Hello and welcome to our semi-regular roundup of interesting articles in the Earth Sciences! Today, in honor of the moon passing between the Earth and the Sun down in South America, causing a whole lot of very cool visual effects, I figured we'd rummage through the moon-related links I've been collecting and see what our closest neighbor is up to.

But wait! you say. Dana, this is earth science time. And the Moon is an astronomical object!

Of course it is! But look at it this way: Earth and Moon form two parts of one system, and also, there's geology up on that thar space rock. So it counts. The earth sciences can extend to anything with a rocky surface - and even beyond.

But okay. We'll begin with a bit of something that's very probably Earth, even if it did end up plunked down on the surface of our satellite.

Apollo Astronauts May Have Brought a Piece of Ancient Earth Back From the Moon

A re-analysis of lunar materials collected during the Apollo 14 mission has resulted in a rather astonishing conclusion: One of the rocks brought back appears to contain a small chunk of Earth dating back some 4 billion years. Incredibly, it’s now amongst the oldest terrestrial rocks known to exist.

New research published this week in Earth and Planetary Science Letters is claiming that a rock fragment embedded within lunar sample 14321—a two-pound rock known as Big Bertha—is of terrestrial origin.

How awesome is that? You know how hard it is to find four billion year-old pieces of Earth on Earth?! A find like this is pretty epic, and can help us understand what our planet was like back in its early years.

And here's some pretty neato stuff going on during a recent lunar eclipse:

Holy Crap, the Moon Was Struck by a Meteorite During the ‘Super Wolf Blood Moon’ Eclipse

As the January 21 eclipse unfolded, however, some observers noticed a tiny flash while watching the online broadcasts, reported New Scientist. Some suspected the flash was caused by a meteorite strike—and it turns out they were right.

To me, that is one of the neatest things ever. And it's how astronomy becomes geology, right there on another world!

Here is a cool new study on moonquakes: did you know the Moon is actually shrinking?

Apollo-era Data Reveal Moon’s Tectonic Activity

The presence of tectonic activity doesn’t mean that the Moon has plate tectonics — its crust isn’t broken into a patchwork of moving plates like Earth’s crust is. Instead the Moon, like most rocky bodies in the solar system, has a single plate that covers its whole surface. On Earth, the inevitable loss of heat from the interior drives its plates’ movements, but it’s a different story on these one-plate worlds: They contract as they cool down, forcing their rigid crusts to adjust. The Moon’s surface wrinkles as it’s compressed, forming thrust faults when the crust breaks. One side of the break slips downward while the other side goes upward, a process that creates telltale steep slopes, or scarps, across the Moon that are typically tens of meters high.

This has implications for where we should site lunar bases, if we ever build them. And, I mean, quakes on another world! Intriguing stuff!

We're also finding Moon water that moves! But it's a very different kind of movement than you might expect:

The Moon Has 'Moving Water,' but Don't Break Out Your Swimsuit

NASA’s Lunar Reconnaissance Orbiter (LRO), a probe that has orbited the Moon since 2009, spotted water molecules being absorbed and released from grains of dust on the lunar surface throughout the day, based on the temperature. These results mark the only dataset recording the distribution of water during the lunar day, according to the paper published in the journal Geophysical Research Letters.

[snip]

The new study, led by Planetary Science Institute senior scientist Amanda Hendrix, analyzes data taken by the Lyman Alpha Mapping Project (LAMP), an instrument that measures far-ultraviolet light on the Lunar Reconnaissance orbiter. The researchers analyzed the daytime variations of ultraviolet light reflected by the lunar surface from 2009 to 2016. Their results showed a tiny amount of water molecules migrating around the Moon based on the temperature, where the rocks release the most water around noon when the temperature is highest and the water moves to areas with less incoming solar radiation.

An itty-bitty water cycle, maybe! Hydrogeologists will be delighted to find work on the lunar surface!

Meanwhile, on the far side o' the Moon:

Chang'e-4: Chinese rover 'confirms' Moon crater theory

The Chinese Chang'e-4 rover may have confirmed a longstanding idea about the origin of a vast crater on the Moon's far side.

The rover's landing site lies within a vast impact depression created by an asteroid strike billions of years ago.

Now, mission scientists have found evidence that impact was so powerful it punched through the Moon's crust and into the layer below called the mantle.

Chang'e-4 has identified what appear to be mantle rocks on the surface.

It's something the rover was sent to the far side to find out.

This is a super-exciting time to be an earth scientist, because we're no longer mostly limited to earthbound observations. Rover geologists are performing all sorts of work and sending the data back, and someday possibly soon, we'll be sending people to hit some other-worldly rocks with hammers.

Who woulda thought geology could be out of this world?