4. It was tons of tiny impacts over a very long period of time
about 1,386,000,000 cubic kilometers
Earth is estimated to hold about 1,386,000,000 cubic kilometers of water. The breakdown of where all that water resides is estimated as follows: Oceans (saline) 1,338,000,000 cubic kilometers. Ice caps and glaciers (fresh) 24,064,000 cubic kilometers.
Most meteorites reach the Earth's surface in the form of dust or very small particles after passing through the atmosphere, which is why we do not normally see them. However, believe it or not, some 17,000 meteorites fall to Earth every year.
With clean sampling techniques and accurate ages for dust deposits, the researchers calculated around 5,200 metric tons of micrometeorites fall to Earth every year.
One liter of water weighs about one kilogram. One cubic meter contains about 1000 liters. One cubic kilometer would 1000^4 liters which = 1000^4 kilograms= 1,000,000,000,000 Kilograms that's about a trillion kilograms.
5200 ton = 5,200,000kg
17,000 impacts per year
1,400,000,000 cubic kilometers of water = 1,400,000,000,000,000,000,000kg of water.
If 50% of an asteroid is water, then 2,500,000 kg of water hits the earth every year,
1,400,000,000,000,000,000,000/2,500,000 = 2,692,307,692,308 years.
The universe is only 13,000,000,000 years old.
(Please check these numbers, I may have done some bad maff)
That's not including those that burn up in the atmosphere.
