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Overview
We can dish the real dirt about dinosaurs, thanks to fossils - traces of theses astonishing animals. Dinosaurs did not print newspapers. They did not take family snapshots or videos 65 million years ago. The only proof scientists have of dinosaurs is their fossils, especially bones. They would never have survived billions of years waiting for some human to trip over them. Luckily for paleontologists (scientists who study the past), now and then dinosaurs died, and their bones were covered by mud, or sand. As the bones sat protected from weather, they absorbed minerals from the soil around them. The minerals chemically worked their way into the bones. Millions of years later, we can find them and dig them up. Humans were not around to see what actually killed the ancient dinosaurs. Many scientists think a meteorite, or lots of meteorites, crashed into the Earth. When the space rocks hit the ground, they made big craters and kicked up a lot of dust and dirt. If enough d
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E11. Flight
1993 · 26m
Things that fly need air. Even though we walk through it, breathe it, and sneeze it, air seems to be a whole bunch of nothing. But air is there, and it's powerful. Balloons inflate because air presses on the insides and outsides of the balloon. Air pressure in tires supports the weight of bikes, buses, trucks, cars, and planes. But air doesn't need to be inside something to exert pressure. Air that moves around pushes, too. What do birds, planes, kites, Frisbees, and helicopters have in common? They fly because moving air creates lift, or a push up. Airplane wings are shaped to push air down. The momentum of the air going down pushes wings up. Air above the wing gets going faster than the air underneath. Fast-moving air zips along, without pushing as hard side to side or up and down. The slow air pushes up from below harder than the fast air pushes down from above ... and you're airborne! Every flying thing, from the tiniest flying insect to the biggest airplane, us
E22. Earth's Crust
1993 · 26m
Don't just go with the flow. Settle down on the crust. Imagine a world without any crust. There would be no pies, just goopy filling, no bread, no hamburger buns, and no you or me. That's right. You, and every living thing we know of, live on or in the Earth's crust. And, living things need the Earth's crust to survive. Let's look at the science of the surface. By carefully studying the Earth's surface, scientists have discovered that the Earth is made up of gigantic layers. At the center of the Earth, there is a core – a big ball of solid metal mostly iron. The core is surrounded by a layer of liquid iron and other minerals. We usually just call it the outer core. The next layer, around the outer core is called the mantle. You may have seen a mantle above a fireplace. Well, the mantle is above the Earth's hot core places. The mantle is gooey hot nearly melted rock that flows the way asphalt does on a hot summer day. Scientists often say that the mantle is plastic. It
