New research shows how large asteroid impacts may have deformed rocks in a way that created habitats for early life on Earth and elsewhere.
Around 65 million years ago, a massive asteroid crashed into the Gulf of Mexico. The Chicxulub impact was so huge that the blast and its aftermath wiped out about 75 percent of all life on Earth, including most of the dinosaurs.
In April and May, scientists on an offshore expedition drilled deep into part of the Chicxulub impact crater to retrieve samples from its rocky inner ridges—known as the “peak ring”—drilling about 1,600 to 4,380 feet below the modern-day sea floor to learn more about the ancient cataclysmic event.
Findings from the first analysis of the core samples show that the impact deformed the peak ring rocks, making them more porous and less dense than models had predicted. The work appears online in Science
“Chicxulub crater is the only crater on Earth that has such a well-preserved peak ring and since we can’t get samples of peak rings from other planets yet, it’s really our best window into understanding the formation of large impact basins anywhere in the solar system,” says Sonia Tikoo, assistant professor in the earth and planetary sciences department at Rutgers University.
“We really didn’t know the exact physical mechanisms behind how peak ring craters form until this study.”
Porous rocks provide niches for simple organisms to take hold, and nutrients would also be available in the pores from circulating water that would have been heated inside the Earth’s crust. Early Earth was constantly bombarded by asteroids—and this bombardment must have also created other rocks with similar physical properties, researchers say. This may partly explain how life took hold on Earth.
The study also confirmed a model of how peak rings formed in the Chicxulub crater, and how peak rings may be formed in craters on other planetary bodies.
The asteroid that created the Chicxulub crater hit the Earth’s surface with such force that it pushed rocks—at the time about 6 miles beneath the surface—farther downward and then outward, the new study confirmed. These rocks then moved inward toward the impact zone and then up to the surface before collapsing downward and outward again to form the peak ring. All told, the rocks moved about 18.6 miles in a few minutes.
“It is hard to believe that the same forces that destroyed the dinosaurs may have also played a part, much earlier on in Earth’s history, in providing the first refuges for early life on the planet,” says lead author Joanna Morgan, professor of Earth science and engineering at Imperial College London. “We are hoping that further analyses of the core samples will provide more insights into how life can exist in these subterranean environments.”
Tikoo, who studies magnetic fields preserved in rocks, adds “it’s surprising that we have this possible habitat down there in an environment that experienced so much energy and heat and deformation. It’s incredible that a biosphere may be produced in that environment as well.”
Researchers will next make detailed measurements from the recovered core samples to refine their numerical simulations. Ultimately, the team is looking for evidence of modern and ancient life in the peak-ring rocks. They also want to learn more about the first sediments that were deposited on top of the peak ring. That could tell the researchers if a giant tsunami deposited the sediments, and provide insights into how life recovered and when life returned to this sterilized zone after the impact.
Tikoo has studied the physical properties of the rocks and the granite “basement” that makes up the much of the peak ring. That includes preparing and examining the samples, and making density, porosity, and magnetic measurements. “I have about 400 samples in my lab right now and in the coming months, I’m going to start looking in more detail at the magnetization of these rocks,” she says.
“Magnetism can be used to detect minerals created by impact-related hydrothermal systems. You could potentially have hydrothermal systems forming in the Martian crust where you have warm water moving through and we’ve shown that life may be able to exist in those environments here. It’s possible that a similar process could have happened on Mars long ago. It’s another place to look for fossil evidence of life in the past.”
The expedition was conducted by the European Consortium for Ocean Research Drilling (ECORD) as part of the International Ocean Discovery Program (IODP). The expedition is also supported by the International Continental Scientific Drilling Programme (ICDP).
Source: Colin Smith for Imperial College London, Rutgers University