[♪ INTRO] [Jessi] Hey there! Squeaks and
I are here with our friend Dino. And our library just got a new book that
has pictures of all the different kinds of dinosaurs that used to live on Earth. And it tells a little about them, too... [Dino] ...like what they ate! This page says that some dinosaurs like
Stegosaurus and Triceratops ate plants. So I was thinking that they might
have been friends who hit up the salad bar together.
[J] Uh, Dino... [D]...but they definitely weren’t friends with
the meat eaters, like Allosaurus and T. Rex! I bet they had amazing dinosaur races
as they ran to catch the best food. [J] Dino... [D] Yes, Jessi? What do you think? [J] I think… that it’s fun to imagine
what these animals might have done if they’d met. And I also think we need to remember
that Stegosaurus and Triceratops weren’t around at the same time. [D] Wait. Wait, what? [J] I’m sorry, Dino… but the same
is true for Allosaurus and T. rex. These dinosaurs lived in
different times from one another! [D] I don’t get it! They all lived back
in the time of the dinosaurs, right? [J] Yep, you’re right about that! But the
time of the dinosaurs was a very long time. It lasted millions of years! So all
dinosaurs didn’t live at the same time! [Squeaks squeaks] [J] Oooh, good point, Squeaks. We built a pretend time machine
to imagine what it would be like to travel back in time and see
living things from the past. But to see all of these dinosaurs, we
would have to make more than one trip! [D] So… if we took your time machine
back to the time of the dinosaurs, we’d actually have to go
to lots of different times? [J] Exactly! Scientists divide “dinosaur
time” into three parts… called periods. There’s the Triassic period… which
started over 200 million years ago. Some small dinosaurs like Eoraptor lived then. Next came the Jurassic period. Allosaurus and Stegosaurus
were alive during this period. The Jurassic period lasted over 50 million years. It was after that that dinosaurs
like Triceratops and T. rex came along in a time called the Cretaceous period! [Squeaks squeaks] [J] Oh, you’re right, Squeaks, it
can be pretty hard to think about long periods of time like that. But I have an idea we can use to
show how long ago dinosaurs lived. We can use our bodies as a model! We use models to helps us understand or
explain something in the world around us. By using our bodies as a model of "Dinosaur
Time," we can get a better picture of just how long ago those different periods were! It won’t be perfect… but it will be
a way for us to think about things that happened a long time ago! Now… let’s say that the bottom of
your shoes is the bottom of our model, when the very first dinosaurs appeared. That’s the beginning of the Triassic
period, about 245 million years ago. [D] Okay! [J] Stegosaurus and Allosaurus didn’t
show up until the Jurassic period, about 50 million years later. That means that these dinosaurs would
have lived in the time that starts somewhere below your knee and
ends somewhere around your hips. That distance on your body
represents about 56 million years. [D] Then... it was T. rex time! [J] The Cretaceous period was
about 74 million years long. That means if it starts at your hips,
it should end at about your chest. And the time of the dinosaurs
ended about 65 million years ago. So everything from your chest to the top of
your head represents the last 65 million years! [Squeaks squeaks] [J] Oooh, good question, Squeaks. Humans and their ancestors have only
been on Earth for about 6 million years… so in our model, that would be only the
last couple centimeters of your body. Maybe from the top of your forehead up! [D] Wow, so people haven’t been
around for very long at all! [J] No! Life on Earth was around a long
time, even before there were dinosaurs... and I mean a long time. And over that time, the way earth
looked and the plants, animals, and other kinds of life that
lived here changed a lot! Some of these changes happened
very fast, like volcanic eruptions! But others happened very slowly. So slow that we wouldn't have
noticed they were happening, even if people had been around. [Squeaks squeaks] [J] Oooh, great question! Squeaks wants to know how we
know plants and animals lived during different times if no
one was there to see them! [D]I think I know this one! Is it because of fossils? [J] Good job, Dino! We’ve found fossils bones, footprints,
and other things left behind by ancient animals, plants,
and other kinds of life. We use these fossils as clues to try and
figure out how long ago they might have lived. [D]: How? [J]: Well… one way we can tell which
fossils are older and which are newer is by how deeply they’re buried. Think about paper in a recycling bin. The paper that you put into the empty bin
last week is on the very bottom of the can. And it gets buried by the
paper you throw in later. The very top layer of paper in the recycling
bin is the paper you put in there today, this morning, or even a few minutes ago. [D] Oh… I see! So the fossils that are deep in
the ground, like Stegosaurus, are older than the ones closer to the
top of the ground, like the T. rex. [J]: That’s right! T. rex is pretty young. [D]: … in dinosaur years, anyway! [J]: Yes! Now let’s see what else
we can learn about in this new book. Thanks for joining me here on SciShow Kids. If you want to keep learning and
having fun with Squeaks, Dino, me, and all of our other friends, be
sure to hit the subscribe button, and we'll see you next time here at The Fort! Bye! [♪ OUTRO]
