A comet impact may have triggered Earth’s ancient warming period

Scientists have discovered the first ever physical evidence that a giant comet or asteroid slammed into Earth around 56 million years ago — the same time the planet went through an abrupt warming period. The timing of the two events is pretty tantalizing for researchers, and seems to suggest that this impact may have been the catalyst for Earth’s ancient temperature rise. And learning more about this past climate change event can potentially help scientists better understand today’s warming climate.

The timing of the two events is pretty tantalizing for researchers

The evidence the researchers found are tiny glassy spheres, known as spherules, inside ocean rocks along the US East Coast. These spherules, detailed today in the journal Science, are thought to be impact leftovers — rock debris that the comet or asteroid ejected when it hit Earth. "There’s never really been any firm physical evidence of that happening," study author Morgan Schaller, an assistant professor for earth and environmental science at the Rensselaer Polytechnic Institute in Troy, New York, tells The Verge. "But this is the first evidence of an impact at this time for sure."

Experts have suggested before that a comet or asteroid impact may have caused Earth’s ancient warming period — known as the Paleocene-Eocene Thermal Maximum, or PETM. The event changed the entire environment of Earth, causing some mass extinctions and turning Antarctica into lush tropical region. The exact cause of the event has been a bit of a mystery, and this new evidence doesn’t solve that puzzle either. But the fact that two such unlikely events occurred around the same time definitely hints at some kind of link between the impact and the rising temperatures.

"This is a major event in Earth’s history, and finding something like this is a major discovery if it holds up," Mark Boslough, a physicist at Sandia National Laboratories in Albuquerque, New Mexico, who was not involved in the study, tells The Verge. "It provides a big clue in the chain of discovery that we need to solve that mystery."

"Finding something like this is a major discovery if it holds up."

The discovery of the spherules came as a big surprise to Schaller and his team, because they weren’t actually looking for evidence of a giant impact at all. Instead they were searching the Atlantic Ocean for tiny single-celled organisms called foraminifera. These fossilized creatures, found in ancient marine rocks, provide a small snapshot of what our planet was like in the past. Researchers can study the chemical makeup of the creatures’ shells and learn about the chemistry of Earth’s ancient oceans and atmosphere.

Images of the spherules found by Schaller's team. (M.F. Schaller et al., Science)

Thanks to foraminifera, scientists have figured out that there was a huge release of carbon dioxide and methane into the oceans and atmospheres 56 million years ago. This buildup of heat-trapping gases caused global temperatures to increase between 9 and 14 degrees Fahrenheit. This warming event is thought to have lasted about 200,000 years.

Instead of finding foraminifera, Schaller and his team found the glassy spherules. Such spherules are believed to form when a huge comet or asteroid sprays droplets of molten rock into the air. These droplets then freeze and fall back to Earth, creating the glassy spheres. Researchers also found another big sign of a past impact in their rock samples: shocked quartz. It’s a form that quartz takes when it has undergone an insane amount of pressure — such as from an impact.

There’s still a lot the researchers don’t know about this ancient event, such as its size and location. The research team only found spherules near New Jersey and Florida, but these glassy objects need to be found in more ocean rocks to see how far the impact debris spread. The impact, however, does seem to be large enough to suggest it could have played a role in the PTEM. "There are a lot of impacts through history, but that it seems to coincide so precisely with this global warming event is a tantalizing coincidence," says Schaller. He says it’s possible that the event triggered super intense magnitude 10 earthquakes, causing the release of methane that had been stored deep within the ocean. Or the impact may have caused a rash of super active volcanoes — big producers of carbon dioxide.

Learning more about this time period is crucial for us, since we’re experiencing our own global warming period

While there’s still a lot left unanswered, learning more about this time period is crucial for us, since we’re experiencing our own global warming period. And both climate events seem to be caused by a significant buildup of CO2 and other greenhouse gasses in the atmosphere. Carbon dioxide levels are thought to have reached around 1,000 parts per million (ppm) during the PTEM, while current levels are at 400 ppm. "There are a lot of control knobs on Earth’s temperature," says Boslough. "But the biggest control knob of all that’s been shown is the amount of CO2 in the atmosphere."

Today’s rising temperatures have been linked to human activities, of course, such as the burning of fossil fuels. But the scope of the current global warming and the one that occurred 56 million years ago aren’t too far off from one another. Global average temperatures have increased by about 1.4 degrees Fahrenheit since 1880, according to NASA. And if things don’t change, experts only predict those temperatures to get worse. "Epic changes in Earth’s history were caused by asteroids, and the current one is caused by humans," says Boslough. "So if you look at the geologic history, you should probably compare us to the asteroid."