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Old Friday, November 02, 2007
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Planet Earth: Facts & Figures

What is the biggest continent?
Asia covers an area of 44,009,000 sq km. The other continents, in order of size, are Africa (30,246,000 sq km), North America (24, 219,000 sq km), South America (17,832,000 sq km), Antartica (14,000,000 sq km), Europe (10,443,000 sq km), and Australia (7,713,000 sq km).
Where is the world's lowest point on land?
The shoreline of the Dead Sea, between Israel and Jordan, is 400m below the sea level of the Mediterranean Sea.
What is the world's largest island?
Greenland covers about 2,175,000 sq km. (Geographers regard Australia as a continent and not as an island,)
What is the world's largest river basin?
The Amazon river basin in South America covers about 7,045,000 sq km. The Madeira River, which flows into the Amazon, is the world's longest tributary at 3,380 km.
What is the world's largest bay?
Hudson Bay in Canada covers an area of about 1,233,000 sq km. It is linked to the North Atlantic Ocean by the Hudson Strait.
Which is the deepest lake?
Lake Baikal, in Siberia, eastern Russia, is the world's deepest lake. The deepest spot measured so far is 1,637 m.
How much of the world is covered by land?
Land covers about 148,460,000 sq km, or 29% of the world's surface. Water covers remaining 71%.
What is the world's higest peak?
Mount Everest on Nepal's border with China reaches 8,848 m above sea level. Measured from its base on the sea floor, Mauna Kea, Hawii, is 10,203 m high. But only 4,205 m appear above sea level.
What is the world's largest high plateau?
The swept Tibetan Plateau in China covers about 1,850,000 sq km.
What is the largest island body of water, or lake?
The salty Caspian Sea, which lies partly in Europe and partly in Asia, has an area of about 371,380 sq km. The largest fresh water lake is Lake Superior, one of the Great Lakes of North America. Lake Superior has an area of 82,350 sq km.
Is there a lake under Antartica?
Scientist have found a lake, about the size of Lake Ontario in North America, hidden under Antartica. It may contain creatures that lived on Earth millions of years ago.
Where do most people live?
The continent with the largest population is Asia, which has more than 3,000 million people. Europe ranks second in world population, followed by Africa, North America, South America and Australia. The continent Antartica has no permanent population at all.
Which is the world's longest river?
The Nile in northeast Africa is 6,617 km long. The second longest river, the Amazon in South America, discharges 60 times more water than the Nile.
What is the deepest cave?
The Reseau Jean Bernard in France is the deepest cave system. It reaches a depth of 1,602 m.
What is the world's largest desert?
The Sahara in North Africa, covers an area of about 9,269,000 sq km. This is nearly as big as the United States.
What is the world's largest ocean?
Pacific ocean covering an area of 165,241,000 sq km, followed by Atlantic ocean (81,500,000 sq km), Indian ocean (73,452,000 sq km), and Artic Ocean (14,089,600 sq km).
What is the world's largest sea?
Arabian sea covering an area of 3,864,000 sq km.
What is the world's highest waterfall?
Angel Falls, in Venezuela, with a hight of 979 m.
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Planet Earth: Rocks & Minerals

What are the three main kinds of rocks?

