Origin of Earth & Early Atmosphere — NEET Biology
📚 Practice ConceptHuge clusters of galaxies comprise the universe. Galaxies contain stars and clouds of gas and dust. Considering the size of universe, earth is indeed a speck. The Big Bang theory attempts to explain to us the origin of universe. It talks of a singular huge explosion unimaginable in physical terms. The universe expanded and hence, the temperature came down. Hydrogen and Helium formed sometime later. The gases condensed under gravitation and formed the galaxies of the present day universe. In the solar system of the milky way galaxy, earth was supposed to have been formed about 4.5 billion years back. There was no atmosphere on early earth. Water vapour, methane, carbondioxide and ammonia released from molten mass covered the surface. The UV rays from the sun brokeup water into Hydrogen and Oxygen and the lighter H2 escaped. Oxygen combined with ammonia and methane to form water, CO2 and others. The ozone layer was formed. As it cooled, the water vapor fell as rain, to fill all the depressions and form oceans. Life appeared 500 million years after the formation of earth, i.e., almost four billion years back.
Which of the following statements regarding the oxygenation of Earth’s early atmosphere and primitive life forms are NOT correct? S1: Early Earth's atmosphere was largely reducing, containing gases like methane, ammonia, and water vapor but lacking free oxygen. S2: The earliest forms of life were most likely single-celled, non-photosynthetic organisms that thrived in a water environment. S3: Cyanobacteria were among the first organisms to perform oxygenic photosynthesis, leading to the accumulation of free oxygen in the atmosphere. S4: The released oxygen immediately formed the ozone layer, which then facilitated the direct origin of the first cellular forms on land. S5: The initial rise in atmospheric oxygen caused by photosynthetic life forms led to a significant decrease in temperature, allowing water vapor to condense into oceans.
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