My Science School

Poisonous air

The Earth’s original atmosphere was very poisonous. It contained almost no oxygen. It consisted of gases such as hydrogen, helium, methane and ammonia, as well as carbon dioxide. It would have been impossible to breathe in such an atmosphere Lightning and the Sun’s radiation caused chemical reactions in these gases, producing some of the substances characteristic of life, and this may have triggered the development of the first primitive life forms.

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What is an Ice Age?

Ice Ages were periods when large parts of the Earth’s surface were covered by sheets of ice. Each Ice Age has lasted about 100,000 years, with gaps between of up to 20,000 years when the weather was warmer and the ice melted. The last Ice Age ended about 12,000 years ago. Ice ages appear in groups in geological time, each lasting for 20 to 50 million years. The oldest known glacial periods were as long as 2.3 billion years ago. A minor ice age began in the 1500s and lasted for 300 years, during which glaciers were more widespread than at any time for thousands of years.

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Gigantic waterfall!

More than five million years ago, the Mediterranean Sea was a dry basin. Then, movements in the Earth’s crust opened up the Straits of Gibraltar between the land masses of Europe and Africa. The waters of the Atlantic Ocean poured through the gap, flooding the basin. The result was the creation of a gigantic waterfall, at least 800 m high, which let through so much water that the whole of the Mediterranean filled up in few years. 

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What was the Earth like when it was formed?

The Earth had probably existed for around 3,000 million years before the first signs of life appeared. As it cooled after forming from a ball of hot gases, the Earth would have been a relatively smooth sphere. It was covered with shallow seas that contained a mixture of dissolved chemicals, and surrounded by an atmosphere of mixed gases. The atmosphere was full of swirling clouds of vapour, which probably caused huge electrical storms. 

Picture credit: google

 

 

What are metals?

Metals are one of the major groups of elements. Most of them are shiny and hard. Mercury is the only metal that is a liquid at normal temperatures. Most metals can be bent and stretched, and they can be mixed to make alloys.

Metals are usually found with other elements in the form of compounds. Bauxite is an ore, or mixture of substances, that contains aluminium, the commonest metal. It makes up about eight percent of the Earth’s crust. Osmium is the heaviest metal, and is twice as heavy as lead. Lithium is the lightest metal. It is half the weight of the sane volume of water, so it floats in water.

 

 

 

 

 

How much of the Earth is covered by water?

More than two-thirds of the Earth’s surface is covered by seas and oceans. About 72 percent of the Earth’s surface is water. This water is either in the oceans, locked away as ice at the poles, or held as water vapour in the atmosphere. All of the Earth’s water is known as the hydrosphere. 

 

 

 

 

 

 

 

 

Why is the Earth round?

Gravity pulled the Earth and the other planets into a sphere when they were being formed. The Earth is not truly round, but is slightly flattened making it bulge out at the Equator. This effect is due to the speed with which the Earth spins, causing the Equator to try to fly out from the axis of the spinning Earth. It is rather like a heavy object whirling round on the end of a piece of string. The shape of some of the other planets is distorted in the same way.

 

 

What is the Earth made of?

The Earth is made up of elements. These are the simplest possible substances, which are composed of one kind of atom. Elements cannot normally be broken down into other substances, except under the special conditions that you might find inside the hot core of a star. A total of 92 different elements are found in nature. Other elements can be made in laboratories, but they have only a very short life.

Minerals, which make up the solid surface of the Earth, consist mostly of combinations of elements. The minerals gold, diamond and graphite are examples of single elements, while most others contain several elements. 

 

 

 

 

 

What are crystals?

Crystals are solid substances that are naturally formed into regular geometric, angular shapes. All crystals can be classified into seven systems. Sometimes a crystal is formed when water evaporates, and substances dissolved in the water gradually grow into a crystal. Other crystals are formed under great pressure. Diamond crystals are made when carbon dissolves in molten rock deep down below the Earth’s surface. The diamond crystallizes out and is later uncovered on the surface either by volcanic action or by erosion of the Earth’s crust. Other valuable gems are formed in a similar way, and most of them contain compounds of aluminium.

