Friday, February 25, 2011

I Wonder ...... Earth

When our "I Wonder" session began this week, we all sat down in a circle and the kids did some "wondering," and I reminded them that we had planned to talk about one of the "wonders" from last week: how the Earth came to be the Earth! 

I had my story ready:

A long, long, long, long, long time ago(!) there wasn't any Earth. All there was, was just a lot of dust and rocks, floating in space.

Then, this one fairly big rock came along, and other rocks and dust started to stick to it. As they did, it got bigger and bigger, and the bigger it became, the more the other rocks and dust wanted to stick to it, so it kept getting bigger and bigger until eventually it was HUGE! And that HUGE rock is what we now call Earth.

Now, I said that the other little rocks and dust started to stick to the bigger rock. But how do we know that happened? We know because it still happens! We can even make that happen here in the classroom, RIGHT NOW!

(Have the children pick up small objects - pencils and so forth.)

Okay, now let's pretend that the pencils and the rulers are just like rocks and dust in space. (If anyone is really dubious, you can always get them some rocks.) What happens if you let them go?

(The children let them go. They fall.)

See? Everything wants to stick to the Earth! In fact, WE even want to stick to the Earth! (Jump up, fall back down!) Does anyone know a name for that? It's called Gravity.

Now, does anyone know anything else that things like to stick to? (Discussion - and introduce the magnet.)

Magnets don't have gravity, they have magnetism. It's different because only metal wants to stick to a magnet, but EVERYTHING wants to stick to the Earth. But we can use a little magnet to let you imagine what it looked like when the Earth was just starting to grow.  (Show the magnet. Put it under the paper. Explain that the iron filings are dust, but they're made of metal so that they want to stick to the magnet. Sprinkle filings over the paper, very slowly, explaining that these are the pieces of dust passing by. As you do so, filings landing near the spot where the magnet is below the paper, will start to gather in a clump over the magnet. The area nearby will have very few filings on the paper, although filings landing farther away will stay where they are. The clump of filings represents the rocks gathering to form the early Earth, and the clear space around the clump shows why the Earth isn’t growing much today – all the rocks that could have fallen down have already fallen down.) 

You may want to re-do the "things falling" demonstration. It's pretty cool because they can see for themselves how the rocks stick to the Earth - and to see that they do, too.


Questions you might be asked:

Q: Where did the dust come from?
A: We don't really know! We know that some of it came from stars, like the sun, very far away. And scientists think that, originally, everything began in a giant explosion called the Big Bang, but how that happened is still a mystery. Maybe one of you will eventually figure it out!

Q: Why does everything want to stick to the Earth?
A: Gravity means that when something is really, really big, small things want to stick to it. Things want to stick to the Earth, but things near the Moon want to stick to the Moon. And, in fact, things near the Sun want to stick to the Sun (which is really hot, so I'm glad I'm not standing on it)!

Q: But if the Earth started off as a small rock, why did things want to stick to it then, when it was small?
A: Well, back then only very very tiny things stuck to it. But every time they did, it got a little bigger. And as it got bigger, slightly bigger things stuck to it. It was a bit like making a snowman, when you start off with a snowball and roll it on the ground (not all the children may know this, but some will). At first you roll it and roll it but only a little snow sticks to it, and it stays small for a long time. But then, as it gets bigger, it grows faster and faster, and soon it gets really big.

Q: Is the Earth still getting bigger?
A: Not much anymore, but yes. Almost everything in the area, small enough to fall down onto it, has already fallen down! But sometimes a passing rock, floating past in space on its way from somewhere else, will get pulled down. At night, if it's really dark out (like when you're in the countryside), you sometimes see a falling star. That's a rock, falling down onto the Earth, and making it a little bit bigger!

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