Saturday, January 5, 2008

Inside the Earth

The centre of the Earth is very hot. This heat produces enough energy to keep the ground under your feet constantly moving as the major land masses, or continents, are carried slowly along on a lower layer of semi-liquid rock. This movement causes the continents to be pulled apart in some places, creating new oceans. In other places, they collide and create mountain ranges.

A shifting world
Scientists have discovered that around 250 million years ago all of today's main continents were joined together. Animal alive at that time, such as the dinosaurs, were able to move freely across this huge single landmass. By 200 million years ago, it was starting to break up.

What is the Earth made of?
The Earth has an outer layer of solid rock called the crust (5-60 km/3-37 miles thick), a middle layer of hot, semi liquid rock called the mantle (2900 km/1800 miles thick), and a very hot liquid centre, the core (3470 km/2160 miles in radius). Inside the Earth, the temperature increase rapidly towards the centre, where it is nearly as hot as on the surface of the Sun.
The solid crust is broken into pieces, called plates, which float on the mantle. Some plates are covered by oceans, others by the continents. The plates fit together like a jigsaw, and the places where they meet are called plate boundaries. In some places, two plates push together and one slides over the top of the other. Along some boundaries under the ocean, the plates are moving apart.

250 million years ago
North and South America, Europe, Asia, Australia and the Antarctic formed one big continent called Pangaea. The rest of the Earth was covered by an ocean called Panthalassa.

135 million years ago
Africa and South America began to split apart as the South Atlantic opened up. The North Atlantic formed between North America and Europe.

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Wednesday, December 26, 2007

The power of the Moon
Many animals use the Moon as a clock or compass. Night-flying birds, such as migrating thrushes, time their journeys to navigate by moonlight.

The breeding habits of many sea creatures are guided by the Moon. This is because the Moon and Sun cause the movement of the tides. On May and June nights the tides can be exceptionally high, and horseshoe crabs choose this time to lay their eggs in nests in the sand. High tides give the buried eggs some protection from predators.

Longer Days
Days are getting longer, due to the pull of the Moon and the Sun. As the gravity of these two heavenly bodies forces the tides up and down around the Earth, the movement drags on the spinning Earth, slowing it down. Less than two thousandths of a second is lost every 100 years, but in 200 million years time an Earth day will be 25 hours long.

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Friday, December 14, 2007

Why does daylength change through the year?
Earth's tilt is responsible for changing daylength as well as the changing seasons. In summer, when the North Pole tilts towards the Sun, it is light there 24 hours a day. Everywhere else in the Northern Hemisphere has a relatively long day and short night. In winter, the position is reversed. The North Pole tilts away from the Sun and the Northern Hemisphere has a relatively short number of daylight hours. The same situation occurs in the Southern Hemisphere.

Tag :daylength

Wednesday, December 5, 2007

What is an eclipse?
On rare occasions the Sun, the Moon and the Earth are in line with each other. The Moon blocks the light from the Sun, casting a shadow 160 km (100 miles) wide on the Earth. The affected area is plunged into darkness in what is known as a solar eclipse. Because the Earth and the Moon are on the move, solar eclipses last for only 71/2 minutes.

Solar eclipse
When the Earth, the Moon and the Sun are in line, the Moon casts a shadow over part of the Earth's surface.

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Thursday, November 29, 2007

Why does the Moon's face change?
When we look into the sky, the thing that appears to change most from night is the Moon. But the Moon itself does not change shape. What we see is the Sun's light reflected off the Moon (the Moon generates no light of its own),and this reflection changes as the Earth and the Moon move around the Sun. At the beginning, of the lunar month, the new moon, the lit side of the Moon faces away from Earth, so we see nothing. The portion of the Moon that we can see grows, or waxes, first into a thin silver or crescent, then it grows smaller, or wanes, in a reversal of the process.

Tag :moon's face