Category Earth Science

What is Earth?

Earth is our home. It is nearly 150 million km (94 million miles) from the Sun, and is the fifth largest planet in our solar system.  Its diameter is about 8,000 miles. And Earth is the third-closest planet to the sun. Its average distance from the sun is about 93 million miles. Only Mercury and Venus are closer.

Earth has been called the “Goldilocks planet.” In the story of “Goldilocks and the Three Bears,” a little girl named Goldilocks liked everything just right. Her porridge couldn’t be too hot or too cold. And her bed couldn’t be too hard or too soft. On Earth, everything is just right for life to exist. It’s warm, but not too warm. And it has water, but not too much water.

Earth is also the only planet in our solar system where water is found on the surface, which allows animals and plants to live there.

 

Picture Credit : Google

Is there life on other planets?

          Earth is perhaps the only planet in the solar system where life exists. This is because the conditions favourable for the existence of life are available only on the Earth. Conditions present in other planets make life almost impossible.

          Mercury is the planet closest to the Sun. It is difficult to see it even with a powerful telescope. It does not have any atmosphere. The temperature during the daytime may even go beyond 400°C. The lack of oxygen and the extreme temperature make life on Mercury impossible.

          Venus, which comes next in terms of closeness to the Sun, is often described as the sister planet of the Earth. Venus and the Earth are almost identical in size, mass and density. Its diameter is 0.95 times and mass is 0.815 times as compared to the mass and diameter of the Earth. It is surrounded by thick clouds of carbon dioxide (95%). The temperature on its surface is about 95 times more (480°C) than that on the Earth. This makes Venus the hottest planet in the solar system. Under these conditions life is not possible here.

           Mars comes after the Earth and is much colder than the Earth. Its average temperature is about – 62°C. At night it may drop to – 101°C. It has an atmosphere much thinner than that of the Earth. It has been found that it contains 1 to 2% argon, 2 to 3% nitrogen, 95% carbon dioxide and 0.3% oxygen. These conditions suggest the possibility of existence of life on it but so far no traces have been detected.

          All other planets beyond Mars (Jupiter, Saturn, Uranus, Neptune and Pluto) are farther away from the Sun. The surface temperature of these planets is so low that no living organism can survive there. Besides, their atmospheres contain gases like methane and ammonia which are not favourable to the evolution of living organisms.

          Thus our Earth is the only known planet in the solar system where life exists. 

Which planets have satellites?

          The heavenly bodies that revolve round the sun are called planets. There are nine planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. The bodies revolving round these planets are called their ‘satellites’ or ‘moons’.

          Scientific investigations made so far have revealed that all planets do not have satellites. For example, Mercury and Venus do not have any satellite. Earth has 1 satellite – the moon. Mars has 2 satellites and the Jupiter has 16. The number of the moons revolving round Saturn is 24. The Uranus and Neptune have 15 and 6 satellites respectively. Pluto has 1 satellite.

          The size of different satellites is different. There are some satellites which are bigger than moon. The diameter of two satellites of the Mars, Deimos and Phobos, and the outer satellites of the Jupiter, Ganymede and Callisto are as big as Mercury and Mars. The diameters of Titan and Triton – the satellites of Saturn and Neptune are 5150 kms and 2700 kms respectively and more than the diameter of our moon.

          Except Titan, all the satellites have small force of gravity. As such none of them has any atmosphere. Because of low temperature at Titan, it has an atmosphere consisting of methane and hydrogen. But there is no life on this satellite.

          As yet we have not come across any satisfactory theory regarding the origin of the satellites. However, it is believed that their origin is similar to that of our solar system.

How is the distance of stars from the earth measured?

          The stars which we see shining at night look very attractive and bright. Some stars look brighter than others. This is so because their sizes and distances from the earth are different. These stars are billions of miles away from our earth and shine with their own light. Do you know how the distance of stars form of earth is measured?

