If the Earth Has Been Hit By Hundreds of Meteors, Then Where Are The Craters?

The Most Distinctive Thing About the Moon Are The Craters That Cover It.

The far side of the moon

Because of the quirk of physics that mean that the moon is tidally locked with the Earth, we have had hundreds of thousands of years to ponder its face. Many western cultures see this as a man or woman on the moon, and many eastern cultures view it as a woman, rabbit or toad on the moon: but whatever it might appear, it is so distinctive because of its craters. Look to the far-side of the moon and, while more unfamiliar in appearance, you can't help but be amazed by just how pockmarked the surface really is.

We know that the moon's lack of atmosphere is part of the reason why the craters are so easy to see, and surely it can't have blocked every asteroid* that came across Earth's path. After all, it's thought that a huge meteorite* was what caused the climate change that wiped out the dinosaurs. But if the Earth was hit by a lot of asteroids in its path, where the heck are the craters?

Well, billions of years of erosion may have hidden them, but they are most certainly still there if you look hard enough. Here are 5 of the most interesting craters on Earth.

Photo by D.Roddy and L.P.I

Preserved and Perturbing: The Barringer Crater in Arizona

At 49,000 years old, just under a mile across and still startlingly visible, the Barringer meteor crater is certainly a sobering sight.
The explosion was the equivalent of 2 and a half million tons of TNT, resulting from the huge crater travelling at 26,000 miles per hour before impact. Most of the meteorite itself was metal and would have melted on impact to practical atomisation, as well as sending huge dust clouds of rock out to scatter the cooler and wetter landscape of Arizona that existed in the ice age. A lake formed in the bottom of 750 foot deep crater before, as the ice age ended and things heated up, it eventually dried up. The desert itself limited any erosion, which is why the crater is so obvious today, but it wasn't until 1891 that the site was scientifically designated as an impact crater.

Photo by NASA

Diamonds are Forever: The Popigai Crater in Russia

35 million years ago, in what is now the Tamyr Peninsula of northern Siberia, a metor between 3-4 miles wide smashed into the Earth at a speed of over 44,000 miles per hour, creating a crater 62 miles wide impact crater with a rim of deformed rock that is 12 miles wide. The sheer force of the impact vaporised rock and created incredible heat and pressure that was enough to form diamond deposits some 7 miles from the point of impact underground.

It is unlikely that these diamonds will be mined in the near future, as nowadays we are able to make our own synthetic diamonds for industrial use, and the Siberian climate is very unforgiving. While what was created are diamonds in name, they may just not be useful enough to us to put in the effort to mine. That said, in addition to the diamonds there is thought to also be lonsdaleite. This hexagonal carbon material is very rare and some specimens are thought to potentially be even more durable than diamonds. The characteristics of these specimens haven't yet been verified in the Popigai crater, but should we ever need them it may be worth a look in the future.


The Dinosaur Killer: The Chicxulub Crater of Mexico

Credit: LPI

It can be easily argued that perhaps the most important impact crater on our list is that of Chicxulub in Mexico because it thought to have led to the most famous mass extinction in prehistory - the eradication of the dinosaurs. This crater is more that 110 miles wide, belonging to a meteor that was likely to have been 6 miles in diameter itself. When it struck the Earth it would have released as much energy as a billion 'Big Boy' nuclear bombs (or 100 trillion tons of TNT). While this may not have been the only contributing factor to the dinosaurs extinction, it certainly dealt a crippling blow. Much like the clouds of ash that follow a huge volcano's eruption, the impact would have badly damaged the delicate balance of the climate for the surviving creatures.
Chicxulub isn't clearly visible from the surface, but can be determined by analysing a distinctly spacey layer of material in the soil.


The Big Daddy: The Vredefort Crater of South Africa

While the chicxulub crater certainly had a devastating effect (that doubtless worked in our favour for us mammals) it was by no means the biggest to hit Earth. That honour belongs to the Vredefort crater in South Africa. Luckily, at 2.02 billion years old, there wasn't a lot of life for it to devastate: we only started shuffling about on land 375-359 million years ago. Which is lucky, as the meteorite itself would have been larger than South Africa's Table Mountain. It created a impact crater that was originally 185 miles across. Wowza.

Erosion has hidden much of the crater over time, but it is particularly interesting as it is a crater with multiple rings, just like the Valhalla Crater on Jupiter.

The Great-Granddaddy of all Earth's Craters: Maniitsoq in West Greenland

Recently identified as possibly the world's oldest meteorite crater, Maniitsoq in Greenland is home to a huge impact zone that is 62 miles wide, which assumes that it was created by a meteor that was at least 19 miles wide.

Location of the ancient crater (Credit; GEUS)

This is thought to be 3 billion years old and so, as you can imagine, is difficult to spot. It was discovered not on the field but rather in an office when the scientist Adam Garde noticed that there was an unusually high level of nickel and plutonium in one region of West Greenland. High levels of rare and valuable materials like this so often come from space when in concentrated amounts, so he was suspicious. Sure enough, this matched with the odd geological features of the region pointed to a hidden but very ancient impact crater. With little atmosphere at the time, Earth didn't stand a chance.






* Note: Technically, according to the Universe Today definitions, if space rock hits Earth it's called a meteorite. Asteroids are those that zoom around between Mars and Jupiter and shoot off towards earth. Comets are ice and rock shooting through space with long tails, and meteors are meteorites that haven't hit earth yet and often burn up. I'm no scientist, ladies and gents, so please excuse me if I use the wrong term, I'll do what i can to use the right terminology.


Sources
-Why is the moon so scarred with craters?
-Tidal Locking
-Lunar Paridoleia
-Far side of the moon
-'Crash!' 10 biggest impact Craters on Earth
-World's oldest meteorite crater on Earth found
-Universe today; what's the difference between a comet, asteroid and meteor?
-Asteroid impact that killed the dinosaurs: New evidence
-Barringer meteor crater
-World's oldest meteorite
-Diamonds beneath the Popigai crater

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