AP BIOLOGY

Detailed explanation-1: -Oxygen played a key role in the evolution of complex organisms, according to new research published in BMC Evolutionary Biology.

Detailed explanation-2: -Four billion years ago, Earth’s atmosphere had little or no free oxygen. That changed when bacteria evolved the ability to photosynthesize, which releases oxygen as a byproduct. For example, the first jump in Earth’s oxygen levels may have been triggered by the proliferation of photosynthetic bacteria in the oceans.

Detailed explanation-3: -The finding could change ideas of how and when complex life evolved on Earth, and how likely it is that it could evolve on other planets. Oxygen in the Earth’s atmosphere is necessary for complex forms of life, which use it during aerobic respiration to make energy.

Detailed explanation-4: -This makes oxygen the most important element for origin of life because its presence in present day oxidizing atmosphere does not allow the origin of life as it occurred in primitive reducing atmosphere.

Detailed explanation-5: -Eukaryotes arose about 1.6 billion years ago, at a time when oxygen levels were still very low on Earth, both in the atmosphere and in the ocean.