There are igneous, sedimentary and metamorphic rocks. Igneous rocks are formed from cooled magma. Sometimes it cools on the surface to form rocks such as basalt. Other magma cools underground to create rocks called granites. Many sedimentry rocks are made from worn fragments of other rocks. For example, sandstones is formed from sand. Sand consists mainly of quartz, a mineral found in granite. And some limestones are made from the shells of sea creatures. Metamorphic rocks are rocks changed by heat and pressure. For example, great heat turns limestone into marble.
What are elements and minerals?
Earth's crust contains 92 elements. The two most common elements are oxygen and silicon. Also common are aluminium, iron, calcium, sodium, potassium and magnesium. These eight elements make up 98.59% of the weight of the Earth's crust. Some elements, such as gold, occur in a pure state. But most elements are chemical combinations of elements. For example, minerals made of oxygen and silicon, often with small amounts of other elements, are called silicates. They include feldspar, quartz and mica - all found in granite.
Is coal a rock?
No. Although coal is sometimes called an organic rock, it is not a proper rock as rocks are inorganic (lifeless). Coal, like oil and natural gas, was formed millions of years ago from the remains of once-living things. That is why coal, oil and gas are called fossil fules.
Can minerals make you invisible?
No, although in the Middle Ages people thought that you would become invisible if you wore an opal wrapped in a bay leaf.
What is the hardest mineral?
Diamond, a pure but rare form of carbon, is formed under great pressure deep inside the earth. It is the hardest natural substance.
What are the most valuable minerals?
Gemstones such as diamonds, rubies, sapphires and emeralds are valuable minerals. Gold and silver are also regarded as minerals, although they occur as free as elements.
What are the most common rocks?
Sedimentary rocks cover 75% of the Earth's land surface. But igneous rocks make up 95% of the rocks in the top 16 km of the Earth's crust.
What are birthstones?
Birthstones are minerals that symbolize the month of a person's birth. For example, garnet is the birthstone for January, while ruby is the stone for people born in July.
What common rocks are used for buildings?
Two sedimentary rocks, limestones ans sandstones, and the igneous rock granite are all building stones. The metamorphic rock marble is often used to decorate buildings.
Are some minerals more plentiful than others?
Many useful minerals are abundant. Other less common, but important, minerals are in short supply and are often recycled from scrap. Recycling saves energy, which has to be used to process metal ores.
Which elements are mainly found in the Earth's crust?
The bulk of the Earth's crust is oxygen (46%) and silicon (28%), mostly combined in rocks or sand (silicon oxide). Clays are made of silicon and oxygen combined with aluminium (8%), the third most common element. Apart from these, 5% iron, 3.5% calcium and 9.5% othere elements.
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Planet Earth: The work of ice

How does ice shape the land?
In cold mountain areas, snow piles up in hollows. Gradually the snow becomes compacted into ice. Eventually, the ice spills out of the hollows and starts to move downhills to form a glacier. Glaciers are like conveyor belts. On the tops of glaciers are rocks shattered by frost action that have tumbled downhill. Other rocks are frozen into the sides and bottoms of glaciers. They give glaciers the power to wear away rocks and deepen the valleys through which they flow. Ice-worn valleys are U-shaped, with steep sides and flat bottoms. This distinguishes them from V-shaped river valleys.
Which are the world's largest bodies of ice?
The largest bodies of ice are the ice sheets of Antarctic and Greenland. Smaller ice caps occur in the Arctic, while mountain glaciers are found around the world.
What are erratics?
Erratics are boulders made of a rock that is different from the rocks on which they rest. They were carried there by moving ice.
When did the last ice age take place?
The last ice age began about 1.6 million years ago and ended 10,000 years ago. The ice age included warm periods and long periods of bitter cold.
What is an ice age?
During ice ages, average temperatures fall and ice sheets spread over large areas that were once ice-free. Several ice ages have occurred in Earth's history.
How can we tell that an area was once covered by ice?
Certain tell-tale features give this away. Mountain area contain deep, steep-sided valleys that were worn out by glaciers. Armchair-shaped basins where glaciers ice once formed are called cirques. Knife-edged ridges between cirques are called aretes, while peaks called horns were carved when three opr more cirques formed back-to-back. Boulders and other material carried by ice is called moraine. Moraine ridges show that ice sheets once reached that area.
What are fiords?
Fiords are deep, steep-sided valleys that wind inland along coasts. They were once river valleys that were deepened by glaciers during the last Ice Age.
How much of the world is covered by ice?
Ice covers about 10% of the world's land area. But during the last Ice Ages, it spread over much of northern North America and Europe. The same ice sheet reached what is now New York City in America, and covered London.
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Planet Earth: Fossils

