Earth crust

The continents of the old world (The 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, separating the Americas from Africa and Europe. Alaska and Siberia were once joined, but at present Alaska and Siberia are separated by the Bering Strait. The crust of the earth is a relatively thin layer. Scientists 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’. The oldest rocks found so far are thought to be about 3850 million years old, so the earth had a solid crust by then. Some meteorites and pieces of moon rock are probably 4600 million years ago, so scientists think that the earth formed about 4600 million years ago. Scientists measure the earth’s age by studying the rate of decay of radioactive elements with special equipment. This technique is called carbon-dating.

Volcanoes

The lava of volcanoes is molten rock, called magma. Some magma rises straight from the earth’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 nearly molten. Magma contains several gases, and bubbles of this expand near the surface and drive the magma out as an eruption. Volcanic eruptions vary from place to place, mainly according to how fluid or gaseous the lava is. The highest active volcanoes on land are in the Andes, in South America. The highest of these is Ojos Del salada, which is 6885 meters high. But even larger volcanoes rise from the floor of the Pacific Ocean and form the islands of Hawaii. Mauna Loa, on Hawaii, is probably the largest active volcano in the world. It rises 4170 meters above sea level, but its base is 5180 meters below sea level. This base is roughly oval in shape: 119 kilometers long and 85 kilometers across. The lava from Hawaiian volcanoes is very liquid and flows for long distances. Mauna Loa erupts about every 3.5 years. The near by Kilauea crater, south- east of the main volcano, is filled with red-hot lava.

Clouds which we cans see

A cloud is made up of tiny droplets of water or ice. When clouds form, the invisible water vapor in the air condenses into visible droplets of water. All air contains water vapor. 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 cools down when it rises, because the higher in the atmosphere it goes, the cooler it gets. When it rains, tiny droplets in a cloud form bigger drops which fall to earth. The following are the kinds of clouds that we can 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 height. Cirrostratus is a thin, almost transparent layer of cloud at a higher level. Nimbostratus forms at a lower level, while stratus clouds are layers with in 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 cloud high in the sky.

Glaciers on Earth

A glacier is like a great river of ice. Glaciers appear 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 added at the top, the glacier would move forward under its own weight. Most of the glaciers present today are the one left from the last age in the past two million years there have been five glaciations. Ice- sheets spread from mountain areas and from the Artic to cover most of Europe. The ice covers only 10 percent of the land surface. Most of the world’s ice is in Antarctica. The artic has only 12 percent, and the rest is in the glaciers, which exist on every continent. The longest glacier is the Lambert - Fisher ice passage in Antarctica, which is 515 kilometers long. Petermanns glacier in Greenland is the largest glacier in the northern hemisphere, 40 kilometers out to sea. If all the ice in the world melted, new land would reveal in the Arctic and the Antarctic and in some mountains. However, large area of the world would be flooded as sea- level arose. Sea- level has changed in the past during glacial and inter- glacial, so it may change in the future. IF the world’s ice melted, sea level would rise by at least 65 meters, Denmark would be flooded, and many great capitals such as London, Dublin, Paris, Rome and Helsinki would drown.

Oceans & sea

The oceans are huge masses of water between continents, but all linked together to form one mass. There are three oceans. The most easterly is the pacific ocean, covering about billion square kilometers; then comes the Atlantic, with around106 million square kilometer and Indian ocean 75 million kilometers and there are two glacier sea, the Artic and Antarctic, covering 70% of the earth’s surface, altogether. In 1951, the survey ship challenger has found the deepest part of the ocean. Echo- soundings showed part of the Mariana Trench, south of Japan, to be 10,900 meters deep. In 1960, the US navy bathyscaphe Trieste descended to the bottom of the challenger deep. The Mariana Trench is one of many deep trenches around the edges of the Pacific Ocean. These V- shaped trenches are parallel to a continent or line of islands. All water contains salt. The taste depends on the quality and the water in which it is dissolves. In the sea, the saltiness depends on the temperature, the rivers flowing into it and the currents. With high temperatures, water evaporates and the salt gets very concentrated. River brings clear water, so a sea, which has a lot of river water, has less salt than one where few rivers flow. The currents mix the waters and so dilute the quantity of salt.

Temperature range on Earth

A temperature range is the difference in temperatures. It can be daily, between day and night; monthly, between the hottest and coldest day; and a yearly temperature range between the coldest and hottest months. The difference in temperature in various places depends on the latitude and distance from sea. The Sahara Desert, for example, has a daily temperature range; it is so hot by day, yet very cold at night. The coldest place on earth is the Antarctic, where temperatures can often go as low as 78 degree below zero, Celsius. Then is the Siberia with 50 degree Celsius below zero. The coldest cities in Europe, based on average temperatures during the coldest months, are Archangel in Russia with 13 degree Celsius below zero, followed by Montreal, Canada, with 10 degree, Beijing with 4 degree and Tashkent with 1 degree Celsius. The highest shade temperature on record is 58 degree Celsius at Aziziah in the Sahara desert in Libya. The 56 degree Celsius recorded in Death Valley in the USA in July 1913. The eastern Sahara has more sunshine than anywhere else does: sunshine has recorded for 4300 hours in a year, which is an average of 11 hours 47 minutes per day.

Thunder... Lightning...

Lightning is a huge spark of electricity. Thunder is the sound the air makes as it suddenly heated up by lighting. They both happen at the same time, but as light travels faster than sound; we see the lightning first and then hear the thunder. When lightning heats up the molecules of air along its path thunder appears. The heated molecules expand, collide with cooler molecules and set up sound waves. Light travels very quickly, at about 300,000 kilometers per second. Sound is slower, traveling at about 20 kilometers per minute. In the air, there are millions of particles with positive and negative electrical charges. When the big storm clouds gather, the charged particles become more numerous and concentrated, becoming stronger and stronger, until a spark shoots across the space in between lightning. Lightning can happen with in a cloud, between two different clouds and between a cloud and the ground. A lightning conductor is a metal pole, which is set into the ground, going up the side of a building to the roof. In a storm, the air is full of electricity charges of this electricity are what we call lightning. It attracted to the points of objects, so the tip of the conductor attracts the lightning, taking it down to earth, and the building not struck. The lightning conductor invented by the American Benjamin Franklin.