UTS Voice
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What is life? It is very difficult to answer. Life is generally defined philosophically as well as biologically. Before defining life we need to answer the question of origin of life? There are two lines of thinking about the way life first emerged. If life arose from a biotic process, then it must exist everywhere, wherever chemicals and biological evolution can lead to conditions that are suitable. Origin of life should be an inevitable consequence of laws of physics as inherent in the Schrodinger’s equation. With about 200 billion stars in our galaxy and over 100 billion galaxies in the universe, we must have a large number of hospitable planets on which life could exist, as can be predicted by probability considerations given by the Drake Equation.’
As on earth, it is reasonable to assume that life elsewhere must also be carbon and water based, although other possibilities like silicon- based structures have been discussed. If life exists anywhere else, it is unlikely to have shapes and forms similar to ours. So if we wish to look for life, we ought to define what exactly is meant by life. In brief, life must satisfy the conditions of reproduction and metabolic activity and be capable of change through these processes.
On the other hand, all experiments done hitherto on the Earth show life can only arise from life, Chemists have been able to make complex organic molecules such as proteins, amino acids, DNA, RNA and other complex building blocks of life in the laboratory but no one has been able to synthesize a cell or put together simple structures such as mitochondria or chloroplasts from its constituents. Abiotic synthesis of a cell may, therefore, be the key to the origin of life. Whether life exists elsewhere or not would be determined by the probability of the formation of the first cell from end products of chemical evolution, which clearly must have occurred in many parts of the universe.
Different theories have been propounded to explain the facts about life. One of the most acceptable theory is of Oparin- Haldane Theory which is similar to the modern theory of origin of life. This theory caters both chemical and biological evolution.
Summary of main steps in the origin of life according to Modern theory of Origin of Life.
There other theories which presents and gives several fact about the origin of life.
First of all we know from fossils found in deep sea sediment cores that, over the aeons, life have evolved from simple to complex forms. Fossils records on the earth show that life started at about 3.5 billion years ago or even a few hundred million years earlier and the complexity has grown exponentially with time. Secondly, life occurs wherever conditions are favourable for its sustenance. Life has been found in diverse environments like Antarctica and in hydrothermal vents at the bottom of the oceans, where photosynthesis is not possible, due to lack of sunlight. Here, other alternatives path ways such as fixation sulphide, the number of species grows exponentially. Thus starting with single bacteria, a colony as big as the whole earth can grow in a period as short as week. We may therefore infer that, wherever life is found, it will be in abundance.
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