 

 

 

 

 

What is the Equator?

The Equator is an imaginary line drawn around the outside of the Earth. It lies midway between the North Pole and the South Pole, at the Earth’s broadest point.

The Equator was invented by map-makers because it makes a convenient point from which to measure distances, together with the geographic North Pole and South Pole. On a map, the Equator is positioned at 0 degrees of latitude. It divides the Earth into two halves, which we call the north and south hemispheres. 

What is inside the Earth?

The Earth is not solid rock all the way through. It has an inner core of solid rock, which is mostly iron. The temperature here is probably around 4,500°C. Beyond the inner core is a layer of liquid rock, called the outer core, which extends about halfway to the surface. Beyond this is a thick layer of rock called the mantle, which is partly molten and runny. The thinnest layer, or crust, is on the Earth’s surface, floating on the red-hot liquid mantle. The crust is about 6 km thick under the oceans, but 30 to 40 km thick beneath the land. 

 

 

 

 

Why is the Earth like a magnet?

The Earth acts as if it is a huge magnet. When the solid rocky core moves inside the liquid rock above it, it creates a magnetic field with a north pole and a south pole. This field surrounds the Earth and extends right out into space. The Earth’s magnetic field is changing constantly. This means that the magnetic north pole is not always the same as the geographic, or true, North Pole that you find on a map, although it wanders about in the same region. Millions of years ago, the north magnetic pole lay in what is now the Sahara desert. 

 

 

 

 

How old is our Earth?

The Earth is thought to be about 4,600 million years old. The oldest rocks so far discovered are up to 3,800 million years old. The Universe is much older, and probably began about 15,000 million years ago. We can calculate the ages of the Earth and the Universe by examining meteorites, and also by looking at changes in the atomic structure of some of the elements found on the Earth. Radioactive elements decay at a steady rate, and these changes can indicate the age of the Earth and other planets, as well as the age of the stars. 

 

The Earth began over 4,600 million years ago. We believe that the Earth and other planets were formed from a flat gas cloud around the Sun. This cloud formed into small, cold particles which attracted one another, collided, and formed larger particles. This took place over a few million years. As the larger particles collided, they became hot, and melted. Iron from these formed the central core of the Earth, and other substances surrounded it.

The molten outer layer of the Earth cooled to form a thin shell. Sometimes molten rock escaped from under the surface in volcanic eruptions, as it still does today. Gases escaped from inside the Earth to form an ‘atmosphere’.

 

 

 

 

Structure of the Earth

The outer layer of the Earth is a thin, solid skin, called the ‘crust’. Below it is a region called the ‘mantle’? The outer layer of the mantle is made of molten rock, called ‘magma’. Below the mantle is a region of molten rock under great pressure. The central region of the Earth is a solid core.

Scientists predict that the temperature in the Earth’s core is about  6,000 degree C. They have studied temperature changes at different depths beneath the Earth’s surface and also believe that the melting point of iron – found near the Earth’s central core – is a good indication.

 

 

Continue reading "THE EARTH’S ORIGIN"

The oceans cover about two-thirds of the Earth’s surface and have existed for more than 3,000 million years!

The top layer of the ocean has a rich plant and animal life, the ‘plankton’. Millions of these minute organisms produce food for all the other sea animals. Plankton is one of the oldest forms of life on Earth. Deeper down at about a hundred metres, it is too dark for plants to grow, so the ocean bottom is mostly bare.

Winds blowing across the ocean cause waves. When winds blow over a great distance across the sea, they build waves which may be many metres tall.