What are fossils?
Fossils are the impressions of ancient life preserved in rocks. When dead creatures are buried on the sea floor, the soft parts rot away, but the hard parts remain. Later, the mud and sand on the sea bed harden into rock. Water seeping through the rock dissolves the hard parts, forming fossil moulds. Minerals fill the moulds to create casts, which preserve the shapes of the hard parts. Other fossils include outlines of leaves turned to stones, and insects in amber.
What is amber?
Amber is a hard substance formed from the sticky resin of trees. Tiny animals were sometimes trapped in th resin. Their bodies were preserved when the resin hardened.
Has flesh ever been preserved as a fossil?
In Siberia, woolly mammoths, which lived more than 40,000 years ago, sank in swampy ground. When the soil froze, their comlete bodies were preserved in the icy subsoil.
What are trace fossils?
Trace fossils give information about animals that lived in ancient times. Animal burrows are sometimes preserved, giving scientists clues about the creatures that made them. Other trace fossils include footprints preserved in hardened mud and quickly buried under more mud.
What is eohippus?
Eohippus is the name of the dog-sized ancestor of the horse, which lived about 55 million years ago. Fossil studies of eohippus and its successors have shown how the modern horse evolved.
What is carbonization?
Leaves usually rot quickly after plants die. But sometimes they float to the bottom of the lakes and are buried under fine mud. Sediments above and below the leaf are gradually compressed and hardened into sedimentary rocks. Over time, bacteria gradually change the chemistry of the leaf until only the carbon it contains remains. The shape of the leaf is preserved in the rock as a thin carbon smear. This process is called carbonization.
How are fossils turned to stone?
When tree trunks or bones are buried, minerals deposited from water sometimes replace the original material. The wood or bone is then petrified, or turned to stone.
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How do you date fossils?
Sometimes, dead creatures are found buried under volcanic ash. The ash sometimes contains radioactive substances that scientists can date. Hence, they can work out the time when the animals lived.
What is carbon dating?
Plants and animals absorb and give out carbon-14 while they are alive, so the percantage of carbon-14 in their tissues stays constant. When they die, the percentage of trapped carbon-14 reduces as the nuclide decays by beta emission. By measuring the activity of the carbon-14 present in dead plant or animal tissues, it is possible to estimate their age from a decay curve. This is known as carbon dating, and it is one of the methods used by archaeologists to determine the age of ancient remains.
What was piltdown man?
Some bones, thought to be fossils of an early human ancestor, were discovered at Plitdown Common, England, between 1910 and 1912. But Plitdown man was a fake. The skull was human, but the jawbone came from an orang-utan.
What can scientists learn from fossils?
From the study of fossils- know as palaeontology- scientists can learn about how living thing evolved on Earth. Fossils can also help palaeontologists to date rocks. This is because some species lived for only short period on Earth. So, if the fossils of these creatures are found in rocks in different places, the rocks must have been formed at the same time. Such fossils are called index fossils. Important index fossils include species of trilobites, graptolites, brachipods, crinoids, ammonites and belemnites.
How were petrified logs performed?
Petrified logs formed when water replaced the molecules in buried logs with minerals. Slowly, stones replicas of the log were produced.
What are trilobite fossils?
Trilobites were common animals that lived in the sea in the Paleozoic era.
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Planet Earth: Natural Wonders

What are natural wonders?
The ancient Greeks and Romans made lists of the Seven Wonders of the World. They were all made by people. But the Earth also has many natural wonders, created by the forces that countinuously shape our planet. Most list of natutal wonders include the Grand Canyon in the southwestern United States. It is the world's largest canyon and the most awe-inspiring. The canyon is 446 km long and about 1.6 km deep. It was worn down by the Colorado River over the last six million years.
Where do the world's natural wonders occur?
The world's natural wonders can be found in every continent, and some, such as Australia's Great Barrier Reef, occur in the oceans.
Where is the 'Great Pebble'?
The word Uluru is an Australian Aboriginal word meaning 'great pebble'. Also called Ayers Rock, it is the world's biggest monolith (single rock).
Which is the world's highest mountain range?
The Himalayas, in Asia. It contains 96 of the world's 109 peaks that are more then 7,315 m above sea level. One of these peaks is Mount Everest, the world's highest mountain.
Which mountains look like dragon's teeth?
Steep-sided hills made of limestone, found around the town of Guilin in southeastern China. Wearing away by rainwater has made them their strange shape.
Which is the world's mightest river?
The Amazon River in South America contains far more water than any other river. Its river basin (the region it drains) is also the world's largest.
The Amazon drains a huge region that contains the world's largest rainforests.

