Water on this planet

[Rohando]

I've seen a few documentaries pointing to the fact that it's a possibility that we may have came from another planet on a meteorite, asteroid or comet. They also said that the seas water came from a comet or comets.

Just how many or how big were these comets to have that much water on them and if they were that big why didn't they pummel the earth to bits seeing the earth was just out of a molten state and still soft?

[Nibble]

Since most of the comets/asteroids, etc are remnants from the Late Heavy Bombardment era from 4.1 to 3.8 Billion years ago, then this may help..

http://en.wikipedia.o...ate_Heavy_Bombardment

Specifically..

If a lunar cataclysmic cratering event were truly to have occurred on the Moon, the Earth would have been affected as well. Extrapolating lunar cratering rates to Earth at this time suggest that the following number of craters would have formed..

22,000 or more impact craters with diameters >20 km (12 mi),
about 40 impact basins with diameters about 1,000 km (620 mi),
several impact basins with diameter about 5,000 km (3,100 mi),

Serious environmental damage would occur about every 100 years, although life is not known to have existed on Earth at this time.

[Rohando]

Is this 100% proof that water happened during one of these Heavy Bombardments? Is there any other way or anywhere else water could've came here?

[Huderon]

It seems more likely that rocks which formed the earth and asteroids provided most of the water than that comets were the source.

You might want to read this Wikipedia article http://en.wikipedia.o...gin_of_water_on_Earth and then have a look at this as well http://news.discovery...oid-ice-organics.html

And finally, well there may not be as much water as you think on Earth. Estimates of the volume of water on Europa put it at 2-3 times the volume of water in the Earth's oceans http://apod.nasa.gov/apod/ap120524.html

[bert_h]

As for life arriving here on some impacting object, that wouldn't answer anything either way. If it had arrived here that way, then it must have first originated somewhere else independently, so whatever way it originated there, it could equally well have originated that way here, too.

[wildwood]

Water is just a gas in its colder liquid state.

[Old_Geezer]

Since a comet apparently consists of of ice and dust I have no concerns that such a bombardment could explain how we accumulated water. Or at least be a chunk of the process. (As I understand it asteroids are more rocky.)

Life originating here might be slower to get started than if it had already started elsewhere and crashed into this planet. Thus the suggestion in may have been on Mars first. Heck; maybe the building blocks form in space itself ?

[scowie]

Water doesn't need to come from anywhere to appear on the earth, at least not as water (H2O). Water is created whenever you get hydrogen cations (protons) and oxygen anions in the same place. The solar wind is full of protons so we have a supply of hydrogen cations hitting the atmosphere all the time, hence the aurorae. Oxygen anions can be created by electricity - there is plenty of that occuring in the atmosphere too, i.e. lightning.

Water certainly didn't come from comets because comets are not the "dirty snowballs" they were initially believed to be. All investigations done into comets, i.e. sending probes their way, suggest that they are made of the same stuff as asteroids and have similar origins, i.e. the warmer inner solar system. In other words they are lumps of rock, not ice.
http://www.cosmosmaga...-asteroids-and-comets