According to the Hypothesis of Giant Implications, the Earth-Moon system was created about 4.5 billion years ago, when a Mars-sized object collided with Earth. This effect led to the release of massive amounts of material that eventually joined to form the Earth and the Moon. Over time, the moon gradually migrated from Earth and assumed its current orbit.
Since then, there have been regular exchanges between the Earth and the Moon due to their impact on their surfaces. According to a recent study, the impact that occurred during Hadean Eon (about 4 billion years ago) may be responsible for sending the oldest earth rocks to the moon, where it was discovered by Apollo 14 astronauts.
The study, which recently appeared in the magazine Earth and Planetary Scientific Letters, was led by Jeremy Bellucci of the Swedish Museum of Natural History, and included members of the Institute of Moon and Planetary Sciences (LPI), several universities and the Center for Lunar Science and Research (CLSE), which is part of the research on research on NASA's Solar System Virtual Institute.
This discovery was made possible thanks to a new technique developed by the study team for locating lunar regolith impact fragments. The development of this technique was prompted by Dr. David A. Kring, a principal researcher at CLSE and a LPI researcher at the University of Space Exploration (USRA) – to challenge them to locate a piece of land on the moon.
The resulting research led to the detection of a fragment of 2 g (0.07 oz) stone made up of quartz, feldspar and zircon. The rocks of this type are most commonly found on Earth, but are very unusual on the moon. In addition, a chemical analysis revealed that the rock is crystallized in an oxidized system and at a temperature consistent with Earth during the Hadean; instead of the moon, which at that time experienced higher temperatures.
As Dr. Krung says in a recent press release on LPI:
"It's a remarkable discovery that helps to paint a better picture of the wounded Earth and the bombardment that modifies our planet during the dawn of life."
Based on their analysis, the team concluded that the rock was formed in Hadean Eon and was launched from Earth when a large asteroid or comet affected the surface. This impact will have discarded material in space, where it collided with the surface of the moon, which was three times closer to Earth at that time. In the end, this rock material is mixed with the lunar regolith to form a single specimen.
The team can also learn a lot about the history of the samples from their analysis. For one, they concluded that the rock crystallizes at a depth of about 20 km (12.4 miles) below the surface of the Earth between 4.0. and before 4.1 billion years ago, and then it was excavated from one or more events for big shots that sent it to the cis-lunar space.
This is in line with previous research by the team that showed how the impacts in this period – ie. late heavy bombardment (which happened about 4.1 to 3.8 billion years ago) – produced thousands of kilometers of craters, which is more than enough to eject the material from a depth of 20 km (12.4 miles) into space.
They further found that several other influences influenced him after reaching the surface of the moon. One of them caused the sample to partially melt about 3.9 billion years ago and buried it beneath the surface. After that period, the moon was subjected to influences that were smaller and rarer, and gave it the surface that it has today.
The final impact event that affected this sample occurred about 26 million years ago, during the Paleogene period of the Earth. This impact caused a conical crater of 340 m (1082 ft) and dug the sample stone back to the surface of the moon. This crater was the landing site of Apollo 14 a mission in 1971, where the astronauts of the mission received samples of rocks to return to Earth for study (which included rock on Earth).
The research team confirmed that the sample could be crystallized on the moon. However, this would require conditions that have yet to be detected in any lunar sample obtained so far. For example, the sample should crystallize very deep inside the lunar mantle. It is also believed that the composition of the moon in those depths is quite different from what is observed in the rocks of the sample.
As a result, the simplest explanation is that this is an earthen rock that descends on the moon, a discovery that can possibly cause some controversy. This is inevitable, since this is the first Hadean sample of its kind to be found, and the site of its discovery will also probably add the no-confidence factor.
However, Kring predicts that more specimens will be found, as Hadey's rocks are likely to occupy the Moon's surface during a late heavy bomb. Perhaps when crew missions begin to travel to the moon in the next decade, they will have a chance of more than the oldest Earth-rock samples.
The research was made possible thanks to the support provided by NASA's Virtual Research Institute for Solar System Research (SSERVI) as part of a joint venture between LPI and the NASA Johnson Space Center.