Scientists say they have discovered the oldest rock on Earth in a lunar sample returned from the Moon by the astronauts of Apollo 14.
An international team associated with the CLSE in the United States found evidence that the rock was fired from the Earth by a large asteroid or comet.
This effect ejects the material through the primitive atmosphere of Earth, into space where it collides with the surface of the moon – three times as near Earth as it is now – about four billion years ago.
Subsequently, the scale is mixed with other lunar surface materials in a single sample, according to a study published in Earth and Planetary Science Letters.
The team developed techniques to locate fragments of moon regoliths that led CLSE Chief Research Officer David A Kring to challenge them to find a piece of Earth on the Moon.
Researchers have discovered a fragment of two grams of stone made of quartz, feldspar and zircon that is often found on Earth and is very unusual on the moon.
The chemical analysis of the rock fragment indicates that it crystallizes in an Earth-like oxidized system at land temperatures rather than in the reducing and higher temperature conditions of the Moon.
"This is an extraordinary find that helps paint a better picture of the early Earth and the bombings that have changed our planet at the dawn of life," said Kring, a scientist at the University of Space Research at the Institute of Lunar and Planetary university,
It is possible that the sample is not terrestrial but crystallized on the Moon, but this would require conditions that have not been derived from the lunar samples so far.
The specimen is required to form at great depths in the moon's mantle, where many different rock compositions are expected, they say.
The simplest interpretation is that the sample has come from the Earth, according to the researchers.
The rock crystallized about 20 kilometers below Earth's surface from 4.0 to 4.1 billion years ago.
It is then excavated by one or more major impacts and placed in the lunar space.
The team's previous work has shown that impacting asteroids at that time produced craters thousands of kilometers in diameter on Earth large enough to bring material from these depths to the surface, researchers say.
Once the sample reached the lunar surface, it was affected by several other events, one of which was partly melted 3.9 billion years ago and probably buried beneath the surface.
Hence, the sample is a remnant of an intense bomber period that shapes the solar system for the first billions of years.
After this period, the Moon is affected by smaller and less frequent impacts.