Two billion years ago, an impactor hurled towards Earth and crashed into it in an area near Johannesburg, South Africa. It is believed that the impactor was an asteroid and formed what is now the largest crater on Earth. Based on research done previously, scientists have come to the consensus that the Vredefort impact structure was created by an object measuring approximately 15 kilometers (9.3 miles) in size and traveling at a speed of 15 kilometers per hour.
New research by the University of Rochester suggests that the impactor could have been even larger and had catastrophic consequences for the entire planet. The Journal of Geophysical Research published this research and it will enable researchers to better simulate large-scale impacts on Earth and other planets in the future.
Natalie Allen ’20, a John Hopkins University PhD student, says that understanding the greatest impact structure we have on Earth is crucial. Based on her research as an undergraduate at Rochester, Allen was the first to publish the paper. She worked with Miki Nakajima (assistant professor in Earth and environmental sciences), who conducted the research. “Having access the information provided by a structure such as the Vredefort Crater is a great opportunity for us to test our model, and to improve our understanding of the geologic evidence in order to better understand the impacts on Earth.”
Latest simulations suggest a ‘devastating” outcome
The Vredefort Crater has been eroded over the past two billion years. Scientists are unable to accurately estimate the size of Vredefort crater at the time it was formed by the original impact and, therefore, the velocity and size of the impactor responsible for creating the crater.
A 15-kilometer-tall object traveling at 15 km/s would create a crater measuring 172 kilometers in circumference. This is smaller than the current Vredefort crater estimates. Based on new geological evidence, measurements, and current estimates, these current estimates estimate that the structure’s original size would have been between 250-280 kilometers (approximately 150 to 174 miles) at the time of impact.
Allen, Nakajima and their colleagues performed simulations to determine the new size of the crater. The simulations showed that an impactor of this size would need to travel at speeds of 15 to 20 kilometers per hour to create a crater measuring 250 km in area.
The impactor that created the Vredefort-crater would have been more powerful than the asteroid that destroyed the dinosaurs 66 millions years ago and formed the Chicxulub-crater. This impact caused global damage, such as greenhouse heating, widespread forest fires and acid rain. It also caused the Cretaceous–Paleogene extinction that resulted in the death of the dinosaurs.
The Vredefort impact could have had even greater global consequences if the Vredefort volcano was larger and its impact more powerful than the one that formed the Chicxulub.
Nakajima states that the Vredefort Impact was not as severe as the Chicxulub one. This is because there were no single-cell lifeforms at the time and no trees two billion years ago. The impact could have had a greater impact on the global climate than the Chicxulub one.
She says that dust and aerosols from Vredefort’s impact could have spread throughout the Earth and blocked sunlight, cooling down the Earth’s surface. This could have had a catastrophic effect on photosynthetic plants. After dust and aerosols had settled, which could have taken up to a decade, greenhouse gases like cardon dioxide would have emitted from impact. This would have potentially raised global temperatures by several degrees over a prolonged period.
Multi-faceted model of Vredefort’s crater
Researchers were also able to simulate the impact of the material and the distance it traveled from the crater. This information can be used to locate the geographical locations of land masses that existed billions of years ago. Research has shown that material from an impactor was ejected to the present-day Karelia in Russia. Allen, Nakajima and their colleagues discovered that the land mass containing Karelia was only 2,000-2,500 km from the South African crater two billion years ago. This is much closer than what the two areas are today.
Allen states that it is extremely difficult to predict the locations of landmasses in the past. The current best simulations map back approximately a billion years. Uncertainties grow bigger the further back one goes. Researchers may be able to use this ejecta map mapping to clarify their models and complete the view of the past.
Undergraduate research leads towards publication
This paper was inspired by a final assignment for the course Planetary Interiors (now Physics of Planetary Interiors), which Allen completed as a junior.
Allen said that the experience of seeing her undergraduate work published in a peer reviewed journal article was very satisfying and helped her to apply for graduate school.
Allen states, “When Professor Nakajima approached my and asked me if we could work together to make it a publishable piece, it was really gratifying” “I had my own research idea and it was compelling enough for another scientist to decide it was worth publishing!”
She says, “This project was a lot outside my normal research comfort zone, but it was a great learning opportunity and would force me into a new direction. As I was preparing to apply for graduate school, it gave me confidence in my research skills.