Miniseries: The Oldest Rocks in Antarctica

Hello, and welcome to Bedrock, a podcast on Earth’s earliest history.

I’m your host, Dylan Wilmeth.

These next few weeks, I’m off on summer break, so we’re doing something different on the show. We’re going to take a quick tour around the Earth in seven weeks. Our destinations will be the oldest rocks on each continent. Seven weeks, seven continents.

These locations will be very important in upcoming seasons, so think of these episodes like teaser trailers. Hopefully when we’re all done, you’ll want to learn more. If you want to follow along at home, we’ll have geologic maps of each continent on our website: bedrockpodcast.com

The rocks on this series only cover 5% of the Earth’s surface, but represent the first half of Earth history. Some continents have a lot of ancient rocks, some very few. Some contain the oldest fossils on Earth, while others remain understudied and mysterious, perhaps none more so than our first continent on the list. Break out your maps, it’s time to visit Antarctica.

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You might not be familiar with Antarctica’s geography, since most maps have it strung out like a skirt on the bottom of the world. For this episode, I would recommend finding a map that’s centered on the South Pole.

*Geologic map of Antarctica. Pink rocks are Precambrian (> 500 million years old). Modified from Matsuoka et al., 2018.*

To me, Antarctica looks like a giant white rubber duck, just like one floating in your bathtub: there’s a small head sitting on a big body. The head is in the Western Hemisphere, so it’s called West Antarctica. This is the pointy bit that sticks up by South America. There are plenty of rocks in West Antarctica, but these are only as old as the dinosaurs, more than ten times younger than what we’re looking for.

Sandwiched between east and west are the Transantarctic Mountains, the backbone of our rubber duck. This is where we see the famous volcano Mount Erebus, and the largest community on the continent, McMurdo Station with 1,000 people. Many famous and infamous polar expeditions dealt with these moutains, but not ours. Like West Antarctica, most of the mountains are too young for this podcast.

On the other hand, there’s East Antarctica, the giant body of the rubber duck. East Antarctica is the size of China. More than 90% is covered with ice, including the famous South Pole. Most of the rocks are within spitting distance of the coast- the ice is just too thick farther in. However, the rocks we do find are much, much older than the west.

The oldest rocks in Antarctica are just below the Indian Ocean- if you traveled straight north you would hit Madagascar. If you’re looking on a map, you’ll notice a large but narrow inlet around 70 E- that’s where X marks the spot.

*Garnet gneiss from Enderby Land, Antarctica, ~3.8 billion years old*

These rocks are called the Napier Complex, and it’s around 3.8 billion years old, March 1st on the Earth Calendar. For context, Season 1 ends around mid-February, so these rocks are just around the corner. Even for researchers like myself, 3.8 billion is really old- there are very few places left from that time. They’re even older than the oldest fossils, though some people would fight me on that. In fact, there are probably folks who fight me on every sentence in this episode. Such is the nature of Precambrian research.

These rocks have been pressure-cooked above 1000 C, twice as hot as a tandoori oven. This might sound odd for Antarctic rocks sitting beside giant ice caps but remember- this cooking happened a long time ago, much deeper below the Earth’s surface. In the business, we call these metamorphic rocks- they have been changed or metamorphosed from something else. The original rock was granite like your kitchen countertop. The new rock is called gneiss, if you want to learn more about how to make a gneiss, check out Episode 2.

The Napier Complex is just like its’ name suggests: complex. There are younger rocks mixed in with the older ones, all of them have been heated and changed to something else. Recent evidence suggests the whole complex is recycled from rocks 4.4 billion years old. Long time listeners of the show might get excited at that number- it’s the same age as the oldest stuff on Earth, our old friends the Jack Hills zircons in Western Australia. In fact, all the stories I have just told you come from Antarctic zircons- they’re one of the few things that can take the heat.

There are a few other patches of slightly younger rock in the area, but their stories are still unfolding. At the moment, we know they’re less baked than the Napier Complex, but that’s not saying much.

