One likely reason that only microbes existed for the first two billion years of life is...

One likely reason that only microbes existed for the first two billion years of life is

a) high concentrations of ozone in the stratosphere.

b) the absence of nitrogen in the environment at the time.

c) the toxicity of oxygen to multicellular organisms.

d) high levels of iron oxide in the water.

e) low concentrations of O2 at that time.

Expert Solution

Ans:

Around 3.5 billion years back, microbial mats represented the first form of life on earth.These were multilayered films of prokaryotes,mainly consisting of bacteria along with some archae.They mostly thrived on moist surfaces and each of the prokaryotic cell they were made up of, carried out metabolic pathways of their own type. Their main source of energy where the chemical energy found near the fissure's in the earth's surfce which releases heated H2O.

The nature of atmoshphere that prevailed during first 2 billion years of earth was anoxic.That is the atmoshpere lacked molecular oxygen.Hence, those organisms who were anaerobic and do not require oxygen for their metabolism could only grow during that period of earth's life.

Later, phototrophic organisms came into existence, as they could convert the solar energy into chemical energy and then these phototrophic organisms evolved into cyanobacteria which began to oxygenate the atmosphere.

Hence, the answer is (e) low concentrations of O2 at that time.

gladiator answered 1 year ago

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