          Scientists have evolved a simple technique to measure the distance of the nearby stars. Suppose we want to measure the distance of a particular star ‘C’. We take its photograph from a place ‘A’ on the earth. After six months, the earth is at the position ‘B’, since it is revolving round the sun. We now take another photograph of the same star from the position ‘B’. A comparison of the two photographs will show that ‘AB’ is the diameter of the earth’s orbit round the sun and is equal to 186 million miles. Now the angle ‘ACB’ is measured. With the help of these two figures, the distance of the star ‘C’ is measured. This is known as the method of triangulation.

          Using this technique, the distance of many stars has been measured. The distance of Alpha Centauri from earth has been found to be about 4.35 light years. The distance of the Sirius has been determined to be 8.48 light years. However, this technique is not suitable for measuring the distance of very distant stars. The distance of such stars is determined on the basis of their brightness or colour. The most widely used system for measuring the distance of stars is the two-dimensional classification method developed by J.M.Johnson and W.W. Morgan. This system is based upon photoelectric measurement in three wavelength bands in ultra-violet, blue and yellow (or visual) regions of spectrum. This method is known as UBV system. Scientists have succeeded in measuring the distance of stars as far away as 8 million light years from the earth.

 

How are caves formed?

               Caves have for long been linked with the history of civilization in many interesting ways. In the stone age, men used to live in caves to protect themselves from cold and animals. Ancient people had many strange notions about caves. The people of Greece believed that their gods Zeus, Pan, Dionsus and Pluto lived in caves. The Romans believed that caves were the homes of nymphs and sibyls. People of Persia worshipped caves considering them to be the abodes of God. Today, huge and beautiful caves all over the world have become centres of attraction for the tourists. Do you know how these caves were formed?

               A cave is a deep hollow space in a mountain. It is formed in different ways. When water waves coming from the sea, collide with the mountains, they wash away the soft stones present in between the layers of the rocks. This process continued over a period of thousands of years and created large spaces inside the mountains which we call caves.

               Some caves are found below the Earth’s surface also. These have been formed by the water streams flowing below the Earth’s surface. The underground water streams wash away the lime-stone from the rocks and the voids so created are called caves.

               Quite often, waterfalls create hollow spaces within the rocks which ultimately become caves. Such caves have been formed below the Niagara Falls.

               Caves are also formed by the volcanic changes taking place in the earth’s layers. Some caves are very long while some are very deep. The deepest cave is ‘Guffre de la piere st.’ situated on the border of France and Spain. It is 1310 metres (4300 ft) deep. The longest cave, ‘Flit Ridge cave system’ is situated in America and is 116.8 km (73 miles) long.

               The longest single cavern in the world is the Sarawak chamber in Eastern Malaysia. It is 700 metres long and was discovered in 1980. Mammoth Cave National Park in the US State of Kentucky is the largest cave system of the world about 307 km long. In India, caves of Ajanta and Ellora are famous for their beautiful sculptures. 

How are Volcanoes formed?

            A volcano is a mountain having an opening on the surface of the Earth from which fire, smoke and ashes come out continuously. Mountains of this type are created by upheavals inside the Earth.

            The formation of volcanoes can be understood as follows. Temperature inside the Earth goes on increasing as we go into the interior of the Earth. At a depth of approximately 30 km, the temperature is so high that it can melt rocks. When rocks inside the Earth get melted, they start expanding. These molten rocks are known as magma. In some parts of the Earth, this magma starts coming up through openings in the Earth’s crust. When the pressure exerted by this magma is considerably high and the Earth’s crust at some places is weak, the crust breaks at those places and, as a result, hot gases, liquid and solid material of the red molten rocks start coming out. This is called volcanic eruption. The ejected hot smoke, ashes and stone pieces constitute what we call lava. This lava goes on solidifying in the shape of a cone and, on cooling; it takes the form of a mountain on the surface of the Earth.

            Fire and smoke keep on flowing out of the opening of the volcano until the molten material inside the Earth is exhausted. Such volcanoes from which lava stops coming are called dead volcanoes. There are more than 450 volcanoes in the world. The number of volcanoes in Indonesia is quite large. The highest dead volcano of the world is in Argentina; it is 6,960 metres high. One of the most violent volcanic eruptions was on the island of Krakatau, near Sumatra in 1883 which produced tidal waves in the oceans throughout the world.