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Originally Posted by gmku
Someday the sun will explode, too. Then where will we be?
The moon is going farther away from the earth every year. When it gets so far away that it flies out of the earth's gravitational pull, the earth will wobble and there will be catastrophic weather and flooding that will wipe out everything.
Also, a large meteor could cause a huge catastrophe any day, if it hit the earth. The earth would be blanketed in an atmosphere so thick with dust that the sun could not penetrate for years and everything would freeze. This could happen anytime.
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Yes, the sun, like any star, has a life cycle and will one day reach the end of that cycle, many billions and billions of years from now. Our sun has been around about four and a half billion years and only has approximately, per the estimation of astronomers, five billion years left. If this were to happen sooner than expected, we would know about it ahead of time. Through our routine observations of solar activity, scientists would notice the sun heading towards a super-collapsed state.
And yes, the moon is drifting an inch or two away every year. In a billion years or two this will become a huge problem just like gmku described. In addition, the earth's rotation will slow down during this time until eventually a month will last forty or so days. (The earth's rotation is already slowing down slightly because of this as days get a bit longer.)
(On a side note, it's also pleasant to see he, unlike so very many, gmku knows how global warming affects the planet.)
As far an asteroid colliding with the earth, there are so many astronomers watching space these days that we know months or years ahead of time about any bodies that will come close to earth. In preparedness for this eventuality, some contingency plans have already been developed that should be able to divert the incoming asteroid's trajectory just enough to have it miss us. Of course, it was a asteroid that collided with the earth billions of years ago that formed our very proportionately large moon and it is this earth-moon system (along with our mass an distance from the sun of course) that allows for the climate in which we have on earth that is hospitable to humans. And it was, as all know, an asteroid that wiped out the dinosaurs that in turn caused mammilian life to flourish. What many don't know is it probably was a meteorite that also brought life to this planet when protein/animo acids in the impacting meteor interacted with elements on earth and bore single-celled organisms as a result. These strange lifeforms eventually made their way to the sea and we all know what happened from there via biological evolution.