Earth Science Lesson 1
The Solar System

Pre-Test
Q&A	The Moon and Beyond

Instruction 1-1

The Solar Nebula/Earth's Formation from the Nebula | Cloud of Dust Theory | Formation and Origin of the Moon | Early Earth | The Sun | Effects of Asteroid Impacts in Shaping the Surface of Planets | Evidence for the Existence of Planets Orbiting Other Stars | Summary

The Solar Nebula/Earth's Formation from the Nebula
http://www.nineplanets.org/origin.html

How did the Earth come into existence? We have all thought of this question. Many explanations have been offered. Every time we make discoveries, the scientific theories are adjusted. There are movies and TV shows about it. But although they are entertaining, they can be unscientific.

Here are the latest scientific theories.

When the universe began, about 15 billion years ago, there was no Earth or Solar System. All there was were two gasses: hydrogen and helium.

That’s right, everything in the universe began with just two gasses: hydrogen and helium.

Over billions of years, these gasses kept combining to form stars. Generations of stars were born and died. They died in spectacular explosions called novas. These novas released clouds of dust and gas into the universe. They also released other elements, like metals. These elements had been created within the stars themselves. In fact, almost all the elements we know today were originally created by novas. This went on for about 10 billion years.

Then, about 5 billion years ago, something really important happened. At least it’s important to us. One of these clouds of dust and gas began to collapse. This cloud of interstellar dust and gas is what’s known as the Solar Nebula. As the Solar Nebula collapsed, it began to flatten and rotate like a disk or Frisbee. In its center, a new star was born. That star is our Sun. Its official name is Sol. The cloud of dust and gas rotating about it (the Solar Nebula) became our Solar System.

Here is how astronomers think it may have happened.

As the Sun got bigger and hotter, the disk around it got smaller and cooler. As the disk condensed and cooled, the gasses inside it turned into solids. If you have trouble imagining how a gas could turn into a solid, just think of how steam condenses into water. Then – if the temperature gets cold enough – it turns into ice.

So now, instead of gasses rotating around the Sun, there were billions of solid particles. At first these particles were very tiny. But they began to stick together to form chunks of matter. Over millions of years these chunks got bigger and bigger. Eventually they became planets. Earth is the third planet from the Sun.

There are nine planets in our Solar System. Beginning with the planet closest to the Sun, these planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Neptune, Uranus and Pluto. And no, Pluto was not named for a Walt Disney ™ cartoon character; it was named for a god from Roman mythology. In fact, most of the planets are named for Roman gods, who were pretty amazing characters themselves. Check them out at http://www.messagenet.com/myths/

Our Solar System still rotates around the Sun. In addition to the planets, it contains moons, asteroids and comets. And, on the Earth at least, people.

The early Earth was nothing like the Earth we know today. It was originally a round ball of homogeneous material. That means it had the same chemical composition all the way through. But for its first 10 to 20 million years, the Earth was constantly being hit by meteors and other objects from space. This bombardment created a lot of heat. As layers of new material were added to Earth’s surface, this heat was pushed inside.

Heat was also generated by the decaying isotopes of radioactive elements within the Earth itself. (An isotope is a slightly different version of an element. Many elements have isotopes. An isotope can be either lighter or heavier than the standard element because of the number of neutrons in its atom).

Anyhow, because of all this heat, Earth’s temperature rose so high that one of its elements melted and turned into a liquid. (Remember, most of the elements had come from star explosions -- novas). The element that turned to liquid was iron. This liquid iron was so dense it sank to the center of the Earth, where it formed a metallic core. This pushed the lighter, less dense elements out toward the surface, where they formed a crust.

That crust, the surface of the Earth, is what we walk on today. Although it varies from place to place, the thickness of this crust ranges from about 30 km to 70 km. In between the crust and the core of Earth, there is another layer called the mantle, which is about 3000 km thick. This mantle is more dense than the crust but less dense than the core. The core is also about 3000 km thick, which gives the Earth a radius of just over 6000 km.

Although most scientists agree on this broad outline of how our Earth and Solar System came to exist, they are still trying to figure out the details. There are many mysteries. Those mysteries are what some of our space missions are all about -- because going out in space is like going back in time. It’s the way we discover our astronomical history.

For example, The Hubbell Space Telescope can show us what the Solar Nebula looked like by taking pictures of other nebulae. You’ve probably seen Hubbell’s pictures on television. And another space mission, Genesis, is going way beyond Earth to investigate something called the solar wind. Scientists think that the gasses and elements in this solar wind may be the very same gasses and elements that made up our original Solar Nebula.

To learn more about the Solar Nebula and the Formation of the Earth, go to:

http://www.jpl.nasa.gov/solar_system/features/mysteries_solarnebula.html (The Solar Nebula)

Experiments for Home and Classroom

There are 9 planets in the Solar System, with no two alike. In this experiment, students discover how old they would be, and how much they'd weigh, on other planets. This is a great way to lose weight without dieting. Click:

• http://www.exploratorium.edu/ronh/age/index.html 
• http://www.exploratorium.edu/ronh/weight/index.html

For a guided tour of the night sky (complete with free sky maps), click: http://space.about.com/od/backyardscience/ss/15minutenitesky.htm 
 

One of the most fascinating planets to Earthlings is Mars, our nearest planet. In this experiment, students simulate the atmosphere of Mars in a jar. The instructions must be followed carefully (this experiment is not for young children). Click: http://www.mit.edu/~goodmanj/madsci/898132128.Ot.r.html
 

Continuing with Mars, this experiment teaches students how to build a paper model of the NASA's Mars Polar Lander. Instructions are also given for a model of the Cassini spacecraft. The Cassini model is good enough to eat -- because it's made of gingerbread. Click:
http://solarsystem.nasa.gov/kids/papermodels.cfm

For older students, here are scale models to build of many NASA spacecraft. These models are so exact many NASA scientists refer to them when it's time to make adjustments to the real thing. Click: http://www.jpl.nasa.gov/scalemodels

Many things in the Solar System can only be seen with a telescope. Telescopes are expensive, but a man named Bill Dobson has designed one that families can make for themselves at home. Click: http://members.aol.com/sfsidewalk/cdobplans.htm 

Students are invited to build a virtual Solar System online by completing this Solar System Jigsaw Puzzle. Choose "Planet" after you click:
http://www.bbc.co.uk/science/space/playspace/games/jigsaw/jigsaw.shtml 

Here are two simple experiments that show (a) how gravity causes a moving object like the Space Shuttle to go into orbit around the Earth and (b) why astronauts are weightless in space. Visit the Bill Nye the Science Guy site. First, go to "home demos" (Hd) and then to (1) Planetary Science (2) Space Science (3) Orbiting Marbles and/or (4) Weightless Clothespin. Click: http://www.billnye.com/flash.html

Now let's do Practice Exercise 1-1 (top)

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