One day oxygen destroyed almost all life on Earth: how and when it happened

 During an event known as the Oxygen Disaster, the Earth froze and almost all living organisms on the planet became extinct.

Although life emerged early in Earth's history, it was only about 2.7 billion years ago that cyanobacteria, an early photosynthetic organism, began to produce oxygen abundantly. Oxygen gradually began to accumulate in the atmosphere over hundreds of millions of years until it suddenly caused the Earth to turn into a huge snowball. For about 300 million years, the Earth remained frozen, but the few living organisms that survived continued to struggle for survival, writes Big Think.

Planet Earth was formed more than 4.5 billion years ago, and life first appeared on it just a few hundred million years later. But no event brought the end of life on Earth closer than the Oxygen Catastrophe. The slow alteration of the Earth's atmosphere by the gradual addition of oxygen proved fatal to the most common types of organisms then existing on the planet. For several hundred million years, the ice age continued on Earth, when the planet turned into a huge snowball. This catastrophe almost completely put an end to life on Earth.

First life on Earth

With virtually no competitors or predators and virtually unlimited resources, the living population of organisms will initially grow exponentially. With each successive generation of organisms, levels of resource consumption increase, metabolic products continue to increase in quantity and concentration, and the overall population of organisms continues to grow and grow. As long as resources are available and the environment remains non-toxic to the population of organisms, this process will continue.

But there is always a limit, since in any environment there is always a finite amount of resources. At some point, the metabolic processes that these organisms use to manage their life functions will produce enough waste that it reaches a critical level. Ultimately, an environment is created that is toxic to the organism's population.

In the earliest stages of Earth's development, a simple form of life arose: single-celled organisms. There is clear evidence for the existence of single-celled bacteria during the first billion years of Earth's history.

One of the hallmarks of biological evolution is that life will mutate and evolve to fill every available ecological niche. From these earliest life forms emerged archaea capable of surviving in the deep sea around hydrothermal vents. Hundreds of millions of years after the earliest organisms arose, the first fully photosynthetic organisms appeared.

A class of organisms has emerged that use water for photosynthesis – cyanobacteria. Unlike other organisms, cyanobacteria produce molecular oxygen as a byproduct. Cyanobacteria became particularly abundant approximately 2 billion years after the formation of the Earth.

Too much oxygen

Somewhere between 2.5 and 3.0 billion years ago, too much free oxygen accumulated in the Earth's atmosphere. Slowly but surely, oxygen levels began to rise, and organisms with a seemingly unlimited resource, that is, sunlight, began to thrive and multiply, and add waste to the environment, particularly oxygen.

Large-scale ice age

The Sun's energy output was much lower and so the large amount of atmospheric methane was the only thing that kept the Earth warm enough to support liquid water on its surface. As oxygen destroyed the greenhouse gas, the planet could not stay warm. This gave rise to an ice age that lasted approximately 300 million years.

No matter how catastrophic this was for most organisms living on Earth at that time, the chain of life did not break at that moment. Despite the toxic environment, cyanobacteria continued to thrive in at least some environments on Earth. Meanwhile, the populations of the other few surviving organisms evolved in different directions. This led to the emergence of more complex organisms that had a chance to survive.

After the end of the Ice Age, the first eukaryotic cells appeared on Earth. They later gave rise to all living plants, fungi and animals. Some scientists believe that humanity would never have arisen if oxygen had not destroyed the methane-rich atmosphere and given life the opportunity to develop in a new direction. It is estimated that 2.5 billion years ago the Earth experienced the largest mass extinction in its history.