The sample returned by Apollo 14, 48 years ago, contains the oldest Earth Rock discovered till date.

Where would you look for the oldest Earth rock? Probably in the ocean or somewhere underground. As it turns out, the oldest Earth rock was found on the Moon! Yes, you heard it right. An international group of scientists from Center for Lunar Science and Exploration (CLSE) reported that the oldest known Earth rock might have been in a sample returned from the Moon by Apollo 14, 48 years ago. CLSE is part of NASA’s Solar System Exploration Research Virtual Institute (SSERVI). This amazing finding was published in the journal, ‘Earth and Planetary Science Letters’.

Why is the Earth rock on the Moon?

It is believed that the rock broke off the Earth after the planet collided with asteroids. Eventually, the jettisoned rock crashed into the Moon about 4 billion years ago. At the time, the Moon was three times closer to the Earth. The team led by Jeremy Bellucci and Professor Alexander Nemchin found a two-gram fragment of granite which contained quartz, feldspar, and zircon crystals. These materials are all common on Earth but are not found on the Moon. The rock is a type of felsite that can only be created through plate tectonics which is absent on the Moon.

Analysis of the Earth Rock

Further analysis of the Earth rock fragment showed that it crystallized after being oxidized in an Earth-like environment with similar temperatures. On the other hand, the Moon has a reducing environment and high temperatures that would not allow for oxidation. The rock was likely crystallized about 20 kilometers below the Earth’s surface. It may very well be that the crystallized rock was excavated by a large meteorite crash. The free-floating rock eventually landed on the Moon. David A. Kring, a CLSE Principal Investigator, referred to the importance of this discovery by saying,

“It is an extraordinary find that helps paint a better picture of early Earth and the bombardment that modified our planet during the dawn of life. It was confirmation that we had something granitic and that we had large enough impact events to launch things from the Earth. It’s amazing that the rock survived.”

Bellucci further explained the reason why it originated from the Earth. He said,

“If it formed on the moon, it must have formed 167 kilometers (104 miles) deep. Even a massive impact on the moon would not be able to dig up rocks from that far down.”

Is the Evidence enough?

This isn’t the exact proof that the rock is not from the Moon. However, the evidence is quite compelling. Also, the Moon was once part of the Earth before a huge asteroid ejected it out of the planet. It is convincing because, in the early history of our solar system, asteroids were in abundance. Pieces of Mars have also fallen on Earth after they were knocked away in space. It is entirely possible that some of the debris landed on the Moon. Furthermore, the rock is preserved after so many years because the Moon lacks any weather and/or geological processes that would affect the crashed Earth rock. William Bottke, from the Southwest Research Institute (SwRI), elaborated that in the following words:

“Earth’s been hit by a lot of very big things, and it’s conceivable that some of those impacts have ejected material far enough away that it’s been able to escape the clutches of Earth and make it to the moon. What they’ve pointed out is an interesting inconsistency and they’ve pointed out a possible hypothesis, and now we get to figure out whether it holds water or not.”

The Bottom Line

After this discovery, we now have a clearer picture of what the rocks looked like during the early phases of the Earth. Scientists suggest that this isn’t the only rock that got knocked out of our planet. It is also possible that the other rock samples from the Apollo missions contain rocks from Earth too. Kring believes that the scientists will be combing through the other rock samples soon. Only a small fraction of the total 382 kilograms of rocks brought back have been studied so far. On the bright side, the techniques used to analyze these rocks are improving constantly. When we go back to the Moon, searching for more Earth rock samples may be worth it.