Why do Glaciers appear?

A Glacier is like a great river of ice . glaciers appears when more snow falls than melts every year. The snow collects , squeezing the lower layer hard. it turns ice and forms a glacier.

All the time snow is being added at the top , the glacier will move forward under its own weight. Most glaciers today are left over from the Last Ice age. In the past two million years there have been five glaciations areas and from the Artic to cover most of Europe .

Why do lakes Sometimes Disappear ?

Many lakes have vanished . Some have been filled up, the water of others has flowed away,and other lakes in very hot countries have simply dried up.

Lakes can be filled up with material brought down by rivers. Deltas in a lake can eventuallyfill up the whole lake, which becomes an almost flat plain. Some lakes dry up because of evaporation, and some disappear and return, such as lake Eyre in Australia .It is Huge lake, but it disappears in dry weather.

Why do some rivers have Deltas ?

A Delta is shaped like a triangle , which is also the shape of the Greek letter D, called Delta. A river delta is caused by deposits at the mouth of the river. This happens when the river transports more slit to its mouth than can be removed by currents or tides.

The Mediterranean Sea has a very small tidal range , so big rivers like the Nile and the Rhone have very big Deltas. Deltas are less common rivers that flow to oceans and tidal seas.

What kinds of Clouds can we see ?

Clouds are made of millions of tiny water droplets or ice crystals suspended in the air. They are named according to their shape and heights.

Cirrostratus is a thin , almost transparent layer of cloud at a high level. Altostratus is a thicker layer of cloud at a higher level. Nimbostratus forms at a lower level, while stratus clouds are layers within 500 meters of the Earth's surface .'Puffy' clouds, known as cumulus clouds, are called altocumulus at a high level. When they join together they form stratocumulus.
Cumulonimbus are towering thunder clouds. A third type of cloud is cirrus, wisps of clouds high in the sky.

What is the Atmosphere Made Of ?

The Atmosphere is the air which surrounds the planet Earth. The gases in the air allow plants,
animals and humans to live. The dampness ad movement of the air near the Earth causes our
weather. The atmosphere also shields us from the Sun's harmful rays and from fallingmeteorites.

Air is made up of many gases. The most common are nitrogen(78%) and oxygen (21%).

There are small amounts of other gases, including argon, water vapor and carbon dioxide.

Why do clouds Form ?

A cloud is made up of tiny droplets of water or ice. When cloud forms, the invisible vapor in the air condenses in to visible droplets of water.

All air contains water vapors . Warm air can hold more water vapor than cold air. if the air Cools down, it cannot hold so much water vapor, and it turns into tiny droplets of water. Air cooled down when it rises, because the higher in the atmosphere it goes, the cooler it Gets, When it rains, tiny droplets in a cloud from bigger drops which fall to earth.

Why Do the Tides Rise And Fall ?

The water in the oceans is held close to the earth by gravity. But the Moon and Sun also have some 'pull' on the earth. The Moon's gravity affects water in the oceans. The sea is 'pulled' slightly towards the Moon, causing a bulge, or high tide. On the opposite side, the sea is pushed away, causing a second bulge.

High tided occur twice in about 25 hours. This is because at the same time as the earth is rotating on its axis , the Moon is traveling round the Earth(every 27 days).

Why do earthquakes occur only in some parts of the world?

The map shows where earthquakes have happened . These occur near the edges of the Rearth's Crustal plates.

The plates are slowly moving together or apart. For instance , one zone encircles the Pacific. Here , the floor of the Pasific is being pushed down under the continents, and this gradual movement of Pacific plates agaist the continental plates causes earthquakes. Other zones are in the Mediterranean and the Atlantic.

Where do Gysers occur ?

All geysers occur in areas of volcanic activity, but not all volcanic areas have geysers.They only occur where water can soak through cracks in the rocks and collect underground

Here the water is heated under pressure, and as it starts to bubble out there is a sudden gush of steam and hot water high in to the air.

Why do volcanoes erupt?

The lava of volcanoes is molten rock , called magma.Some magma rises straight from the Eart's
mantle to the surface .Some is stored in a magma chamber in the crust, where the gases collect
and help to drive the magma out.

The upper part of the mantle, under the Earth's crust, is nealry molten. Magma contains
several gases, and bubbles of this expand near the surface and drive the magma out as an eruption . Volcanice eruptions vary from place to place, mainly according to how fluid or gasous the lava is .

The crust of the Earth is a relatively thin layer. Scientist believe it is divided into huge sections called "plates". These are moved very slowly by convection currents inside the Earth.

The scientist Alfred Wegener suggested in 1915 that the continents might have moved.
He had noticed that their shapes fit together like a jigsaw. His Theory was called"Continental Drift"

Why are Fossils important to geologists?

Fossils help geologists to put different kinds of rocks in the same age group. Fossils
also give information about the conditions that existed when they were alive. and
similar fossils in different places help in the study of continental drift.

The most useful fossils are of plant and animals which lived in a wide variety of places ,
but only for a short period of time these are called index fossils.

Why did dinosaurs die out so suddenly?

Dinosaurs became extinct about 65 million years ago, at the end of Cretaceous times.
They had existed for 130 million years. No one knows why they died out.

Many other types of animals died out at the same time as the dinosaurs, including
flying and sea reptiles. but few reptiles did survive , including turtles, lizards
and snakes . there are many theories to explain why the dinosaurs died out ,including
changes of climate and vegetation, cold winters, new parasites and diseases.

When did Sea Charts Come Into Use?

SEA CHARTS

The earliest record of a sea chart dates from 1270 when Louis IX of france studied a chart on
board a Genoese ship during the Eighth Crusade. The earliset navigators kept close to
land or drifted with ocean currents.

Once the compass was used , ships could sail more directly from one port to another.
The Chinese and Arabs may have used sea charts befor Europeans, but none survive
From about 1200, compassed and rudders were used on european ships . Navigators used
portolani, books which listed ports,landmarks, distances and navigational advice.

When did the old and new worlds seperate?

The continents of the old world (Europe, Asia and Africa ) and the New world
The Americas ) have been slowly drifting on the surface of the Earth since our
planet became solid . In the last 150 million years, the Atlantic has gradually
opened up, seperating the Americas from Africa and Europe.

Alaska and Siberia were once joined , but at present Alaska and Siberia
are seperated by the Bering Strait.