Comets, because they are made from ice and dirt.
We do not have a definitive answer to this question. Scientists are still researching this question as of 2015. However, if extraterrestrial, it certainly was not ONE extraterrestrial body.
Meteorites.
Meteorites.
nitrogen is brought to earths surface by the gravitational pull of zero gravity
pressure from the heat under the earths surface
Scientists believe that comets and asteroids may have brought water to Earth's surface. These bodies contain significant amounts of water ice that could have been delivered to Earth through impacts during the early formation of the solar system.
Geologists study the Earths surface
The shifting of Tectonic Plates.
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100
70% or 80% of water covers the earths surface
Comets, many scientists believe. A few, such as British astronomer Sir Fred Hoyle, believed that perhaps organic molecules may have even brought life itself to the Earth in the early days of our planet. This hypothesis, called "panspermia", suggests that the universe might be filled with life spread from only one or a few original locations. So far, this is only an idea; there is no evidence at all to support it. However, since we have conducted only the most cursory examination of a couple of planets and moons in this one solar system, it cannot be completely discounted.