Two billion years ago, the Vredefort impactor struck Earth, creating the planet's largest impact structure. Turns out we underestimated it.
“Understanding the largest impact structure that we have on Earth is critical.”The Vredefort impactor struck Earth about 2 billion years ago during theand is now located in South Africa. Previous research put the Vredefort impactor at between 10 to 15 km in diameter, and the crater — or impact structure as scientists call them — was about 160–300 km across when it was formed.
More recent impacts like the Chicxulub event also had far-reaching and catastrophic consequences. Chicxulub caused megatsunamis, violent earthquakes, firestorms that turned forests to ash and cinders, atmospheric dust accumulations that caused global temperatures to drop for a sustained period of time, and of course, the extinction of the dinosaurs. But Earth was much different when the Vredefort impact event occurred in the Paleoproterozoic Era. There were no animals and no forests.
The size of the crater isn’t the only evidence that lines up with the impactor’s revised diameter and velocity. Certain features in the rock under the impact site also suggest a larger impactor than thought. Researchers have found shock-metamorphic features in the Vredefort impact structure, including “… breccia, shatter cones, planar deformation features in quartz and zircon, and melt,” the authors write. Their location suggests that the impact was more powerful than thought.
The impact thickened the atmosphere with dust and aerosols, blocking out sunlight and causing temperatures to drop. At the time, oxygen was accumulating in the atmosphere, and photosynthetic organisms were widespread and had been around for a billion years already. What happened to them? The authors refrain from an exact explanation of the consequences for life on Earth at the time. But they do arrive at several conclusions.
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