 

 

 

The tides

Tides are caused by the pull of the Moon and the Sun on the waters of the Earth. When both the Sun and the Moon are in line with the Earth, their pulls add up, and the tides are very large. These are called ‘spring tides’. When the Sun and Moon are out of line with the Earth, their pulls oppose each other, and the tides are not so large. These are called ‘neap tides’.

 

 

 

 

Cannon Beach, Oregon, USA. The action of the waves can cause erosion of the coastline.

 

 

 

 

 

Papua New Guinea islands, Pacific Ocean – the seas make up two thirds of the Earth’s surface.

 

 

 

The Sun appears to us as if moves around the Earth. In fact, the Earth spins around on its axis like a top, one turn every day. The place where you live, points towards the Sun in the day, and away from it at night.

The Earth spins on its axis at a great speed: the surface of the Earth moves at more than 1,500 km/h. Gravity provides the force which stops us being thrown off the Earth. Gravity extends a long way from the Earth, and pulls anything within its range towards the Earth. The Moon and artificial satellites are held in orbit round the Earth by the pull of its gravity.

 

 

 

 

The seasons

The seasons are caused by the Earth’s orbit around the Sun. The diagram shows how the Earth’s axis is slanted. During summer in the northern world, the midday Sun is over a region north of the equator, so its rays are more concentrated and feel hotter. During winter, the Sun is over a region south of the equator, and the rays reaching the north spread out over a larger area. They are less concentrated, so they feel less hot. Places south of the equator have their summer when places north of the equator have winter.

 

 

 

 

 

Continue reading "SPINNING EARTH"

               We know that our Earth is ball-shaped. If we continue digging at a particular place, we would notice that the temperature goes on increasing with the increase in depth. Before we discuss the subject we must have an idea about the three main layers of Earth. The top, the second and the third. The top or first layer of Earth is a thin crust of hard rocks that floats on the second thicker layer of rock called “mantle”. This is so hot that most of its rocks are partly melted. The third layer is made of hot liquid iron. In fact, at the core it is extremely hot. The temperature can be imagined from the huge amount of energy which is released when the volcanoes erupt.

               Around the year 1800 some Italian scientists performed certain experiments, to make use of Earth’s internal heat. They dug a hole in the earth through which jets of hot steam and pungent gases shot out. These blow-holes are a sign of volcanic activity taking place under the ground. The gases they release into the air come from molten rocks known as magma which lies at depths ranging between 20,000 and 80,000 metres or more.

               Scientists found boric acid in these vents. An industry was set up to extract this chemical substance in Italy in 1818. Later it was discovered that the power of these gas jets could be harnessed for other tasks, including the generation of electricity. For the first time geothermal electricity was generated at Landarello in Italy in 1904.

               The internal heat can be used to produce electric power in four ways: dry steam, as at Landarello; hot water as at Reykjavik, in Iceland; low temperature areas in basins of sedimentary rocks, containing water between 40°C and 100°C which is used for agricultural purposes such as heating glass houses; and high pressure zones found by petroleum drilling deep in sedimentary basins. The natural gas released from the earth in particular localities (generally near deposits of mineral oil) is used as fuel and also as a source of energy.

               In the last few years the scientists have developed several mechanisms for the optimum use of Earth’s internal heat. They have been trying further to develop such instruments further that could be used to utilize the earth’s geothermal energy effectively.

 

 

 

What is the Diamond Ring effect?

Just before the Moon covers the Sun completely or just after the Moon uncovers the Sun during a total solar eclipse, a tiny portion of the Sun’s bright disc becomes visible on the Moon’s dark disc, giving an impression of a ring with a brilliant diamond on it.

 

 

 

 

 

What is node?

The Moon’s orbit is inclined at an angle of about 50 relative to the Earth. The monthly path of the Moon and the ecliptic are imagined to be two hoops hinged along a diameter and slightly displaced at an angle to each other, and then the hinges will represent the points of intersection known as nodes.

 

 

 

 

 

How does a lunar eclipse occur?

