Question

The atmosphere of early earth probably contained no oxygen until the emergence of organisms that:
A. Were chemoautotrophic.
B. Were oxygen-respiring.
C. Used hydrogen sulfide as a hydrogen source for photosynthesis.
D. Used water as a hydrogen source for photosynthesis.

Answer 1

Hint: Earth's original atmosphere was abundant in ammonia, methane, water vapour, and the noble gas neon, but it lacks free oxygen. It is possible that hundreds of millions of years split up the first biological production of oxygen by single-cell organisms and its subsequent accumulation in the atmosphere.
Complete Step-by-step answer:

During the Archean Eon, methane droplets in the air wrapped the young Earth in a global haze. There was no oxygen gas on Earth. Oxygen was only present in components like water. Complex chemical reactions in the young oceans converted carbon-containing molecules into simple, living cells that did not require oxygen to live. Instead, they made energy out of sulfur and other components. 2.7 billion years ago, bluish-green microscopic organisms known as cyanobacteria flourished in World's oceans. They made gaseous, or free, oxygen from water, carbon dioxide, and sunlight, and the process is known as photosynthesis.
As cyanobacteria have generated more free oxygen, the amount of oxygen in the atmosphere has attained one per cent of today’s level, which is 21 per cent. After photosynthetic bacteria was making oxygen for approximately 300 million years, sufficient oxygen built up in the atmosphere to oxidise (mix with) the iron in rocks and soil in order to create reddish iron oxide and make huge expanses of redbeds.
Therefore the correct answer is Option D.
Note: Three billion years ago, the sun was only around 70 per cent as bright as it is today. Earth would have had to be frozen over, but it did not. Greenhouse gases in the atmosphere, primarily carbon dioxide and methane, trap enough of the sun’s heat to maintain temperatures above zero.