Still, if you’re an adventurous tourist, could you visit these rocks? Not really. These places are remote even by Antarctic standards, on the other side of the continent from the famous destinations like the South Pole, McMurdo, and the Antarctic Peninsula. Still, there are some permanent research stations out there, each with a fascinating story. China has Zhongshan Station, which almost didn’t exist. The first ship was nearly capsized by falling ice and was trapped by icebergs for seven days. Their window of escape was less than two hours and 30 meters wide, but in 1989 they finally made landfall. Also, the ship which serves the station is called the Ice Dragon, which is just impossibly cool.

Davis Station is Australian, but the first folks to land there where Norwegian whalers in 1935, including Caroline Mikkelsen, the first woman to set foot on Antarctica.

Finally, there’s Mawson Station, the closest to the Napier Complex. It’s the oldest continuous station south of the Antarctic Circle, established in 1954 by the Australians. The station is named after an Australian geologist: Sir Douglas Mawson. Mawson has a storied career in Antarctic exploration: with Ernest Shackleton in 1908 he was on the first team to reach the South Magnetic Pole and the summit of Mt. Erebus, the tallest volcano on the continent. But his most harrowing adventure would come four years later.

It's December 14, 1912 on the coast of East Antarctica. Three men have been trudging across glaciers for a month with a pack of sled dogs: Mawson the leader, Mertz the ski expert, and Ninnis the Royal Lieutentant. The men are five hundred kilometers away from their base when suddenly Ninnis in the rear is missing. He fell through an ice sheet covering a crevasse 3 meters wide. Mawson and Mertz could see the dogs more than 50 meters deep, 150 feet. Ninnis must have fallen even farther.

Low on supplies, Mawson and Mertz turned around and started the long journey back, spending Christmas and New Year’s marching home. Three weeks later, Mertz grew ill and died along the way. Mawson was now completely alone, there were no more dogs. He would have to haul back the rest of the gear himself across 160 km of Antarctic wilderness. It took him another month, making ice shoes from wood and nails after unspeakable things had happened to his feet.

When Mawson returned to camp on February 8, he was revived by a small rescue team, but the ship back to Australia had left just hours earlier. It would not, could not return for nearly another year.

Mawson would keep exploring Antarctica for decades, including the Napier Complex, the oldest rocks in Antarctica. Many other geologic features would be named after him including a huge area called the Mawson Craton, or more whimsically, Mawsonland. When scientists look at rocks from Mawsonland, they are surprisingly similar to stones across the sea in South Australia. In fact, if you pull the two continents together, the rocks would match beautifully like pieces of a jigsaw puzzle. If you want to learn more about that story and another polar explorer, check out Episode 11.

Speaking of Australia, that’s our next destination on the Grand Tour. Unlike Antarctica, Australia has many more ancient rocks to explore, and they are far more pristine. Next episode, we’ll take a look around the Outback at the oldest minerals, the oldest lakes, and the oldest fossils on Earth.

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Thank you for listening to Bedrock, a part of Be Giants Media.

If you like what you’ve heard today, please take a second to rate our show wherever you tune in- just a simple click of the stars, no words needed unless you feel like it. If just one person rates the show every week or tells a friend, that makes us more visible to other curious folks. It always makes my day, and that one person could be you. You can drop me a line at bedrock.mailbox@gmail.com. See you next time!

Images:

Antarctica Geologic Map: modified from Matsuoka et al., 2018: https://i.redd.it/4zbaz4fgw5b81.png

Garnet Gneiss: https://commons.wikimedia.org/wiki/File:Garnet_gneiss.jpg

Mawson photo 1: https://commons.wikimedia.org/wiki/File:Douglas_Mawson_1914_1.jpeg

Mawson photo 2: https://commons.wikimedia.org/wiki/File:Douglas_Mawson_recuperating.jpg

Music:

Miniseries: The Oldest Rocks in Australia