I'm Fraser Cain, the publisher of Universe
Today.
Dinosaurs roamed the Earth for 135 million
years.
Filling every ecological niche, from the oceans,
forests and plains; even the skies.
Then, 66 million years ago, something terrible
happened.
In a geological instant, 75% of the plants
and animals on Earth went extinct.
.... And all of the land dinosaurs were wiped
off the Earth forever.
What happened?
What killed them off?
What could have caused that much damage in
such a short amount of time?
The key to this mystery was found in a strange
layer of ash sandwiched between layers of
rock deposited 66 million years ago.
This line, known as the Cretaceous--Paleogene
boundary, is found across the world in the
geologic record and it marks the moment when
everything DIED.
What's interesting about this layer is that
it's rich in iridium, a rare element on Earth,
but abundant in asteroids.
And so, geologists found the most likely culprit:
an asteroid.
This evidence matched the discovery of an
enormous asteroid impact basin in the Yucatán
Peninsula in Mexico, centered near the town
of Chicxulub.
The rock debris in this area could be dated
back to approximately 66 million years old,
matching the worldwide layer of ash.
We now know that an asteroid at least ten
kilometres across slammed off the coast of
Mexico 66 million years ago, releasing 2 million
times more energy than the most powerful nuclear
bomb ever detonated.
The effect of this impact is mindblowing.
Millions of tonnes of rock were ejected into
space on ballistic trajectories.
Reheated by atmospheric re-entry, this debris
superheated the air across the entire planet,
catching the world's forests on fire.
Shockwaves radiated outward from the impact
site, inducing earthquakes and volcanoes along
their path.
Mega tsunamis thousands of meters high spread
out from the impact site, pounding coastlines
around the world.
Dust rained down across the planet.
It filled the air, darkening the skies for
decades, and preventing photosynthesis.
Plants on land and in the oceans were unable
to produce energy.
The planet cooled from the choking dust and
aerosols, followed by years of acid rain,
and then even global warming as the carbon
from the blasted life filled the atmosphere.
The effects to life were devastating.
It's no surprise the land dinosaurs didn't
make it through this impact event.
In fact, it's a bigger surprise that our ancient
ancestors, hardy early mammals could endure.
And our final sobering thought is that impacts
of this scale have happened many times in
the past, and will happen again in the future.
It's not a question of if, it's a matter of
when.
Thanks 
for watching!
