Approximately 67 million years ago, the plant and animal life around Earth looked completely
alien.
Across much of the dense rainforests and deserts, towering bird like reptiles known as dinosaurs
were the dominant lifeforms.
So, why are reptiles no longer the dominant lifeforms on the planet today?
The answer is one of the planet's deadliest mass extinction events which was caused by
the largest confirmed impact event in the last 1 billion years of the planet.
The impact crater in question which was left by this catastrophic event can be found off
of the Yucatan Peninsula, being known as Chicxulub Crater and measuring 180 kilometers or 112
miles wide.
Yet, despite the mountain of evidence, the story of the Cretaceous Paleogene mass extinction
event might not be complete.
This is because there is now some evidence that the impacting asteroid which would go
on to strike the planet in what is now modern day Mexico may have had an orbiting neighbor
which separated before the collision occurred.
In other words, the impacting body might have been a binary asteroid.
As a result, the same event may not have resulted in just one but two separate impact craters.
This second and lesser known potential crater is now located a vast distance to the east
southeast of Chicxulub Crater, at a distance of 4,862 miles or 7,825 kilometers.
There, 320 kilometers south-southwest of the capital city of the nation of Guinea Bissau,
it a submarine impact crater.
Although the exact dimensions of this crater are not entirely clear, a paper I am referencing
which is being attributed on screen suggests the crater has a diameter of at least 8.5
kilometers.
This crater being known as Nadir Crater is presumed to have a complex structure with
a central peak which is somewhat visible by overlaying Google Earth elevation data of
the seafloor. 66 million years ago, a large 17.5 kilometer
wide asteroid was on a collision course with Earth which was being orbited at a fairly
close distance in astronomical terms by a smaller 755 meter or 2,477 foot wide asteroid.
As these asteroids approached the planet, they were travelling at a speed of 17 kilometers
per second or 38,000 miles per hour.
These two asteroids eventually separated and entered Earth's upper atmosphere.
The smaller asteroid would go on to impact a spot in the ocean which was at least 800
meters deep.
This generated a powerful explosion equivalent in energy to the detonation of 26,800 million
tons of TNT.
As a deep crater was created, a powerful shockwave raced outwards in all directions which at
a distance of 5 kilometers from the impact site generated a 11,400 mile per hour wind.
While the equivalent to a magnitude 7.2 earthquake was generated, large volumes of displaced
and uplifted water created a towering megatsunami which at a distance of 15 kilometers from
the impact site had a height of 762 meters or 2,500 feet.
This tsunami would then go on to crash into the coastline of the African continent, where
land at a distance of 210 kilometers away from the impact site encountered a 50 meter
high tsunami which would arrive 38 minutes after impact.
While this impact in of itself had severe effects, it only produced a mere fraction
of the mass extinction level larger impact 5500 kilometers away which may have produced
an energy equivalent to the detonation of as much as 300 million megatons of TNT.
Together, these impacts created a global impact winter which would cause the extinction of
the non avian dinosaurs.
Of course, it is possible that the recently discovered Nadir Crater formed a few tens
or hundreds of thousands of years before or after the Chicxulub Crater impact.
After all, on average an asteroid impact on Earth involving a Nadir Crater sized asteroid
which the referenced paper suggested instead had a diameter of only 400 meters across occurs
about once every 100,000 to 700,000 years.
Thanks for watching!
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Additionally, I would like to thank Susan L for becoming a channel member on youtube
of GeologyHub!