Why don't we feel the Earth moving?

Even though we constantly move at a high rate of speed, we don't feel it, just as we don't feel the speed at which we're flying in an airplane or driving in a car. It's only when there is a sudden change in speed that we notice, and if the Earth made such a change we would certainly feel it.

Does the Earth spin at a constant rate?

The rotation of the Earth actually has slight variations. Motion and activity within the Earth, such as friction due to tides, wind, and other forces, change the speed of the

How was the circumference of the Earth determined?

The Greek geographer and librarian at the Great Library of Alexandria, Eratosthenes (c.273—c.192 b.c.e.), was aware that the sun reached the bottom of a well in Egypt only once a year, on the first day of summer. The well was near Aswan and the Tropic of Cancer (where the sun is directly overhead at noon on the summer solstice). Eratosthenes estimated the distance between the well and Alexandria based on the length of time it took camel caravans to travel between the two places. He measured the angle of the sun's shadow in Alexandria at the same time as the well was lit by the sun, and then used a mathematic formula to determine that the circumference of the Earth was 25,000 miles (about 40,000 kilometers)—amazingly close to the actual figure!

planet's rotation a little. These changes only amount to milliseconds over hundreds of years but do cause people who keep exact time to make corrections every few years.

What is the axis of the Earth?

The axis is the imaginary line that passes through the north and south poles about which the Earth revolves.

What is inside the Earth?

At the very center of the Earth is a dense and solid inner core of iron and other minerals that is about 1,800 miles (2,896 kilometers) wide. Surrounding the inner core is a liquid (molten) outer core. Surrounding the outer core is the mantle, which makes up the bulk of the interior of the Earth. The mantle is composed of three layers—two outer layers are solid and the inner layer (the asthenosphere) is a layer of rock that is easily moved and shaped.

If I dug through the Earth, would I end up in China?

If you are in North America and you were able to dig through the Earth (which is impossible due to such things as pressure, the molten outer core, and solid inner core), you would end up in the Indian Ocean, far from land masses. If you were really lucky, you might end up on a tiny island, but you're surely not going to end up in China. The points at opposite sides of the Earth are called antipodes. Most antipodes of Europe fall into the Pacific Ocean.

What is the mid-Atlantic ridge?

We don't get to appreciate the beauty of this huge mountain range because it's located at the bottom of the Atlantic Ocean (with one exception: Iceland is a part of the ridge).

The ridge is a crack between tectonic plates where new ocean floor is being created as magma flows up from under the Earth. As more crust is created, it pushes the older crust further away. The new crust at the ridge piles up to form mountains and then begins to move across the bottom of the ocean. Because the Earth can't get larger as more crust is created, the crust eventually has nowhere to go except back into the Earth. This is where subduction occurs.

What is subduction?

When two tectonic plates meet and collide, crust must either be lifted up, as in the case of the Himalayas, or it must be sent back into the Earth. When crust from one plate slides under the crust of another, it is called subduction, and the area around the subduction is called a subduction zone.

What is the North Magnetic Pole?

The North Magnetic Pole is where compass needles around the world point. It is located in Canada's Northwest Territories at about 71 degrees north, 96 degrees west (latitude and longitude), about 900 miles (1,450 kilometers) away from absolute North Pole. It moves continuously, so to determine true north, look at a recent topographic map for your local area. It should note the "magnetic declination," which means the degrees east or west that you'll need to rotate your compass to determine which way is actually north.

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