What is Meteor Crater?
Meteor Crater in Arizona, USA, is a circular depression. It resembles a volcanic crater, but was formed about 50,000 years ago when a meteor hit our planet. The crater is 1,275 m wide and 175 m deep.
Where can you find 'smoke that thunders'?
The local name of the beautiful Victoria Falls on the Zambezi River between Zambia and Zimbabwe is Mosi oa Tunya, meaning 'smoke that thunders'.
The Victoria Falls in Africa is named after Queen Victoria by the explorer and missionary David Livingstone.

What is the Great Barrier Reef?
The Great Barrier Reef is the world's longest group of coral reefs and islands. It lies off the northeast coast of Australia, and is about 2,000 km long.
Which Japenese wonder attracts pilgrims?
Mount Fuji in Japan is a beautiful volcanic cone. Many people regard it as a sacred mountain - a dwelling place for the gods - and they make long pilgrimages to the top.
Where is the Matterhorn?
The Matterhorn is the magnificient mountain on Switzerland's border with Italy. It was created by glaciers wearing away the mountain from opposite sides.
The Matterhorn reaches the hight of 4,478 m above sea level.

How can we protect our natural wonders?
Many people work to protect natural wonders so that they can be enjoyed by people in the future. One important step in protecting them was made in 1872, when the world's first natural park was founded at Yellowstone, site of the famous geyser named Old Faithful, in the northwestern United States. Since then, national parks have been founded around the world.
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Planet Earth: Volcanoes

What makes volcanoes erupt?
Volcanoes erupt when hot molten rock from deep down in the Earth's mantle rises through the Earth's hard outer layer and reaches the surface. The molten rock is called the magma, but when it reaches the surface, it is called lava. It reaches the surface through vents, which are holes in the ground. Lava may burst from a central vent or through side vents.When volcanoes erupt, they may hurl rocks and ash into the air, and lava may flow down slopes. Lava flows burn everything in their path. When lava and volcanic ash harden, they slowly break down to form soil rich in minerals. Clouds of ash often block out the Sun. Ash falls on the land and it may bury towns. Mud flows occur when rain turns the ash into torrents of mud. Most volcanoes occur near the edges of plWhat is a ates. Many rise along the ocean ridges where magma rushes up to fill the gaps formed as plates move apart. Other volcanoes get their magma from the plates that are melted as they are pulled beneath other plates.
What are 'hot spots'?
Some volcanoes lie far from plate edges. They form over 'hot spot' - areas of great heat in the Earth's mantle. Hawaii in the Pacific Ocean is over a hot spot.
What are hot springs and geysers?
These are places where underground water, heated by magma inside the Earth, breaks through to the surface. Warm water bubbles up at hot springes. Geysers hurl boiling water and stream into the air.
What is an extinct volcano?
Volcanoes that have not erupted in recorded history are said to be 'extinct'. This means that they are not expected to erupt ever again.
What is a dormant volcano?
Some volcanoes erupt continuously for long periods. But other active volcanoes erupt only now and then. When they are not erupting, they are said to be dormant, or sleeping.
Do all volcanoes erupt in the same way?
No, they don't. Volcanoes can explode upwards or sideways or erupt 'quietly'. Trapped inside the magma in explosive volcanoes are lots of gases and water vapour. These gases shatter the magma and hurl columns of volcanic ash and fine volcanic dust into the air. Fragments of shattered magma are called pyroclasts, Sometimes, clouds of ash and hot gases are shot sideways out of volcanoes. They pour downhill at great speeds destroying everything in their paths. In 'quietly' erupting volcanoes, the magma emerges on the surface as runny lava and flows downhill.
What are the three main kinds of volcanoes?
The three main kinds are shield volcanoes, explosive volcanoes and intermediate volcanoes.
Shield volcanoes: shaped like upturned shields, are formed by 'quiet eruptions', in which long streams of very fluid are emitted.
Explosive volcanoes: occur when the magma is thick and contains explosive gases. Explosive volcanoes are made of ash and cinders and are steep-sided.
Intermediate volcanoes: are cone-shaped. They are composed of alternating layers of ash and hardened lava.

