The high-energy impact of about 100 million years after the formation of our solar system caused the two colliding planetary objects to merge into one another to create the Earth-Moon system we now have. An international team of researchers, led by an open-university scientist, found that most of the earth's water was present before the catastrophic impact and was not later delivered by small asteroids and comets, as previously thought. This suggests that liquid water can withstand huge impacts and be abundant on exoplanets, making life outside the solar system more likely to exist.
It is believed that a collision of two protoplanets with unique isotopic compositions created the Earth-Moon system. But explaining why the Earth and the Moon do not have unique isotopic properties like most planets in the Solar System itself was a challenge.
To remedy this, some scientists have proposed a high-energy collision model Isotopes between the two were almost equally mixed on impact; Later effects on the rock planets could have come later.
To better understand the likelihood of this scenario, Open University researcher Richard Greenwood and co-authors compared the oxygen composition of the returned lunar rocks from all six lunar NASA Apollo landings with volcanic rocks from the seabed here on Earth.
The team discovered only a small difference between the lunar and the natural rocks.
"Our analysis showed a 3 to 4 ppm (parts per million) difference between the oxygen isotope concentrations of the lunar rocks and the terrestrial basalts, but no significant difference between the lunar samples and the terrestrial olivine, a common mineral in the soil", the scientists explained.
"This shows how efficiently the two colliding planets are mixed, and also places strict limits on the types of material that could later be added to the Earth."  "If most of the water on Earth had arrived after the collision, we would expect the lunar and earth rocks to have significantly different oxygen compositions, suggesting that liquid water on Earth is at an earlier stage must have existed before the moon-forming influence. "
" Because water is such a vital part of life, we rightly consider it precious, "Dr. Greenwood
"Our research shows that water is also extremely resilient and can weather an event as catastrophically as two planets collide."
"What is even more intriguing is that because it worked for the Earth and the Moon, it also works for planets beyond our solar system, and exoplanets with water on their surfaces can be much more common than we thought before, and where Water is, could also be life. "
The research is published in the journal Science Advances .
Richard C. Greenwood et al. . 2018. Oxygen isotopic evidence of the accretion of Earth's water from a high-energy, moon-forming, giant impact. Science Advances 4 (3): eaao5928; doi: 10.1126 / sciadv.aao5928