My name is Caleb, I'm 10 years old
and my question is
how do you think dinosaurs became
extinct?
I'm Dr. Dave Lovelace, I'm the research
scientist at the
University of Wisconsin's 
Geology Museum.
Really the prevalent idea currently,
the working hypothesis that
everybody's kind of dealing with,
is what we call the bolide impact.
We have a meteorite that came to the
surface of the Earth,
hit the Earth, and that is what
probably led to the extinction of
the dinosaurs.
We're talking a 10km plus wide chunk
of rock falling from space at
tens of thousands of miles per hour
as it enters our atmosphere.
So this is a huge rock, traveling
really fast
and when it hits the Earth, it creates
an immense amount of destruction.
The crater itself has been found in
the Yucatan peninsula of Mexico.
It's off in the Gulf of Mexico, so the
crater itself is covered by water.
It has been relatively hard to see
until scientists in the 70s
thought this might actually be a crater.
They went in and tested it and, sure
enough, this was definitely
a big crater.
And it looked like the timing would
have been right
for it to be around the time of the
extinction of dinosaurs.
The boundary between the end of the
Cretaceous and beginning of the
Paleogene, the K-Pg boundary, is where 
the dinosaurs go extinct
and on the other side, in the Paleogene,
there are no dinosaurs.
Now what are the immediate impacts?
This gets to be kind of a fun
physics experiment to really understand
when you have a rock this fast coming
through the atmosphere of the Earth,
effectively creating a void, the vacuum
of space following behind it
because it doesn't have time to collapse 
in on itself.
It's traveling so fast, when it hits the
Earth it basically has this
heat in front of it.
The heat of that impact would have created
instantaneous fires
across southern parts of North America,
South America.
It would have had huge devastating
effect locally.
We have the heat coming off, the fires
that are starting,
the material covering the globe,
potentially cutting off light,
which kills off plant life for at
least a little while.
But those are the primary producers
on any ecological scale.
Those are the organisms that are feeding 
everything else.
So if the plants die, the plant-eaters
have no food, they die.
And then the meat-eaters, the 
apex predators,
no longer have a food source, and then
they die.
