The Asteroid Impact That Evaporated The Oceans

By Debra Kelly on Friday, February 12, 2016
“The skies will rain fire, the oceans will boil, the streets will run red with the blood of billions.” —Darkseid, “Justice League”

In A Nutshell

When scientists started recreating what would have happened to the planet after the impacts of the asteroids that left the giant craters in Australia and South Africa several billion years ago, they found some mind-numbing implications. Off-the-chart earthquakes that lasted for half an hour sent ripples through the Earth’s tectonic plates, the skies burned, vaporized rock fell like rain, and the oceans boiled away. These planet-killers were two to three times the size of the asteroid that killed the dinosaurs, and they created some of the strangest formations on the planet today.

The Whole Bushel

In the 1970s, father-and-son geologist duo Luis and Walter Alvarez were looking at how changes in soil composition corresponded to changes in the fossil record when they stumbled on the answer to a question that had been plaguing the scientific community for ages: What killed the dinosaurs?

The most agreed-upon answer is now pretty well-known: A 10-kilometer-wide (6 mi) asteroid hit the Yucatan Peninsula about 66 million years ago. (The crater is now known as the Chicxulub impact crater.) After the discovery, all the best and brightest minds of the scientific community were trying to piece together what kind of fallout such an impact would have.

They’ve come up with some terrifying guesses, including a massive dust cloud that blocked the sunlight for months and a rain of fiery rocks that came crashing down.

But those effects—along with with extinction of the dinosaurs—have turned out to be peanuts compared to what happened with the impact of an even bigger asteroid a few billion years ago. Vredefort is currently the largest impact crater we’ve found, and it’s 300 kilometers (185 mi) wide. Another crater is buried deep beneath the planet’s surface in Warburton, Australia, and although it doesn’t seem to have a worldwide extinction event associated with it, we can still learn a lot from it.

The study, done by Stanford University and published by the Geochemistry, Geophysics, Geosystems journal, attempted to trace the effects of the impact across the world. The asteroids are estimated to be about four or five times the size of the one that later hit the Yucatan, so they made quite an impact.

The resulting earthquake would have been off the charts. The scientists estimate that a series of tremors would have lasted for more than half an hour at any single location.

The resulting tsunamis would have been several kilometers in height, and the entire surface of the planet would have been re-shaped, especially when the other asteroids started hitting. Craters in South Africa have helped support the theory that dozens of impacts happened between three and four billion years ago, battering the planet in what’s been appropriately called the Late Heavy Bombardment period.

The asteroid apparently responsible for killing the dinosaurs put off more than a billion times more energy than the atom bombs that hit Japan during World War II, and multiplying that for these larger impacts suggests that not only did the temperature of the planet skyrocket, but the top layers of the oceans would have boiled away. Rocks were vaporized and thrown into the air. Once they cooled, they would have fallen like rain.

Scientists think these impacts may have been responsible for geologic phenomena like the Barberton greenstone belt, an area along the border of Swaziland that is made of some of the oldest rocks on the planet.

These rocks shouldn’t be at the surface without a catastrophic event big enough to send ripples through the tectonic plates.

While these impacts didn’t have the effect on life that the Chicxulub impact did, some have suggested that if that asteroid hadn’t hit exactly when it did, the dinosaurs might have survived and humans might not have made their rise to the top of the food chain.

According to an Edinburgh University paleontologist, the impact happened near a weakening in the diversity of the dinosaur species due to temperature changes and a loss of lower-level food chain animals. Give or take a few million years for the asteroid, and today’s planet might would look extremely different.

Show Me The Proof

Nature: Hints of huge buried impact craters reported in Australia
Stanford University: Scientists reconstruct ancient impact that dwarfs dinosaur-extinction blast
The Guardian: Asteroid’s ‘bad timing’ killed off dinosaurs, new evidence shows
Planetary Science Institute: The Impact That Wiped Out the Dinosaurs