We now have the evidence that Lava was still flowing at the Moon's surface 1.97 billion years ago. This new work, which was published in Science by an international group of planetary scientists of which we are a part, is the result.
We have been working with scientists from Australia, China, Sweden, the USA, and other countries to study samples taken from the Moon by China's National Space Agency during Chang'e-5.
Chang'e-5, an uncrewed mission that included a robotic lander and landed on December 2020 (the Earth-facing side), was uncrewed. The lunar rocks were the first to be collected from the Moon since 1976, when the Soviet Union's Luna 24 mission was launched.
The Chang'e-5 mission had one goal: to discover evidence of some of Moon's youngest volcanic eruptions.
Scientists have been able to predict the age of volcanic rocks on the Moon in the past by looking at the impact craters. However, this cannot be confirmed without samples.
The sensitive high-resolution, ion microprobe SHRIMP (SHRIMP Center) was used to analyze the samples.
The material was first sorted. For investigation, our colleagues in China hand-picked small fragments of basalt (a volcanic stone) approximately 2 millimeters in size (0.08 inches). Following this, laboratory analysis was performed using the same techniques that were used to analyze the Apollo 1 samples in the 1970s.
Although the process of determining age of rocks was complicated, it was simple. We used a concentrated beam of charged particles to eject material in various minerals from the rocks, and then analysed the material.
Our efforts paid off when we were able determine the eruption age of these lavas at 1.97 billion year, which is a billion years earlier than any basaltic lava previously dated from the Moon.
A new scientific mystery
Over its geological history, many volcanic eruptions have occurred on the Moon's surface, creating large sheets of basaltic rocks, known as the lunar mare. These are visible as dark spots looking up at Moon.
Most volcanic activity happened between 3-4 billion years ago. This has been confirmed by planetary scientists who have dated basalts taken from the Apollo and Luna rock collections as well as meteorites which originated from the Moon.
However, the prediction of younger volcanic rocks based on crater counting studies has remained elusive until now.
To trigger volcanic eruptions, heat must be generated on the planet's surface to create the molten material.
It is believed that the heat from an Earth the size of the Moon would have been lost before the eruptions 2 billion years ago.
This research has opened up new scientific mysteries about how a tiny rocky planet body like the Moon could have maintained enough heat to continue producing volcanic explosions 2.5 billion years after its formation 4.5 billion year ago.
What's the explanation? Scientists have suggested previously that radioactive elements could have melted the Moon's rocky material, but the composition of these samples suggests otherwise.
It is not clear if so-called "tidal heating" could have played a part. This was where heat was generated within the Moon's inner by stretching and squeezing (think about an elastic band warming up through friction and being stretched) due to gravity between Earth and Sun.
Alternativly, it could be that the Moon's unique mantle composition resulted in lower melting temperatures, explaining why the molten material formed.
The samples are being developed to answer this question.
The Apollo missions' samples were used to revolutionize our understanding of the Solar System's dynamic and how planets form and change. This new study once again demonstrates the scientific value of receiving samples from other planet bodies in order to decode their secrets in Earth-based laboratories.
Validating the crater counting method with lunar samples has important implications for dating other planets where we haven’t yet collected samples (e.g. Mars, Venus, or Mercury).
It will improve our understanding of the Solar System.
Joshua Snape is a Royal Society University Research Fellow at the Department of Earth and Environmental Sciences at University of Manchester. Katherine Joy is a Royal Society University Fellow / Reader at School of Earth and Environmental Sciences. Romain Tartese is a Senior Research Fellow at the Department of Earth and Environmental Sciences University of Manchester.
This article was republished by The Conversation under Creative Commons. You can read the original article.
