>>AKI WATANABE (paleontologist, NYIT & AMNH):
Did an asteroid kill the dinosaurs?
[MUSIC] [BOOM]
>>WATANABE: Paleontologists agree that an
asteroid did strike Earth at the end of the
Cretaceous period, at around 66 million years ago.
And we know this because there is an impact
crater in the Yucatan Peninsula of
what's now Mexico.
And the rock layers from that age include
an element called iridium which is rare on
Earth but relatively abundant on asteroids.
And you can learn more about the asteroid
itself by clicking the link here.
It obviously had a drastic impact on life
forms on Earth, including dinosaurs like
T. rex and Triceratops.
So because the asteroid was really big, the
impact would have had global consequences,
both immediate and then also long-term.
There would have been initial effects like
forest fires and giant tsunamis, but the projectiles
that came off of the impact would have led
to impact winters, which would have cooled
down the Earth and also blocked sunlight from
hitting the ground.
And the vegetation would have suffered, which
would have led to the collapse of a lot of ecosystems.
So its very clear that the asteroid impact
had a major effect on life on Earth.
But what we’re trying to figure out is whether
the asteroid was the only factor, or the major
factor that led to the extinction of dinosaurs.
Some palentologists have proposed that the
dinosaurs were already on a decline before
the impact of the asteroid.
But this hypothesis is difficult to prove
just because we don’t have a clean complete
record of dinosaurs right before, during,
and after the extinction event.
So it’s hard to tell whether all the dinosaurs
were already on a path to extinction, even
without help from the asteroid impact.
There’s also evidence of an increase in
volcanic activity at that time.
There was a lot of lava and volcanic particles
spewing out from under ground.
This would have led to similar effects as
the impact winters.
So the increase in volcanism might have contributed
additional forces that led to
the extinction of dinosaurs.
It’s not all doom and gloom though.
One dinosaur group we know as birds did survive
through the extinction event.
And also us mammals did as well.
What the fossil record tells us is that certain
animals, usually smaller-bodied and also those
that lived in the oceans tended to fare better
at this extinction event.
So all the animals that are alive today represent
descendants from a group that actually did
survive this asteroid impact.
So to answer the original question, the 
asteroid impact did have a devastating
effect on the dinosaurs.
But paleontologists are still working out
the finer details.
And learning more about this extinction event,
could help us to learn about other extinction
events, including the one we’re 
facing right now.
Thanks for watching the video.
To learn more about the asteroid, make sure
to click the link above for
this weeks' space video.
And if you have any questions about dinosaurs,
leave them in the comments section below.
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