Alexander L Oparin (1894•1980), a Russian biochemist, and J. B. S. Haldane (1892-1964), a British scientist, put forward the concept that the first living thing evolved from non-living things. They also suggested what the sequence of events might have been. In 1923, Oparin postulated that life originated on Earth at some point of time in the remote past and under the conclusions no longer observed. In his book, The Origin of Life (1938). Oparin submitted that abiogenesis first, but biogenesis ever since, Oparin’s theory Is known as primary abiogenesis.
According to Oparin and Haldane (1929).spontaneous generation of early molecules might have taken place if the Earth once had more reducing atmosphere compared to the present oxtd1sLng atmosphere. Moreover. transformation of those lifeless chemicals in to living matter extended over some one billion years. Oparin and Haldane agreed that the primeval Earth contained little. If at all, oxygen. Perhaps. in the primitive atmosphere oxygen in the free gaseous state was virtually absent. However. oxygen remained bound in water and metallic oxides on the surface of rocks and its particles. Geological record shows the presence of such reduced materials like urinate, pyrite, etc. In the sediments, Implying that the conditions then were strongly reducing (non oxygenic). Therefore. no degradation of any organic compound arising in the primeval Earth could have taken place. As there was no ozone layer in the atmosphere any absorption of UV radiations that Is lethal to our present lives was possible In the primordial Earth. The early gas cloud was rich In hydrogen. being present in the form of methane, ammonia, and water (H2O). Thus. Carbon, nitrogen and oxygen were available In the form of their saturated compounds. Moreover. the atmospheric water vapor condensed Into drops of water and fell as rain that rolled down the rock surfaces and accumulated to form liquid pools and oceans. In the process, erosion of rocks and washing of minerals into the oceans were inevitable. Thus. Haldane’s hot dilute soup was produced. And the stage was set for combination of various chemical elements.
Atmospheric chemicals and those in water produced small precursor molecules. like amino acids. sugars, nitrogenous bases etc, These precursor molecules then combined resulting In the appearance of proteins, polysaccharides and nucleic acids. The energy sources for such reactions of organic synthesis were the UV radiations (solar radiation), electrical discharges (lightning). Intense city heat (volcanic eruption) and radioactive decay of various elements on the Earth’s surface. Once formed. the organic molecules accumulated In water because their degradation was extremely slow In the absence of any life or enzyme catalysts (F1g. 3.31. Such transformation is not possible in the present oxidising atmosphere because oxygen or microorganisms will decompose or destroy the Having particle that may arise by mere chance.

ORIGIN OF LIFE:

The oldest surviving terrestrial rocks, about 4.3 billion years old, contain no definite trace of life. At least not recognizable as yet. Some rocks, about 3.9 billion years old: contain carbonates. Geologists interpret that these carbonates have resulted from life processes. Therefore, life was present on Earth about 3.9 billion years ago. However. the oldest micro fossils discovered so far are that of photosynthetic cyanobacteria that appeared 3.3 to 3.5 billion years ago. Given this background, we can only speculate how life has originated and when.

Theories on the Orlgin of Life:

Many theories have been advanced to explain the origin of life. Most of the ideas on the origin of life fall into one of our categories.

(i) Special Creation: This idea embodies that life on Earth is a special or divine creation of one or more superior, intelligent, and all-powerful being, the God. It also attributes the origin on Life to a supernatural or vitalistic event, at a particular time in the past. It upholds that life is immutable and has not changed ever since its. origin.

(ii) Spontaneous Generation: According to this theory, life originates spontaneously from lifeless matter abeogenesis for example, frogs could arise from moist soil. However, this idea had been put to rest when Louis Pasteur (1862) provided proof that micro-organisms come only from other micro-organisms. Since then, it is being widely accepted that life originates from pre-existing life- Biogenesis.

(iii) Extraterrestrial or Cosmic Origin: This idea holds that life is coeternal with matter without any beginning. This notion advocates that life could have originated once or several times in various parts of the Galaxy in the Universe. The alternative name of this cosmozoan theory is panspermia. which holds that ’spores’ or ’see s (sperm) having extraterrestrial origin might have infected the barren Earth at the time of its origin or afterwards. Likelihood of this notion is remote because the hazards known to exist in the interplanetary space are not conducive to life. These non-conducive conditions are extremely low temperatures. Lack of atmosphere, utter dryness and very high flux of cosmic and ultraviolet radiation from the sun.

(iv) Terrestrial orAbiogenic Origin :This idea holds that life arose by a series of sequential chemical reactions. There is a general consensus of scientific opinions that life originated on Earth from collections of organic molecules that were produced early in the history of Earth.