Life is the power that an organism possesses to maintain and reproduce itself. The origin of life has been which form the life originated on this earth? There are several diverse views regarding the origin of the earth, and indeed the universe.

ORIGIN AND EVOLUTION OF LIFE

A Research Done By Dr. Aditya Dadhich.

ORIGIN OF UNIVERSE SOLAR SYSTEM 

It is believed that the Cosmos, which comprises all the material of reality, originated 10-20 billion years ago. The prevalent view is that Cosmos originated with a massive explosion of tightly condensed matter billions of years ago the big bang theory. The matter exploded throwing out hydrogen atoms and related nuclei which became organised into galaxies.

Cosmologists have estimated that there are approximately 100,000 million galaxies. All galaxies are moving away from one another at a great speed, approaching the speed of light. Our galaxy, the Milky Way, is just one of these galaxies (Fig. 1). All stars that we can see with the naked eye belong to our galaxy. The Sun is a medium-sized star lying about two-thirds of the way from the centre of the Milky Way. The Sun and its planetary satellites make up the solar system.

Our solar system probably arose as a swirling cloud of gases (called nebula) that eventually condensed into the Sun and the planets. The early earth also arose as a mass of gases but shortly afterward a core of heavy metals like nickel, copper, iron and lead formed. Overlying this core is a relatively thick mantle (shell) covered with a thin crust forming the surface of the earth. One of the theories regarding the origin of earth upholds that it was originally a cold mass that heated up under forces of compression in the settling and synthesis of core materials. Radioactivity also produced a great deal of heat. After about 750 million years the earth cooled and the present crust forming the surface developed. Today we are living on a relatively cool earth.

Of all the planets of the solar system, the earth is the only planet on which life as we know has evolved. What makes the earth so special a place in the solar system or perhaps in the whole universe? The earth has a special relationship with the Sun. Life on the earth would not have survived, but for the Sun. The Sun is steady source of energy for all basic processes that sustain life. The planet Mercury is close to the Sun and therefore exposed to the brunt of its burning nearness. Even on the Venus that lies between the Mercury and Earth, the heat is so intense as to completely evaporate all water that might have been present.

 Moreover, high levels of carbon dioxide in turn lead to further heating of the planet owing to greenhouse effect. Indeed, Venus is too hot to support even primitive forms of life. Earth, on the other hand, is just at the right distance from the Sun to retain water. This water absorbs the excess carbon dioxide and returns it to the earth in the form of carbonate rocks. The presence of water on the earth helped primitive marine forms of life to emerge and survive. These organisms further cleansed the earth's atmosphere of excess CO2 through photosynthesis. This in turn lead to the rise of oxygen level in our atmosphere and evolution of higher forms of life. In our solar system, Mars has also provided evidence of possibility of life, since it had earlier a moderate climate and enough surface water. But being a small planet, with a smaller gravitational field, it could not hold on to its CO2. The solar energy which is trapped by the gas could, therefore, no longer be retained.

ORIGIN OF LIFE

The origin of life is one of the great mysteries in the Universe.  To determine the origin of life, scientists are investigating the problem in several different ways.  Some scientists are studying life on our own planet. Some scientists are seeking out life or fossil life on other planets or moons in our solar system.  And other scientists are trying to detect life in other solar systems, either by measuring life's effects on the atmospheres of distant planets or by measuring artificial radiation like radio signals that may be produced by advanced life.

    Thus far, the most fruitful approach has been to examine life on our own planet.  However, even in our own backyard, it is difficult to determine life's origins because it began at least 3.5 billion years ago.  We know that life began at least 3.5 billion years ago, because that is the age of the oldest rocks with fossil evidence of life on earth.  These rocks are rare because subsequent geologic processes have reshaped the surface of our planet, often destroying older rocks while making new ones.  Nonetheless, 3.5 billion year old rocks with fossils can be found in Africa and Australia.  They are usually a mix of solidified volcanic lavas and sedimentary cherts.  The fossils occur in sedimentary cherts.

Above left is of about 3.5 billion year old lava.             

Above Right is about 3.5 billion year old sedimentary chert.

    Chemical traces of life have also been detected in slightly older rocks.  In Greenland, a series of ancient metamorphosed sediments have been found.  Analyses indicate the sediments were deposited about 3.8 billion years ago.  They also revealed carbon isotope signatures that appear to have been produced by organisms that lived when the sediments were deposited.

    In all cases, life as we understand it must have water.  This general rule is true on Earth and is thought to be true elsewhere in the solar system.  Currently, life is being sought on Mars where water may have once flowed on the surface and Europa where a subterranean sea of water may exist beneath its icy surface.

    If one analyzes the genetic information in a variety of modern organisms living on Earth, one can begin to group and separate organisms based on their common (or disparate) properties.  This type of analyses is intuitive at some levels.  For example, most people recognize that mule deer and white tail deer are more closely related than mule deer and grizzly bears.  Consequently, in a tree of life, mule deer would appear closer to white tail deer than grizzly bears.  This same process can be applied to all organisms and has led to three large domains of life: Bacteria, Archaea, and Eukarya.  Humans, as well as other complex mammals, are part of the Eukarya group.  If one traces the genetic information in organisms in all three groups, it appears they have a common ancestor or at least ancestors that share a common set of traits.  In either case, it appears the earlist form of life in the tree of life were thermophilic or hyperthermophilic organism, which means they lived in systems composed of hot water.

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