JOAN CARTAN-HANSEN, HOST: The Earth is our home, but it's made up of many complex systems working together to keep us alive.

Find out more about the Earth.

Stay tuned, Science Trek is next!

[MUSIC] STUDENT 1: Let's see who can keep it up in the air for the longest.

STUDENT 2: Okay.

STUDENT 1: Did you know the Earth is 93 million miles from the sun?

CARTAN-HANSEN: The Earth is the third planet from the sun.

The earth's orbit is more like an ellipse rather than a perfect circle.

The Earth spins on an axis, an imaginary line that goes from pole to pole.

The Earth floats at a tilt, and it's that tilt that gives us our seasons as the earth travels around the Sun.

When the northern hemisphere tilts away from the sun, we have winter.

And as the northern hemisphere tilts towards the sun, we get summer.

And because the Earth is spinning on its axis, one side of the planet faces the sun and the other is in the shadow.

That's what gives us day and night.

STUDENT 2: So did you know that oxygen only makes up about 20% of our air?

CARTAN-HANSEN: The earth is covered by a blanket of gases known as the atmosphere.

The troposphere is the lowest level.

That's where you will find the air we breathe.

The air is about 20% oxygen and about 70% nitrogen.

And the rest is made up of other gases.

All of the earth's weather happens in the troposphere.

The next layer is the stratosphere.

This layer contains ozone, a gas that protects us from the harmful ultraviolet rays of the Sun.

After that, is the mesosphere.

This is the layer where meteorites from space usually burn up creating shooting stars.

Then there is the thermosphere, and finally the exosphere.

This is the outermost layer at the edge of space.

STUDENT 3: Let me play!

Let me play!

STUDENT 2:No way.

You're turn.

STUDENT 1: So did you know that the Earth's crust is always moving?

CARTAN-HANSEN: The Earth has four main Layers.

At the center is an extremely hot metal core.

The core is made up of two regions.

The inner core is made up of solid iron and nickel.

Scienctists think the outer core is made up of liquid iron.

They think that the circulation of that liquid causes the magnetic field around the earth.

The Earth's next layer is the mantle, and then the outer layer layer, the layer we live on, is known as the crust.

The crust is about four to 40 miles thick, and makes up less than 1% of the Earth's mass.

It is broken up into pieces known as tectonic plates.

Tectonic plates are pushed and pulled around by the slow and steady movement of the underlying rock.

As the plates move, stresses build up.

Earthquakes happen when these stresses grow big enough that the plates slide past one another quickly, and we feel that shaking.

Most volcanoes also appear along plate boundaries.

Lots of things can change the Earth's surface.

Some change happens quickly from strong forces like earthquakes and volcanoes.

Others happen over great periods of time because of processes like erosion from wind or water.

You can see patterns in rock formations and fossils in rock layers that show changes in the Earth's surface over time.

Humans change the look of the Earth's surface, too.

Buildings, farms, mines are just a few ways that we have changed the look of the earth.

STUDENT 1: And did you know that most of the Earth's surface is covered with water?

CARTAN-HANSEN: 70% of the earth's surface is covered by oceans.

Only .

008% of the earth's fresh water is found in lakes, rivers, and streams.

And that's the water that we need to Live.

So, when you think about the Earth, think about the systems That make up the planet.

The geosphere, the soil, sediments and solid and molten rock.

The hydrosphere, the water on Earth.

The atmosphere, the levels of air and gases around the earth.

And the biosphere, all the Eco-systems and living things on Earth.

STUDENT 1: That's a lot to think about.

STUDENT 3: Please let me play!

STUDENT 2: Go get your own ball.

STUDENT 3: Okay.

If you're going to play with one that looks like the earth, I am going to play with one that Looks like the sun.

STUDENT 1: What was that all about?

Oh my gosh.

STUDENT 2: Run!

CARTAN-HANSEN: If you want to learn more about the Earth, check out the Science Trek website.

You'll find it at ScienceTrek dot org.

[MUSIC] ANNOUNCER: Presentation of Science Trek on Idaho Public Television is made possible through the generous support of the Laura Moore Cunningham Foundation, committed to fulfilling the Moore and Bettis family legacy of building the great state of Idaho.

By the Idaho National Laboratory, mentoring talent and finding solutions for energy and security challenges.

By the Friends of Idaho Public Television and by the Corporation for Public Broadcasting.