In December 2020, the Chinese mission, Chang’e-5, brought to Earth 1.731 kilograms (3.816 pounds) of lunar rocks. This was the first sample return from the Moon in 44 years and the first analysis shows that the material is much younger than the Apollo samples.
As reported in Science, the samples collected by the Chinese mission date back 1.96 billion years plus or minus 60 million years. Orbital observations have suggested that Oceanus Procellarum – an ancient lava field from a volcanic eruption – was about that age. Aging the rocks has provided precision on those estimates, confirming a young terrain.
“Of course, ‘young’ is relative,” co-author Professor Brad Jolliff, from Washington University in St. Luis, said in a statement. “All of the volcanic rocks collected by Apollo were older than 3 billion years. And all of the young impact craters whose ages have been determined from the analysis of samples are younger than 1 billion years. So the Chang’e-5 samples fill a critical gap.”
Having such confirmation is important for multiple reasons. First of all, it is now possible to study samples from a period in Lunar history that we did not have before. Scientists will better understand the composition of the lunar basalt. The study report that they did not find evidence for high concentrations of heat-producing radioactive elements in the mantle, which was the expected cause for the eruption that delivered this material to the surface. Other explanations will be needed to solve this mystery.
The second important aspect of this paper is that the Moon is used to estimate the chronology of many other bodies in the Solar System. The better we know the ages of terrains on the Moon, the better we can estimate the age of Mars, Mercury, and many other moons and dwarf planets.
“Planetary scientists know that the more craters on a surface, the older it is; the fewer craters, the younger the surface. That’s a nice relative determination,” Jolliff said. “But to put absolute age dates on that, one has to have samples from those surfaces.”
“The Apollo samples gave us a number of surfaces that we were able to date and correlate with crater densities,” Jolliff explained. “This cratering chronology has been extended to other planets — for example, for Mercury and Mars — to say that surfaces with a certain density of craters have a certain age.”
“In this study, we got a very precise age right around 2 billion years, plus or minus 50 million years,” Jolliff said. “It’s a phenomenal result. In terms of planetary time, that’s a very precise determination. And that’s good enough to distinguish between the different formulations of the chronology.”
