Evolution: Does oxygen level hold the key (Evolution)

by David Turell , Tuesday, November 03, 2015, 16:46 (3097 days ago) @ David Turell

Evolution was slow or non-existent for a billion years early on:, with very low oxygen levels:-https://www.sciencenews.org/article/new-fascination-earths-boring-billion-"Earth's long history starts with an epic preamble: A collision with a Mars-sized space rock rips into the young planet and jettisons debris that forms the moon. Over the next few billion years, plot twists abound. The oceans form. Life appears. Solar-powered microbes breathe oxygen into the air. Colossal environmental shifts reshape the planet's surface and drive the evolution of early life.-"After this wild youth of rapid change, things slowed down. About 1.8 billion years ago, the climate stabilized. Oxygen levels steadied. Evolution seemingly stalled. For around a billion years, not a lot changed on planet Earth. Scientists called this interval the dullest time in Earth's history. It came to be known as the “boring billion.”-***-
"The planet's first whiff of oxygen came more than 3.2 billion years ago, following the evolution of the earliest photosynthetic microbes, cyanobacteria (SN Online: 9/8/15). These bacteria churn out oxygen into the environment. When the microscopic critters die, however, their remains decay and consume oxygen. Normally the life and death of a cyanobacterium would result in no net oxygen gain. Luckily for oxygen-loving life, accumulating sediments can bury the decaying organic matter under the seafloor and halt the drawdown of oxygen.-"Before the boring billion, around 2.4 billion to 2.3 billion years ago, cyanobacteria flooded Earth's atmosphere with oxygen (SN: 10/10/09, p. 11). This oxygen rise, nicknamed the Great Oxidation Event, permanently altered the planet's chemical portfolio and purged the surface of nearly all oxygen-intolerant life.-"The breath of oxygen ultimately spurred the evolution of complex life-forms called eukaryotes, with distinct cell nuclei and organelles. Early eukaryotes — the forebears of animals and plants — appeared at the start of the boring billion, 1.8 billion years ago. During their first few hundred million years, single- and multicelled eukaryotes eked out a marginal existence while bacteria and archaea unequivocally ruled Earth's ecosystem."-Comment: no question oxygen is needed for today's complex animals, but much more than oxygen is required to advance evolution.