An Event That Changed Billions of Years of Earth’s History Imagine if you stopped receiving oxygen; within seconds, your brain would stop functioning, and within a few minutes, the brain would be severely damaged, leading to death. Now imagine a world without oxygen; obviously, there would be no complex life, including reptiles, birds, mammals, flowering plants, and humans, and the oceans might appear reddish-brown due to the presence of unoxidized iron; the landscape of Earth might almost look like present-day Mars. The ultraviolet rays from the Sun would directly hit the Earth due to the absence of the ozone layer. In one sentence, there would be no aerobic life; only microorganisms that can survive without oxygen would exist. Your imagination was real; billions of years ago, Earth used to be like this. In 1927, a geologist named A. M. MacGregor was studying very old rocks [1] in present-day Zimbabwe. Inside one of these rocks, he found small, smooth, rounded pieces of a golden-color...