(ORDO NEWS) — No one on earth can live without water. Thus, the origin of water on Earth is the source of life in the solar system (and universe) as we know it.
Figuring out when and how our world got its water may be the key to finding life on other worlds, but the truth is we don’t know exactly where it came from.
However, it is generally accepted that one possible mechanism for delivering water was bombardment by water-bearing asteroids and comets when the Earth as we know it today was much younger.
But a new analysis of rocks collected from the Moon and brought back to Earth shows that this may not actually be the case.
Rather, according to a team of researchers at Lawrence Livermore National Laboratory, the most likely explanation is that the Earth formed with water. In other words, the water has been here all along.
“Earth either came into existence with the water that we have, or we were hit by something that was mostly pure H2O,” explains space chemist Greg Brenneca of LLNL.
The moon may seem like an odd place to look for Earth’s water. However, as it turns out, the Moon is a great place to study the history of the Earth.
The Moon was formed when two massive objects – one about the size of Mars, the other slightly smaller than our own world – collided with each other and formed into blobs that would become the Earth and its Moon.
Earth’s memory of the event has faded over time, but since there is no plate tectonics or weather on the Moon, geological evidence does not disappear in the same way.
This does not mean that there are no processes at all. The impact of other space objects and previous volcanic activity can change the lunar surface. However, in the Apollo collection there are several samples that have not changed much.
Now, according to the giant impact hypothesis, this collision 4.5 billion years ago actually drained the Earth and the Moon.
That is why the Moon is so dry in this model; and, compared to other objects in the solar system that have water, most of the Earth is also quite dry, especially when you take into account its size.
To understand the history of the Earth-Moon system before the collision, the team studied three lunar samples that crystallized between 4.3 and 4.35 billion years ago by studying two isotopes: the volatile and radioactive isotope rubidium-87 (87Rb) and the isotope it decays into strontium -87 (87Sr).
The latter is especially considered a good indicator for understanding the long-term volatile balance of the Moon, and the relative abundance of moderately volatile elements such as rubidium reflects the behavior of more volatile substances such as water.
This means that the different distributions of volatiles on Earth and the Moon were inherited from Earth and Theia, which could explain why the Earth is wetter.
It also suggests that both bodies probably formed in the same general region of the solar system rather than Theia formed further and migrated inward, and that the collision could not have occurred earlier than 4.45 million years ago.
The scientists say that while the study challenges some conventional wisdom about the formation of the Earth and Moon, it accurately explains the origin of volatiles in the Earth-Moon system.
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