♫ What in the world, when, why, where?♫
♫ Who's got the answers? ♫
I'm standing next to some mountains that are millions of years old
and the earth is itself four and half billion years old.
How do I even 
wrap my mind around that length of time?
That's a good question
♫ Good question! ♫
How can you imagine 4.5 billion years?
And how does that compare the amount of time
that humans have been around?
A geologist gave us the idea to use a football
field as a metaphor
and that's exactly what we're going to do
At this end zone we've got the present
And at this end zone is the moment our planet formed
Earth's entire history stretches the full
100 yards in between
Every inch is 1.3 million years
Let's start at the beginning and take a walk through earth's entire history
For the first few hundred million years,
the earth was bombarded with rocks from outer space
but now its starting to calm down
and way up here 3.8 billion years ago,
life begins.
We're talking simple life
- single cells floating in a vast ocean
Now these cells are figuring new ways to
get energy - they're evolving to harness the power of the sun
Photosynthesis starts past the 20 yard line
The air here is mostly carbon dioxide and
nitrogen, but right around here little green
cells start making oxygen...
And up here, about 2.3 billion years ago
oxygen starts building up in the atmosphere
We're halfway down the field and we just got
the kind of atmosphere that humans can breathe
For the next billion and a half years its
paradise for single cells of every variety
But as we move down the field,
cells start working together
And by the time we reach the 18 yard line -- right
here -- there's lots of complex critters floating around
It's 800 million years before the present
... and things are about to get really interesting
Here at the 13 yard line, we've got an ozone layer
And here, a sudden explosion of diversity
530 million years ago, animals take their
first few steps on land.
In the ocean, fish appear!
Land plants!
Insects!
Sharks!
Amphibians!
It's been 4 billion years since we started
and here at the five yard line,
we're just starting to see the first mammals and dinosaurs
We see stegosaurus  dinosaurs right here about
176 million years ago
but we don't see the T. rex until about 4 and a half feet from the end zone
about 68 million years ago.
Look - the T-Rex is closer to us in the present
than it is to the stegosaurus way back there!
Woah - and there's a catastrophe at the one
yard line!
66 millions years ago an asteroid - or volcanoes?
- or climate change? or all three?
killed 75% of all species
But life rallies!
This yard is the yard of mammals
We've got armadillos
giant whales
wolves
And here -- a foot away -- the great apes
- our family!
hippos!
mammoths!
L ions!
Lucy! - almost human but not quite
Saber tooth tigers!
Cattle!
Then 200 thousand years ago - this is where
we find humans that look like us
That's just an eight of an inch from the end zone
The width of this lightbulb
This is all of human experience, but everything we call civilization
-- agriculture, cities,
books, science --
these don't appear until we're two hair's
breadth from the end zone ...
the width of this filament
We just want to say thanks to the Morgan State Bears for letting us do all this weird stuff on their football field
And to you we say - send us your questions, we'll answer them every other Tuesday.