Do volcanoes do any good?
Volcanic eruptions cause tremendous damage, but soil formed from volcanic ash is extremely fertile. Volcanic rocks are also used in building and chemical industries.
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Planet Earth: The Changing Earth

What are plates?
The earth's hard outer layers are divided into large blocks called plates. These consists of the earth's crust and the top part of the mantle.

How deep are plates?
There are about seven large plates. Their exact thickness is uncertain but they could be up to 145 km in places.

Can plates move sideways?

Plates not only move apart or push against each other, they can also move sideways along huge cracks in the ground called transform faults.

What happens when plates collide?
If this happens along a deep ocean trench, one plate is pulled beneath another, and is melted and recycled. The ocean floor has huge ridges, where plates are moving apart. The gaps are filled with rising magma. Hot liquid rock rises under the ocean ridges. It then spreads out, causing currents that pull the plates apart.
On land, when continents collide, their edges are squeezed up into new mountain ranges. The rocks on the edge of the continents are folded by the pressure of plate movements.


How fast do plates move?
Plates move, on average, between 4 to 7 cm a year. This may sound slow. But over millions of years, these small plates movements dramatically change the face of the earth. Also when plates move, the land is shaken by earthquakes.

How do earth's plates move apart?
Earth's plates float on a partly molten layer within the mantle. Currents in the partly molten rocks slowy move the plates around. Where the plates are moved apart, liquid rock, called magma, rises and plug the gaps. When the magma hardens, it forms new crustal rock.

Who first suggested the idea of continental drift?
In the early 1900s, an American, F.B.Taylor, and a German, Alfred Wegener, both suggested the idea of continental drift. But scientists could not explain how the plates moved until the 1960s, following studies of the ocean floor.

About 280 million years ago, the world's land areas moved together to form one supercontinent called Pangaea. Pangaea began to break apart about 180 million years ago. About 65 million years ago, the Atlantic Ocean was opening up and India was moving towards Asia. Plates movements are still changing the face of our planet.

How do volcanic islands form in the middle of ocean?
Volcanic island form when magma rises from the mantle. Lava (the name for magma when it reaches the surface) piles up until it emerges above sea level.

Have fossils helped to prove continental drift?
Fossils of animals that could not possibly have swum across oceans have been found in different continents. This suggests that the continents were once all joined together and that animals could walk from one continent to another.

Has the earth always looked the same?
If aliens had visited earth 200 million years ago, they would have seen only one huge continent, called Pangaea, surrounded by one ocean. Around 180 million years ago, Pangaea began to break up. By 135 million years ago, a plate bearing South America was drifting away from Africa, creating the South Atlantic Ocean. By 100 million years ago, plates supporting India, Australia and Antartica were also drifting away from Africa, and North America was moving away from Europe.
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Planet Earth: Shaping the land

How does weathering help shape the land?
Weathering is the breakdown of rocks on the earth's surface. The wearing away of the rock limestone is an example of chemical weathering. Limestone consists mostly of calcium carbonate. This chemical reacts with rainwater, which contains carbon dioxide dissolved from the air. The rainwater is a weak acid that slowly dissloves the limestone. It opens up cracks in the surface, wearing out holes that can eventually lead down to huge caves linked by tunnels.

What are springs?
Springs occur when ground water flows to the surface. Springs are the sources of many rivers. Hot springs often occur in volcanic areas, where the ground water is heated by magma.

Can the sun's heat cause mechanical weathering?
In hot, dry regions, rocks are heated by the Sun, but they cool at night. These changes crack rock surfaces, which peel away like the layers of an onion.

What is ground water?
Ground water is water that seeps slowly through rocks, such as sandstones and limestones. The top level of the water in the rocks is called the water table. Wells are dug down to the water table.

