A new study shows that a massive impact event occurred at the end of the Ice Age, triggering global climate change that altered the history of life on Earth. The team of researchers found evidence of 10 Million tonnes of impact spherules that were deposited across four continents 12,800 years ago. "Impact spherules" are formed by material that is melted, tossed into the air by an impact, then solidifies and falls back down to Earth.
“Imagine living in a time when you look outside and there are elephants walking around in Cincinnati. But by the time you’re at the end of your years, there are no more elephants. It happens within your lifetime.”
- Kenneth Tankersley, assistant professor of anthropology and geology, University of Cincinnati
An environmental scanning electron microscope image of a carbon spherule from Sheriden Cave. Credit: University of Cincinnati
The University of Cincinnati’s Ken Tankersley used excavations at Sheriden Cave in Wyandot Ohio in his research on the Younger Dryas. Credit: The University of Cincinnati
“We know something came close enough to Earth and it was hot enough that it melted rock – that’s what these carbon spherules are. In order to create this type of evidence that we see around the world, it was big,” - Tankersley
The Younger Dryas is also known as The Big Freeze. It's a relatively short geological period that occurred between about 12,800 and 11,500 years ago. Before the Younger Dryas (about 12,000 years ago), the Earth was at the peak of the Ice Age and it was starting to warm up gradually. However, something dramatic happened and caused this warming to quickly change course. The Earth was plunged back into a near-glacial climate.
Geologist Kenneth Tankersley from the University of Cincinnati has been exploring a cave in Ohio - Sheriden Cave in Wyandot County - which gives him access to geological layers that date back to the Younger Dryas. Here, he found spherules that indicates that an object approached the Earth close enough to melt rock. Similar spherules have been discovered at other sites around the world.
The Younger Dryas Boundary strewnfield shown (red) with YDB sites as red dots and those by eight independent groups as blue dots. Also shown is the largest known impact strewnfield, the Australasian (purple). Credit: University of Cincinnati
“The climate changed rapidly and profoundly. And coinciding with this very rapid global climate change was mass extinctions.” - Kenneth Tankersley
In this video from the University of Cincinnati, Professors Lewis Owens and Ken Tankersley explore a different cave system.In the Great Salt Peter Caves they are attempting to determine the exact age of the cave system.
Astrobiology Magazine contacted Kenneth Tankersley with some additional questions about his research:
Astrobiology Magazine: Has a potential impact location associated with the Younger Dryas Boundary strewnfield been identified?
Tankersley: To my knowledge, the exact impact location has not been identified. It is interesting to note that the Younger Dryas was primarily a northern hemisphere phenomenon, which is the same area where we have identified carbon spherules.
Sheriden Cave is located in Wyandot County, in northern Ohio. Given the presence of nanodiamonds, londsdaleite, and carbon spherules, it suggests a northern impact site.
AM: When identifying spherules, how do you separate strewn-fields that have occurred throughout history? For instance, how do you know a spherule is associated with the YDB strewnfield and not the Chesapeake Bay Impact strewn field?
Tankersley:Sites such as Sheriden Cave are crucial because of the tight stratigraphic and chronometric controls, which are key to pinpointing the age of the strewnfield.
Humans were around at the time of the Younger Dryas, and the changing climate caused by the impact event would have had a profound effect on them as well. The humans of 13,000 years ago were hunter gatherers. As mass extinction occurred around them, they would have been forced to adapt to the corresponding changes in their food sources. The researchers believe that this example of human survival from history could hold lessons for our future on Earth.
“Whether we want to admit it or not, we’re living right now in a period of very rapid and profound global climate change. We’re also living in a time of mass extinction,” Tankersley says. “So I would argue that a lot of the lessons for surviving climate change are actually in the past.”
An image of the X-ray diffraction pattern of lonsdaleite, or hexagonal diamond, from Sheriden Cave. Credit: University of Cincinnati
Why is this research important to Astrobiology?
Studying the effects of impact events on the ancient biosphere of Earth can help astrobiologists understand how similar events in the future could affect the habitability of our planet. Understanding the "principles that will shape the future of life, both on Earth and beyond" is one of the primary goals defined by the NASA Astrobiology Roadmap. Another goal of the Astrobiology Program is to determine how "past life on Earth interacted with its changing planetary and Solar System environment."
“Imagine an explosion that happened today that went across four continents. The human species would go on. But it would be different. It would be a game changer.”