A lunar eclipse occurs when the Moon enters the shadow of the Earth and when the Earth comes between the Sun and the Moon. 

What is the relation between the phase of the Moon and a lunar eclipse?

When the Earth comes between the Sun and the Moon during a Full Moon, a lunar eclipse occurs if all the three bodies are in a line.

 

What causes a solar eclipse?

A solar eclipse occurs when the Moon comes between the Earth and the Sun, blocking the view of the Sun.

Can a solar eclipse be seen from all places on Earth?

No. the eclipse is actually a shadow transit where the Moon’s shadow crosses the surface of the Earth. Hence, only observers on Earth along the line of transit can see it.

How long can a solar eclipse last?

Not more than seven minutes and fifty eight seconds.

Why is solar eclipses comparatively rare?

Unless is a new Moon near the node, solar eclipses cannot occur. A solar eclipse occurs during a new Moon if the Sun, Moon and Earth are in line. It is, therefore, a rare phenomenon.

 

 

What are partial and total solar eclipses?

When the Moon partially covers the Sun it is partial solar eclipse. A total solar eclipse occurs when the Sun is completely covered by the Moon.

What is an annular solar eclipse?

Sometimes, the disc of the Moon appears smaller than that of the Sun in which case it is an annular eclipse, where the rim of the Sun’s disc remains visible around the dark disc of the Moon.

 

How does an annular eclipse occur?

The Sun and the Moon generally have the same apparent size in the sky. During a total solar eclipse, the Moon just covers the Sun completely. However, if there is an eclipse while the Moon is at apogee, then the apparent size of the Moon becomes slightly smaller, resulting in an annular solar eclipse.

How do partial and total eclipses occur?

A shadow of the Earth or the Moon consists of two regions- a dark central region called ‘umbra” and a less dark outer region around it called a “penumbra”. The eclipse will be total only if the observer in located in the zone of totality.

What is the maximum possible width of the zone of totality?

Since the Moon’s shadow just touches the Earth, the zone of totality is very narrow, having a maximum width of not more than 270 km approximately.

Can an observer in a supersonic aircraft follow the Moon’s shadow during a total solar eclipse so that it can be observed for a longer period?

It is possible to follow the Moon’s shadow in a supersonic aircraft during a total solar eclipse, thereby extending the observation period to about 40 minutes.

At what speed does the Moon’s shadow sweep across the Earth during a total solar eclipse?

About 2250 km per hour.

 

What are the Solstices?

During the year, the position of the Sun in the sky, as viewed from the Earth shifts from north to south and back again. In other words solstice occurs on either to the days on which the Sun is farthest north or south of the celestial equator each year. The points of solstice correspond to the northernmost and southernmost positions of the Sun in the sky.

 

 

 

What is the structure of the Earth?

Earth has a molten liquid core of iron, nickel and magnesium silicates. At the surface of the Earth is a solid layer called the crust. A semi fluid zone called the mantle exists between the crust and core. About 70% of the Earth’s surface includes north and south polar icecaps it is covered with water.

 

 

 

 

 

 

 

 

What is the precession of the Earth’s axis?

The Earth’s axis does not remain steady but wobbles like that of a tilted spinning top. This wobbling is called the precession of the Earth’s axis.

 

What causes the change in seasons on Earth?

In the northern hemisphere, the Earth’s 23.50 tilt towards and away from the Sun during June and January causes’ summer and winter respectively. It would be the converse in the converse in the southern hemisphere.

Does the change in the Earth-Sun distance during an year have any appreciable effect upon the seasons on Earth?

No.

 

 

Do the hemispheres have identical temperatures during summer and winter?

Theoretically, the Earth should have a slightly hotter climate in the southern hemisphere compared to the northern hemisphere. However, the larger mass of ocean in the southern since the ocean heats up and to even down more slowly than land areas.

 

 

 

Continue reading "The Earth"

Port Blair                           -41          

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