An impactor hurtled toward Earth about two billion years ago, crashing into the planet not far from where Johannesburg, South Africa is today. The largest crater on Earth was created by the impactor, which was most likely an asteroid. Scientists agree that an object with a diameter of about 15 kilometers (9.3 miles) and a speed of 15 kilometers per second made the Vredefort crater. This is based on research done in the past.
However, new research from the University of Rochester suggests that the impactor may have been much larger and would have had catastrophic effects on the entire planet. This study, which was published in the Journal of Geophysical Research, helps us learn more about the big impact and makes it possible to make more accurate simulations of impacts that have happened on Earth and other planets in the past and will happen in the future.
According to Natalie Allen, a 2020 graduate who is now enrolled in the John Hopkins University PhD program, understanding the largest impact structure we have on Earth is crucial. The study’s first author, Allen, conducted research with assistant professor of Earth and environmental sciences Miki Nakajima while an undergraduate at Rochester. Allen is the author of the paper. A structure like the Vredefort crater gives us a great chance to test our model and see how well we understand the geological evidence it shows. This will help us understand how impacts happen on Earth and other planets.
New simulations predict “devastating” effects.
The Vredefort crater has eroded over a two-billion year period. The size of the crater at the time of the initial impact and, consequently, the size and velocity of the impactor that created the crater are therefore difficult for scientists to directly estimate.
A crater measuring 172 kilometers in diameter would be created by an object that is 15 kilometers in size and moving at a speed of 15 kilometers per second. This is considerably less than the Vredefort crater’s estimated size, though. Based on new geological evidence and measurements, the structure’s original diameter is now thought to have been between 250 and 280 kilometers (about 155 and 174 miles) at the time of the impact.
Simulations were run by Allen, Nakajima, and their colleagues to match the updated crater size. According to their findings, an impactor would need to be much larger, measuring 20 to 25 kilometers in diameter and move at a speed of 15 to 20 kilometers per second in order to account for a crater 250 kilometers in diameter.
This indicates that the asteroid that destroyed the dinosaurs 66 million years ago and left the Chicxulub crater would have been smaller than the impactor that created the Vredefort crater. This impact not only caused the Cretaceous-Paleogene extinction event that killed off the dinosaurs, but it also caused greenhouse warming, widespread forest fires, acid rain, and the destruction of the ozone layer.
If the crater was even bigger and the force of the impact was even stronger than what made the Chicxulub crater, the effects of the Vredefort impact could have been even worse for the whole world.
Given that there were only single-cell lifeforms and no trees two billion years ago, the Vredefort impact did not leave a record of mass extinction or forest fires, in contrast to the Chicxulub impact, claims Nakajima. However, the impact could have had a more significant impact on the world’s climate than the Chicxulub impact.
According to her, the Vredefort impact would have caused a global spread of dust and aerosols that would have obstructed sunlight and cooled the Earth’s surface. “For organisms that use sunlight for photosynthesis, this might have been disastrous. The greenhouse gases, such as carbon dioxide, released from the impact would have raised the global temperature for a very long time, possibly by several degrees, after the dust and aerosols settled, which could take anywhere from hours to a decade. ”
The Vredefort crater model has many features.
Researchers were also able to examine the material ejected by the impact and the distance it traveled from the crater thanks to the simulations. They can use this knowledge to pinpoint where specific land masses were geographically billions of years ago. For instance, earlier studies found that the impactor’s debris was ejected toward modern-day Karelia, Russia. Using their model, Allen, Nakajima, and their colleagues found that the land mass that includes Karelia would have been only 2,000 to 2,500 kilometers away from the crater in South Africa two billion years ago.
Allen asserts that it is extremely challenging to pinpoint the location of landmasses from the distant past. The best simulations available right now go back about a billion years, and the uncertainties increase as you go back further. It may be possible for researchers to test their models and further our understanding of the past by elucidating evidence like this ejecta layer mapping.
Student research results in publications
The inspiration for this essay came from a final exam for Allen’s junior-level Nakajima course, Planetary Interiors (now called Physics of Planetary Interiors).
Allen says that having her undergraduate research published in a journal with peer review was a very rewarding experience that helped her get into graduate school.
As Allen explains, “It was really gratifying and validating when Professor Nakajima approached me and asked if I wanted to work together to turn it into a publishable work.” I had developed my own research idea, and another scientist found it compelling enough to think it was worth publishing! ”
She adds, “Even though this project was far outside of my normal research comfort zone, I figured it would be a great learning opportunity and force me to use my skills in new ways. It greatly increased my confidence in my capacity for research as I got ready to attend graduate school. “
