The gravitational profile was also greater when the moon was closer to the Earth, which happened to be at the time when cometary collisions were more likely. In other words, the Earth and Moon acted as a more effective comet catching system when they were closer together.
 
This brings us to the fact that early comets had a central heating system powered by Aluminium 26. So we have comets containing methane, carbon dioxide and  possibly liquid water together with a radiogenic heat source which could produce large combinations of organic chemicals.

In other words  - were comets the seeds of life?

An interestng thought at least.

perhaps the Earth is somewhat protected from meteors and asteroids , by the presence of the Moon ..as you 've commented,  different gravitic forces are at play..

But there is plain evidence, all over Earth that shows some truly massive impacts in the past.

The Australia continent presents a fascinating picture of past strikes.

I read a particularly riveting article in Australian Geographic,  within the last yr or so,.. which mapped our most significant impact sites,  and when they occurred.

Fascinating... Humbling... 

Worth checking out.

Bobby??

I don't think you can compare an asteroid with a comet,  in the context of orbit.

an asteroid or comet could be put off it's usual safe course
& end up on a collision course with earth -  many orbits later.

I may be wrong,  but just off the top of my head.... 

Comets are known to be on basically elliptical orbits,..... but not around Earth..

Their transit has nothing to do with Earth. We just happen to be on the way.

Asteroids, big and small,  captured in the belts that surround planets in our system...  may degenerate over time..and go down the gravitational well...   but it'd take a long time.!! Our science should be up to noticing these  ..hopefully.

but I don't think the Asteroids we are talking about have any orbit based on Earth. Have they?

Aren't they  the 'free radicals' of the perceivable universe??

and as a part of the swirling galactic arm that includes the Milky Way... 

is not our outpost moving closer to an area of much denser matter..eg asteroids... 

I KNOW I'm talking galactic time......  but sooner or later.. if we continue to exist,... this will present a much greater danger to our civilisation.

If WE are now just approaching that area of space ...who can say how much more frequent this 'missed by a whisker' event will be.??

Definitely food for thought.

..