The Earth's Memory Is Locked in Ancient Seafloor Muck

By Brian Kahn on at

The Earth does not forget. Meteor impacts, nuclear detonations, Ice Ages, earthquakes: The memories of them all are imprinted in the muck at the bottom of the ocean.

Digging through the sediment layer by layer reveals nearly everything the planet has ever experienced, a veritable history book of life and death on Earth. You just have to learn how to speak in the language of shells, dust, and chemical compounds, which is exactly what Earth scientists probing the muck have learned to do. The memories they translate into English are ones we can all learn from.

Scientists have a few ways to access the planetary memory system, but one ubiquitous technique is through cores extracted from the seabed. To get these cores, they use lower what’s called a piston corer up to five miles below the waves. When it hits the bottom, a piston drives a tube into the mud as far as it will go before the line is drawn back up to the surface. The cores of mud—which are up to 30 feet long—are then brought back to land where they’re stored in archives around the world.

One of the biggest repositories of the Earth’s memories is at Columbia University’s Lamont-Doherty Earth Observatory. There, scientists have been collecting cores for decades. In the 1950s and 1960s, there was a “core a day” policy for the Vema and the Conrad, two research ships that Lamont operated. Both ships travelled over a million nautical miles, which adds up to a lot of cores. Though the policy has died, scientists from Columbia and other institutions continue to send their cores to the Lamont Core Repository, whose archives include some 19,800 samples.

“The entire history of Earth’s climate, over 100 million years, is recorded in these cores,” Maureen Raymo, the head of Lamont’s Core Repository, told Gizmodo. “We know what that looks like, and we can see what’s happening now is not natural, it’s driven by [human] CO2.”

To extract memories from mud, scientists split their cores in manageable chunks, each five feet in length. The piston corer has a PVC pipe insert to keep the goop in place. Those are then split in half, creating two records that scientists can pluck samples from. The cores were originally stored at room temperature, but that caused them to dry and shrink. Still serviceable, but not ideal. Now, all new cores are stored in a refrigerator, which helps keep them in a state closer to fresh modelling clay. All cores are marked and numbered in 10 centimetre increments with the same tabs used to pin your car’s upholstery to the roof.

“They’ve been repurposed,” Nichole Anest, the repository’s curator, told Gizmodo laughing. “We get them luckily in batches of over a thousand so we don’t have to order them very often.”

But while the labels are low tech, the ways scientists analyse the cores is decidedly high tech. Scientists once photographed cores on boats in black and white and used a mix of descriptive words, letters, and numbers called the Munsell Color System to help identify the types of sediment. Now, they use carefully calibrated machines that can image cores in colour, take x-rays, and spin samples. Radioactive signs were all over the equipment and Anest told me I shouldn’t spend too much time standing next to the machines.

I asked Raymo if she had a favourite core. She immediately volunteered an answer: DSDP-607.

“I did most of my thesis on it,” she said. “I generated the first long record of northern hemisphere Ice Ages that show how and where the Ice Ages begin. It’s such a cool site, they went out and re-drilled it 20 years later.”

Claire Jasper, a technician at the lab, told me there’s one core that shows a more recent event. Walking into the refrigerator where all the new cores are stored, she pulled out a smooth pinkish-brown one from a trip to the Caribbean. The core ended in a turbulent jumble of mud flecked with rocks, showing the imprint of the 2010 Haiti earthquake. The frenzied-looking end of the core reflects how the Earth’s shaking jostled sediment and sent underwater landslides cascading into the muck.

These natural events are intermingled with humanity’s imprint. Though not visible to the naked eye, the radioactive legacy of nuclear bomb testing is stored in sediment, too. So are more pedestrian forms of pollution. Hudson River mud shows a spike in lead starting in the early 1900s, which continues until unleaded gasoline was introduced in the 1970s.

And our current carbon polluting bonanza will also leave its mark. Carbon dioxide makes seawater more acidic. The increasingly acidic oceans of today are dissolving and deforming the calcium carbonate shells that tiny sea creatures call forams create. As these creatures die and tumble down to the ocean floor, their shells become part of the Earth’s memory.

“Say in another thousand years if we’re still studying marine ocean cores, it’ll be like ‘oh, what happened there?’” Anest said.

Indeed, even if we get a handle on our carbon emissions, the planet’s memories of our atmospheric polluting spree will last long after we’re gone.

Cores, cores, cores.

Hand-drawn charts showing plotting of the data gathered from sediment cores.

Tiny shells found in cores as viewed under a microscope.