Does water react chemically with other rocks?
Water dissolves rock salt. It also reacts with some types of the hard rock granite, turning minerals in the rock into a clay called kaolin.

What are stalactites?
Water containing a lot of calcium carbonate drips down from the ceilings of limestone caves. The water gradually deposits calcium carbonate to form hanging, icicle-like structures called stalactites.

What are stalagmites?
Stalagmites are the opposite of stalactites. They are columns of calcium carbonate deposited by dripping water, but stalagmites grow upwards from the floors caves.

What are pot-holers?
Pot-holers, or swallow holes, are holes in the ground where people called pot-holers can climb down to explore limestone caves. They are formed when the roofs of shallow caves collapse.

What is biological weathering?
Biological weathering includes the splitting apart of rocks by tree roots, the exposing and consequential weathering of rocks by burrowing animals, and the work of bacteria, which also helps to weather rocks.

Can plants change the land?
Plant roots can break up the rock. When the seed of a tree falls into a crack in a rock, it develops roots that push downwards. As the roots grow, they push against the sides of the crack until the rock splits apart.

How quickly is the land worn away?
Scientists have worked out that an average of 3.5 cm is worn away from land areas every 1,000 years. This sounds slow, but over millions of years, mountains are worn down to make plains.

How does the action of frost break up rocks?
At night in the mountains, people may hear sounds like gunshots. These are made by rocks being split apart by frost action (an example of mechanical weathering). As the water in cracks in the rock freezes and turns into ice, it takes up nearly one-tenth as much space again, and so it exerts pressure, widening the cracks until they split apart.
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Planet Earth: The last frontiers

Why are icebergs dangerous to shipping?
Icebergs are huge chunks of ice that break off fom glaciers. They float in the sea with nine-tenths of their bulk submerged, which makes them extremely dangerous to shipping. Icebergs from Greenland have sunk ships off the coasts of North America.
Icebergs in the ocean:- Flat-topped icebergs form off the coast of Antartica. The bulk of the ice in iceberg is hidden beneath the waves.


What it is like around the north pole?
It is bitter cold. The North Pole lies in the middle of the Arctic Ocean, which is surrounded by northern North America, Asia and Europe. Sea ice covers much of the ocean for most of the year. In spring, the sea ice is about 3 m thick in mid-ocean and explorers can walk across it. The Arctic Ocean contains several islands, including Greenland, the world's largest. A huge ice sheet, the world's second largest, covers more than four-fifths of Greenland.

What are the poles?
The earth is always spinning on its axis, giving us day and night. The point at the ends of this axis are the North and South geographic poles.

What animals live in polar region?
Penguins are the best known animals of Antarctica. Polar bears, caribou, musk oxen and reindeer are large animals that live in the Arctic region.

What are ice shelves?
Ice shelves are large blocks of ice joined to Antarctica's ice sheet, but which jut out over the sea. When chunks break away, they form flat, table-topped icebergs. Some of them are huge. One covered an area about the size of Belgium.[/COLOR]

Is the ice around the poles melting?
In parts of Antarctica, the ice shelves began to melt in the 1990s. Some people think this shows that the world is getting warmer because of pollution.

What are magnetic poles?
The earth is like a giant magnet, with two magnetic poles. They lie near the geographic. North and South poles, though their positions change from time to time.

How thick is the ice in antarctica?
The South Pole lies in the cold and windy continent of Antarctica, which is larger than either Europe or Australia. Ice and snow cover 98% of Antarctica, although some coastal areas and high peaks are ice-free. The Antarctica ice sheet is the world's largest, and contains about seven-tenths of the world's fresh water. In places, the ice is up to 4.8 km thick. The world's record lowest temperature, -89.2 degree C, was recorded at the Vostok research station in 1983.

Icebergs :-

Icebergs melt as they float from polar regions and the climate becomes warmer.

Icebergs contain worn rocks that have been eroded from the land.

As icebergs melt, the rocks in the ice sink down and settle on the ocean bed.

High jagged icebergs break away from valley glaciers.
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