Science & Technology

An Australian Crater Could Force Us to Rethink How We Judge a Planet's Age

A rock the size of a semitrailer that smacked Australia more than 100,000 years ago could help us better understand the universe. Astronomers just recalculated the age of an ancient desert crater and discovered that it's much younger than previously thought. By studying craters on Earth, we can better estimate how often comets and meteorites smacked into worlds around our solar system, thereby calculating their ages — and based on this work, we may have to rethink everything we know.

Younger Than It Looks

The scar of that ancient collision in Australia is called Wolfe Creek Crater, and it's rather large, having been formed by a meteorite that was likely 50 feet (15 meters) in diameter. The object slammed into the desert and created a divot that's been deemed the second largest crater on Earth from which fragments of the meteorite were recovered. Craters often disappear underwater or via geologic activity, so we're lucky to have this find available to us.

Scientists initially pegged the crater as 300,000 years old, putting it at about the same age as the human species. But the new estimate suggests it's actually quite a bit younger, at only 120,000 years old, dating back to a warmer period on Earth known as the Eemian interglacial period. (On a side note, the Eemian is interesting to scientists studying climate change today, as some studies suggest our Earth nowadays is as warm as it was way back then.)

How did this new age estimate arise? It was probably in part due to the fact that we have better scientific equipment than we did before. Also, researchers used two independent dating techniques: exposure dating, which estimates how long the sediment has been exposed to cosmic rays on the Earth's surface, and optically stimulated luminescence, which measures how long ago sediment — in this case, sand buried after the impact — was last exposed to sunlight.

"Results from the two dating techniques mutually support each other within the same age range," said lead author Tim Barrows in a statement.

Counting Craters

Re-dating the crater in Australia has implications that could rock our solar system. There are planets and moons and tiny worlds with rocky surfaces all over our planetary neighborhood, some of the more famous being Mercury, the Moon, and Pluto. Astronomers estimate the age of their surfaces by using a technique called crater counting, which is exactly what it sounds like: They count the number of craters in an area and compare that number with an estimate of how often a small world smacks into the surface.

Simply put, if scientists find a crater that's younger than expected, that might mean that the rate of objects hitting Earth (and other worlds) slightly increases. With this new measurement, the research team estimates that large objects smack into our planet about once every 180 years or so. In roughly the last century, we know of two such events: an object that flattened 800 square miles (2,000 square kilometers) of forest in Tunguska, Siberia in 1908, and another that shattered glass and injured people when it broke up over the Russian town Chelyabinsk in 2013.

NASA is, of course, on the case with a fleet of telescopes scanning the sky for any possible threats to Earth. Fortunately, they've found nothing pressing that could flatten a city, although they continue the search just in case — and they're also aware that smaller objects (like Chelyabinsk) can still sneak through since they're below the detection threshold of some telescopes. However, don't lose any sleep yet. The agency will let us know if they find something worrying.

In the meantime, the larger implication to take from this study is that the ages of craters all over the solar system may have to be reconsidered. The famous Meteor Crater in Arizona, for example, got a similar treatment from these researchers. They calculated that it's likely to be 61,000 years old, which is about 10,000 years younger than previously estimated. So it will be interesting to see how this changes our understanding of ancient climates and life on our own planet — and on other worlds.

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Learn more about the rocks that hit our planet in "Fire in the Sky: Cosmic Collisions, Killer Asteroids, and the Race to Defend Earth" by Gordon L. Dillow. The audiobook is free with an Audible trial. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Elizabeth Howell December 20, 2019

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