Planet Earth consists of most of the water for the life of all creatures that live on earth. Have you ever imagined where the water supply came from? Did it exist when the Earth was formed or sent from meteorites or space comets?
The source of the earth's water has been a matter of debate. Lawrence Livermore National Laboratory (LLNL) scientists think they have found the answer by looking at rocks from the moon. Their research appears in the Proceedings of the National Academy of Sciences.
Because the Earth's lunar system formed together from the collision of two large objects early in the formation of the solar system, their history is strongly related. The moon is actually a great object to look for clues about the history of earth's water.
Although nearly 70 percent of the Earth's surface is covered in water, overall it is a relatively dry place compared to many other objects in the solar system. According to conventional wisdom, the lack of volatile species such as water on Earth and particularly the moon, is caused by violent impacts that give rise to depletion of volatile elements.
However, by looking at the isotopic makeup of lunar rocks, the research team found the objects involved in the collisions that make up the Lunar Earth system have very low levels of volatile elements. Specifically, the team used the relative amounts of the volatile and radioactive isotope rubidium-87 (87Rb) calculated from its son strontium-87 (87Sr) to determine the levels of Rb in the Earth system of the moon when it formed.
The team found that because of 87Sr, the proxy for the month's long-term volatility was so low that the colliding bodies must have dried up in the first place.
"The Earth was born with the water we had or we were hit by something that was essentially pure H2O. This work removes meteorites or asteroids as possible sources of water on Earth and points strongly toward the origin of water," said co-author Greg Brennecka, a cosmochemist.
In addition to greatly narrowing the potential of Earth's water sources, the study also revealed large colliding objects must have originated in the inner Solar System. Such an event could not have happened before 4.45 billion years ago.
According to Lars Borg, lead author of the study, there are only a few types of materials that can be combined to make the earth and moon and they are familiar. "They may just be large objects that formed around the same area and happened to meet each other a little more than 100 million years after the solar system formed," Borg said.