Scientists infer that oxygen in Earths atmospheredid not exist in large quantities until after

EARTH SCIENCE

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Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]

Scientists infer that oxygen in Earth’s atmospheredid not exist in large quantities until after

A	the first multicellular, soft-bodied marineorganisms appeared on Earth
B	the initial opening of the Atlantic Ocean
C	the first sexually reproducing organismsappeared on Earth
D	photosynthetic cyanobacteria evolved inEarth’s oceans

Explanation:

Detailed explanation-1: -Scientists infer that oxygen was absent from the early atmosphere on Earth due to traces in the fossil record, where the chemical composition of the rock layer in the rock strata is analyzed, which showed an anoxic environment.

Detailed explanation-2: -Cyanobacteria are photosynthetic. They convert sunlight into energy and produce oxygen as a waste product. Back then, the Earth’s atmosphere didn’t have free oxygen in it as it does today. It was locked up in water molecules, or bonded to iron in minerals.

Detailed explanation-3: -The release of oxygen by cyanobacteria was thus responsible for changes in the earth’s atmospheric composition, the rise of aerobic metabolism and, ultimately, the evolution of multicellularity. Oxygen is the primary molecule that makes Earth what it is today, far more hospitable and beautiful than the early earth.

Detailed explanation-4: -The result is that lab-grown cyanobacteria will produce oxygen but to no more than 10% of our present levels-exactly the amount of oxygen produced in the Proterozoic.

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