Earthly Water
About 4.5 billion years ago, the blue planet was still red-hot and anything but blue. It was only much later that it earned its current nickname thanks to its vast oceans. But where did all the water come from?
If it's supposed to be romantic on TV, the director likes to choose a picturesque sunset by the sea as a backdrop: the sun, puffed up into a huge ball of fire, merges with the ocean on the distant horizon and bathes everything in a soft orange-red. The last rays of sun sparkle on the calm waters. The soft sound of the sea accompanies the scenery.
Inconceivable if there were no oceans on our planet - also in real life. The ancestors of today's oceans are believed to have formed from water that was already on Earth. It was contained in the raw material from which our earth was formed. Enclosed in the rock, it was able to escape from the interior of the earth through the initially still liquid magma. Initially, it completely evaporated. However, as the earth cooled and a crust formed, water was gradually able to accumulate over millions of years. The first primordial oceans were formed. Or was it just primordial pools?
In fact, scientists doubt that all of today's water comes solely from the earth's interior. Reason for skepticism is the assumption that the young Earth was under intense bombardment from comets and asteroids. Impacts were much more common in the early solar system than they are today. Explosions with the strength of countless atomic bombs repeatedly shattered the cooling earth. Large parts of the accumulated water could have escaped into space. Some even believe in complete drainage.
Comets may have played a more constructive role in the evolution of the planet, however. As celestial impacts diminished and the Earth continued to cool, they may have brought water to Earth, forming the oceans.
What sounds like science fiction can even be verified: the isotope ratios in the ice of the comets could be the key to the truth. If the ratios of deuterium to simple hydrogen matched those of the Earth's oceans, this would be a strong indication that the theory is correct.
So far, however, comets have always contained more deuterium than our oceans. This does not mean, however, that the comet theory must be rejected immediately. The icy celestial bodies could have formed in different regions of the solar system and thus have different heavy water contents. So there may be comets with the right water composition. In 2001, researchers thought they had found such a candidate in comet LINEAR. Unfortunately, it fell apart before a final analysis was possible.
The Rosetta space probe, which is set to be the first probe to land on a comet's surface, should provide deeper insights into the composition of a comet. However, it will not be installed on 67P/Churyumov-Gerasimenko until 2014, in order to determine, among other things, the isotope ratios in the ice. Perhaps she can bring the mystery of the origin of earthly water a little closer to the solution.
In addition to water, the scientists are also interested in the other components of a comet. In addition to ice, rock and lots of dust, complex organic molecules have been discovered in comets. It is controversially discussed whether these could have reached the young earth together with water through comets. The molecules rich in carbon, oxygen, hydrogen and nitrogen could then have laid the basis for life on earth. But that's another and much more speculative story.
