Evolution -Introduction | Our Solar System | Big - bang Theory

What is Life ?

Life is an inherent capacity that an organism possesses to maintain and reproduce itself. Philoso phers have different views about life. Here, we study the biological aspects of life.

Events in the History of Life

The history of life comprises two events — first, the origin of life and second, the evolution of life (the mechanism involved in the changes of living organ isms through time). Let us first know how were the universe and earth originated ?

Origin of Universe

There are several theories regarding the origin of universe but the most accepted theory is big - bang theory.

Big - bang Theory

This theory was proposed by Abbe Lemaitre in 1931. According to big - bang theory about 15 billion years ago, cosmic matter was in a condensed form. A fiery explosion tooke place which broke the condensed matter and scattered its fragments into space at an enormous velocity making a

" big bang " sound and thus the theory came to be known as big bang theory . Immediately after the explosion , the universe (L. universum - whole world) or the cosmosa (Gk . Kosmos - world) expanded rapidly from a size of a pin to about 2,000 times the size of the sun.

In 1925, Edwin P. Hubble pointed out that the univese actually consisted of millions of galaxies. He also pointed out that the universe is in a state of rapid expansion.

Our Solar System

Nebular Hypothesis is one of the most popular hypotheses to explain the origin of solar system. Nebular hypothesis was first proposed by Kant in 1755. Laplace revised it in 1796 . According to this hypothesis our solar system was probably created about 4.5 to 5 billion years ago when the gaseous cloud called solar nebula was formed. As the cloud condensed the central mass formed the sun and the peripheral celestial bodies (bodies in the sky) form planets, satellites, asteroids, meteors and comets forming the solar system. Thus the sun along with its peripheral celestial bodies comprise the solar system.

The solar system comprises the sun , eight planets and their satellites (moons), asteriods , comets , meteors and meteorites.

The Sun. The sun was formed about 4.6 billion years ago. The sun is one of the stars and nearest to earth. The sun is the ultimate source of heat and light. The hottest place in the solar system is the centre (core) of the sun.

Galaxies. A galaxy is a large system of stars, dust and gas held together by gravity. Milky Way or Akash Ganga visible in the sky during night is a galaxy. Solar system is located in this galaxy.

Planets. There are eight planets which were formed about 4.6 billion years ago in our solar system. They are Mercury. Venus, Earth, Mars , Jupiter, Saturn, Uranus and Neptune. An easy way to remember the names of the planets "My Very Efficient Mother Just Served Us Nuts". Till August 2006 , Pluto was also considered a planet but it was disqualified and now may be called " Dwarf Planet ".

All the planets are grouped into two classes:

1. Inner Planets. They have rocky surface. They are warm to hot and include Mer cury , Venus . Earth and Mars.
2. Outer Planets . They are gaseous, cold and giant and include Jupiter, Saturn , Uranus and Neptune.

Satellites or Moons The satellites or moons are the small bodies that revolve round their mother planets in the solar system. The satellites or moons are as follows- earth has 1, Mars 2, Jupiter 67, Saturn 53, Uranus 27, Neptune 13, Mercury and Venus do not have any satellite or Moon. Asteriods.

Asteriods are small rocky bodies that move around the sun mostly between Mars and Jupiter.

Comets. Comets are small icy bodies that orbit around the sun. They often develop a long tail. A comet has two distinct parts- a head and a tail. The tail of the comet always points away from the sun.

Meteors. They are tiny particles of dust left over from comets which produce streaks of light as they enter the Earth's atmosphere with great speed and burn out.

Meteorites ( Chunks of iron and stone ). They are stony or metallic objects that have fallen to the earth from outer space. These are often fragments of asteroids. Study of origin of universe is called cosmogony while the study of universe is known as cosmology.

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MANISH MEVADA

M.Sc, M.Phil, B.Ed

GUJARAT BIOLOGY NEET

NEET MATERIAL IN GUJARATI 

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