AP BIOLOGY

Detailed explanation-1: -One of the enduring marvels of life on Earth is that, by producing oxygen, the earliest organisms created conditions that enabled subsequent, more complex forms of life to thrive.

Detailed explanation-2: -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-3: -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-4: -Without the atmosphere, Earth would be lifeless. Carbon dioxide (CO2) and oxygen (O2) are the most important gases for living organisms.

Detailed explanation-5: -Oxygen played a key role in the evolution of complex organisms, according to new research published in BMC Evolutionary Biology. The study shows that the complexity of life forms increased earlier than was thought, and in parallel with the availability of oxygen as an energy source.