🌋 Lava on the Moon!

you tellin' me there's LAVA on the mOON?

Nov 16, 2023

The other week, I tried to buy a rock and a man told me I was going to go extinct.

Let me explain.

I went to the Geologists Association’s Geology Day at UCL on a Saturday. There was a great talk on the ‘Geology of Hogwarts,’ and trilobites you could drive with a remote control (!?!, sadly, not for adults), and also a few vendors selling rocks and minerals.

I figured I could get something nice for my shelf here, having bought a fossilised fish at the last geological festival I went to. One guy stood behind an array of specimens, with the tiniest little mineral nuggets sitting pride of place at the center of the table. This treasure rainbow had price tags of £100 and upwards. But it was a cheap chunk of olivine basalt that caught my eye.

It probably has 90% to do with the fact that my name is Olivia, but Olivine is one of my current favourites. Olivine is the name of a group of green minerals, all with a similar chemical makeup, and is mainly found in igneous rocks. If you know peridot, this is the gemstone of Olivine.

I don’t know why, because it’s one of the most readily-available rocks in the world, but basalt is also a favourite rock of mine. Maybe because it’s usually black (y’know, like my soul). Maybe because it’s evidence of volcanoes. Maybe because it makes me think of places like Iceland and Hawai’i.

Anyway, my point is, olivine is a mineral which can occur in basalt. So you can get rocks which have both! A 2-for-1!

This is what I spied on the rock seller’s table at Geology Day. A black rock crusted with green crystals. Ooh, so pretty. I leaned over the table.

“Do you take card?”

He turned to me and made a face. “Depends on how much it’s for.”

I told him £10, the price of the pretty basalt which was sitting in front of me.

“Mmmmmm…. no. That’s not really worth it, is it? £25 and up, yes. Not £10.”

Was he talking to me, or himself?

“You not got any cash? See, people stop using cash and then what’s going to happen when all the computers crash?”

This was getting away from me.

“You’re all going to go extinct!” the vendor declared. My boyfriend walked away to stop himself from laughing.

I was starting to get confused and mad. All I wanted was my olivine basalt! “So is it a card minimum issue?” I asked, getting things back on track.

“Oh no, I’ve got the machine right here,” he jerked a thumb over his shoulder. He then started telling me about how he was “not a business” (despite… selling things?) and more of a collector, and wasn’t even expecting people to really buy what he was selling today (despite… the price tags?). I thanked him for his time and walked away.

Leaving the university campus, without my olivine basalt, my boyfriend told he saw the vendor using the card machine for a £15 transaction not long after we’d spoken.

Curse you, rock man!!! I wouldn’t get the olivine today. But one day, ONE DAY, I would get some.

When I went home I did a little google, because I wanted to see if I could write about it for today’s newsletter.

‘Olivine basalt,’ I typed in. And then I found something interesting.

You know there are some very special samples of Olivine Basalt in the world, but they weren’t originally from this world. They’re from… the Moon!

🚀 Great Scott!

Great Scott is a sample of lunar rock from the Apollo 15 mission in 1971. Coming in at a hefty 9.6 kilos, it’s the second largest rock sample delivered to Earth from the Moon, and was the biggest from this Apollo 15 mission. Its proper name is Sample 15555, but ‘Great Scott’ is its informal name, after David Scott who was one of the astronauts on the trip.

There are pieces of Great Scott scattered around the world, one being in the National Museum of Natural History in Washington DC, the Madrid Deep Space Communications Complex in Spain, and even in the Science Museum in London (I am going to have to pay it a visit!).

Sample 15555 cooled around 3.3 billion years ago. What was happening on Planet Earth at this time?

Eh, we were going through something.

Back to the moon.

What’s cool about Great Scott? It’s an olivine basalt. And basalt is igneous, which means it’s a rock that used to be magma.

🌚 Moon Glows, Lava Flows

You know the Lunar Maria? The dark splotches that make up the Man in the Moon? Galileo likened these dark patches to oceans when he looked at the Moon through his telescope, back in the 1600’s. They are actually basaltic lava flows: big plains of cooled lava, covering up much of the Moon’s Earth-facing side.

Quick aside: does ANYONE know what the Man in the Moon is meant to look like? I had a go at trying to find his face in a picture of the moon but I only got this:

Back to lava plains.

Around 3.9 billion years ago, the Moon was getting bombarded by meteoroids, which marked its surface with impact craters. Ouch! Then over time, volcanic activity got goin’, which filled these craters with lava. The basaltic lava flows have been dated between 3.15 and 3.85 billion years ago, so this activity would have taken place over 700 million years. That’s a pretty slow build up! But who said anything was ever fast, in the geologic time?

Have you ever seen the other side of the moon? It looks like this:

Ha ha! Okay, it doesn’t have a butt. But seriously: it look so different! Where’s the lava plains, bro?

Well, scientists think that it’s partly to do with the thickness of the Moon’s crust. Did you know that the crust of the farside (butt side) of the Moon is almost twice as thick as the nearside? This factor seems to be part of the reason why lunar maria didn’t form on the far side: the crust was too thick for lava to seep up through fissures.

🔍 Where are the Volcanoes?

There is evidence of volcanoes, but the moon doesn’t have any big cone-shaped ones, like Mt St Helens or Krakatoa. Because gravity on the moon is just a sixth of what we have on Earth, that means that when volcanoes eject material on the Moon, it would have travelled much further, going ‘weeeee’ and not building up close to the eruption site. Also, most of the material from these lunar eruptions seem to be basalt, which comes from a low-silica lava. This is similar to the lavas you’d find in Iceland and Hawai’i: runny lava which flows freely, not like the violent cloggy stuff you’d find in Stromboli or one of those tall, cone-shaped volcanoes. Lava travelling further = smoother, shallower volcanoes.

But hey, what actually caused this volcanic activity? The Moon doesn’t have any tectonic plates or evidence of there ever being any. And tectonic plates are the biggest generator of volcanoes here on Earth. I honestly can’t say that I found a definitive answer for why these particular lava flows came about during this period, scientists reckon the heat from all those asteroid impacts may have generated enough agitation to cause volcanism during this time, but it is probably also down to the Moon’s own complex mantle activity.

🌋 One More Thing!

Okay, here’s one more cool thing about these lava plains on the nearside of the Moon. They actually affect the Moon’s gravitational field. Their mass is dense enough to create a stronger pull of gravity over them, which is something that NASA discovered with their Lunar Orbiter spacecrafts in the late sixties.

There is so much more to talk about when it comes to volcanoes on the moon. Even now we (I say we, I do not mean we, I mean the scientists, but I just like to feel included) are still figuring out a lot about the Moon, and maybe in 50 years’ time we’ll have to rewrite the textbooks with all the new information we discover.

Only this year did they discover a hotspot on the farside of the Moon!

Maybe we will return to the Moon in another edition of A Constellation. But for now, go look at the Moon (or maybe wait a few days, it looks like a toenail at the mo), and know that you’re looking at lava flows from 3 billion years ago.

📝 Come chat with me in the comments…

Please answer any/all questions in the comments, or just add your own thoughts.

Did you know the lunar maria was actually lava flows? Am I just dumb? Or is this news to you, too?
Are you a chronic moon-starer, too?
Have you ever seen a piece of the moon or touched it? I did at a NASA museum in Houston when I was a kid.
Have you ever seen the Man in the Moon?

a constellation

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