What you are looking at is a satellite view of not one, but two adjacent impact craters
in the tundra of northeast Canada.
Known as the Clearwater Craters, these two impact craters were once thought to have originated
from a single impact event where a large asteroid fragmented in two before before entering the
atmosphere.
After all, we witnessed this exact scenario occur in 1994 where a large comet called shoemaker
levy broke into a dozen pieces before impacting Jupiter.
However, recent evidence has shown that despite the odds, the proximity of these two craters
within Canada truly is just a coincidence.
They formed from separate impact events 180 million years apart.
This video will discuss when exactly these craters formed, what the landscape was like
at the time, and the consequences the asteroid strikes had on the planet.
The Clearwater Craters can be found a remote northern section of Quebec.
Specifically, it is 130 kilometers east of the edge of Hudson Bay.
The two Clearwater Craters are divided by their relative location and are thus named
Clearwater West and Clearwater East.
The larger of the two is Clearwater West which measures 36 kilometers or 22 miles wide.
Meanwhile, the smaller Clearwater East crater measures 26 kilometers or 16 miles wide.
So, how do we know that these massive craters were not formed from the same impact?
The answer is radioactive argon dating.
By heating rock and releasing two isotopes of argon, you can determine the approximate
age of a rock.
In this case, the relative abundances of these isotopes showed that Clearwater West is 286
million years old, while Clearwater East is much older at 460 million years old.
Approximately 460 million years ago, a large asteroid was on a collision course with earth.
This asteroid measured 2300 meters wide.
Known as a type CL carbonaceous chondrite, this asteroid was a member of the first group
of asteroids to form during the beginning of the solar system 4.57 billion years ago.
As it approached Earth, this mass of rock was traveling at 18 kilometers per second
or 40,000 miles per hour.
Entering the atmosphere, a bright streak of light would have been visible across a wide
swath of the planet.
Only a few seconds later, this asteroid struck off the coast of a continent in a shallow
sea during the middle Ordovician period, when numerous trilobites roamed the ocean.
This created a massive explosion equivalent in energy to the detonation of 542 billion
tons of tnt.
In mere moments, anything within a 450 kilometer radius ignited due to the immense thermal
radiation.
Further away, at a distance of 700 kilometers, any plants would have been knocked over as
they faced a 155 kilometer per hour wind from the shockwave.
Due to the size of this impact, large fragments of ejected rock fell across the planet starting
numerous wildfires.
As the dust cleared, a large impact crater measuring 26 kilometers across became visible.
Despite the energy released by this impact, and the subsequent impact winter, it did not
cause any mass extinctions.
Many millions of years later, approximately 286 million years ago, a slightly larger asteroid
was on a collision course with earth.
This asteroid measured 2800 meters wide, and was far more dense than its prior counterpart.
Traveling at a similar speed of 18 kilometers per second, it impacted the ground a mere
30 kilometers to the northwest of the adjacent Clearwater East Crater.
At this period of Earth's history, the impact site was a humid Permian rainforest in the
center of the supercontinent Pangaea.
Impacting with the equivalent energy of 1.4 trillion tons of tnt, it devastated the landscape
in a several hundred kilometer radius.
Owing to its larger size, a 36 kilometer wide impact crater formed.
In the thousands of years following this impact, the underlying crust at the deepest part of
the impact crater began pushing upwards.
A good analogy is removing the top third of a sponge in water.
It will still float, and the removal of this section will cause it to rebound upwards.
Thus, the center of the impact crater was uplifted by more than 1000 meters, forming
a domed center.
In the many millions of years since, the top of the dome eroded away, leaving behind a
ring structure of islands.
I hope that you enjoyed this video!
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