According to one of the most popular models of the formation of the Moon, a natural satellite of our planet could appear as a result of the collision of a certain cosmic body with the Earth more than 4.5 billion years ago. This body was Theia, a protoplanetary object with the "embryo" of the Earth. The collision led to the release of the matter of Theia and proto-Earth into space, and from this matter the Moon was formed, which explains its amazing geological and chemical similarity to our planet. As part of the new study, scientists tried to understand in more detail what was the further fate of our satellite after this event.
During the period of the Katarchea (geological aeon), the Moon did not look at all the way it looks today. It was rather a red-hot lava lump with an exotic superdense atmosphere of silicon and metal vapors. It was also located 10 times closer to the Earth's surface than it is today.
During the study, the team of scientists came to the conclusion that one of the features of the Moon may indicate that the Earth was deprived of oceans of liquid water during the first 400-500 million years of its existence. And such conclusions, in turn, impose serious restrictions on the time of the origin of life on Earth. Scientists have shared their work in the journal Geophysical Research Letters.
As is now commonly believed, in the next few million years after its formation, the Moon quickly moved away from the Earth as a result of the action of tidal forces, until eventually it entered the orbit in which it is today. Subsequently, when the Moon began to always look at the Earth with only one side, this process slowed down sharply, and now it is moving away from our planet at a rate of about 2-4 centimeters per year.
Zhong and his colleagues uncovered one unusual detail of this process, drawing attention to the most mysterious feature of the moon - its unusual "hump" located at the equator. This structure was discovered by the French astronomer Pierre Laplace two centuries ago. Laplace noticed that the Moon was "flattened" about 17-20 times stronger than it should have been, given the speed of its rotation around its axis.
"The lunar equatorial hump may contain secrets of the early history of Earth's evolution that we did not even know about," says researcher Shijie Zhong of the University of Colorado in Boulder (USA).
Researchers believe that the existence of this structure indicates that in the distant past, the moon rotated much faster than today. American planetary scientists tried to understand how quickly the Moon "slowed down" by studying how this "hump" works and trying to reproduce its appearance using a computer model of the solar system's development.
These observations unexpectedly showed that the generally accepted theories about the rapid deceleration of the Moon in the early years of its existence were erroneous - the rotation speed of the Earth's satellite remained high for at least the first 400 million years of its existence. Otherwise, the Moon would always remain a "liquid" planet or have a completely different shape and size than it is today.
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Such a scenario, as Zhong explains, is possible only if the Earth was not at that time covered by an ocean of water comparable in size to the planet's current hydrosphere. This means that there was no liquid water on the young Earth. She was either absent on it in principle, or was brought after the formation of the "hump" of the moon, or was on it in a solid form, that is, in the form of ice.
“The Earth's hydrosphere, if it existed at that time, was completely frozen, as a result of which the tidal forces practically did not“slow down”the Moon. The probable reason for this, we believe, may be that the sun was not as bright then as it is today,”says Zhong.
Such conclusions put serious restrictions on the time of the appearance of life on Earth and make scientists doubt the recent statements by geologists that the first living organisms could have appeared on our planet as early as 4 billion years ago.
Nikolay Khizhnyak