<ul><li>Earth is the third rock from the Sun </li></ul><ul><li>The order from Sun out is Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto (well, Pluto got downgraded last year from a planet to a planetoid). </li></ul><ul><li>There’s an asteroid belt that runs in between Mars and Jupiter </li></ul><ul><li>Generally, the denser elements collected closer to the Sun. That’s why the rocky planets are all on the inside and the gas giants are the outer planets. </li></ul>
Here are the sizes of the planets relative to each other. Did you know that Jupiter has 318 times the mass of Earth and 1,400 times the volume? Or that Jupiter acts as an asteroid catcher?
Here are the sizes of the inner four terrestrial (rocky) planets relative to each other. Mercury Venus Earth Mars
And here are the sizes of the planets relative to the Sun. The Sun is big. That’s you.
We nearly went to 12 planets. The folks who decide what characteristics define a planet (the International Astronomical Union) once proposed that a planet be an object that orbits the Sun (but is not itself a star) and possesses enough gravity to pull itself into a roughly spherical shape. That meant these three could have been planets:
It’s possible this definition could have also qualified another 12 celestial objects as planets: Those elementary school styrofoam models of the solar system could have gotten a lot more complicated.
<ul><li>The Earth has layers </li></ul><ul><li>At the center is the inner core. It has solid iron and nickel. </li></ul><ul><li>Next out is the outer core. Its iron and nickel is in a liquid state. </li></ul><ul><li>Then you have the mantle. </li></ul><ul><li>And then the crust, which is the layer we see here on the surface. </li></ul>
Volcanoes form when magma (molten rock) erupts through the crust from the mantle. We’ll talk about them more in 2.3.
<ul><li>Continental Drift </li></ul><ul><li>Because the continents are on tectonic plates that are essentially floating on molten rock, they move around. </li></ul><ul><li>Once upon a time, over 200 million years ago, all seven continents were part of the same supercontinent, Pangaea, and was surrounded by a superocean, Panthalassa </li></ul><ul><li>We’ll talk more about this in section 3 </li></ul>
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