First Consequence: Extinction

Many researchers believe this oxygen increase resulted in the extinction of various anaerobic bacteria and archaea. Microorganisms that had thrived in oxygen-free environments could not survive in a world suddenly rich in oxygen. For these organisms, this era was not a Great Oxygenation Event but rather an Oxygen Catastrophe.

Second Consequence: The Onset of Ice

Things took a turn for the worse. The explanation lies in greenhouse gases. Today, these gases are often viewed negatively, but 2.4 billion years ago, they played a beneficial role. The Sun's output was only about 85% of what it is now, which made Earth inclined towards cooler temperatures. However, the greenhouse gases in the atmosphere prevented this cooling, keeping the planet warm.

Between 2.4 and 2.3 billion years ago, a transformation occurred. Newly generated oxygen reacted with atmospheric methane, converting it into carbon dioxide and water vapor. The water vapor precipitated as rain, while carbon dioxide was sequestered through natural processes, such as reacting with emerging landmasses. Consequently, the concentration of greenhouse gases in the atmosphere diminished, leading to a prolonged ice age lasting 300 million years.

Snowball Earth

This period, known as the Huronian or Makganyene Glaciation, marked the longest ice age recorded. Geological evidence from regions in Canada, the US, South Africa, India, and Australia supports this event. Before this glaciation, these rocks were part of the supercontinent Kenorland, which began to fragment, leading to increased bedrock erosion and greater absorption of carbon dioxide.

The exact scope of the glaciation is debated. Some propose that glaciers enveloped the entire planet, while others argue that this was not entirely the case. Regardless, it marked humanity's initial encounter with a devastating Snowball Earth.

How Did the Snowball Thaw?

So, how did the Huronian Glaciation conclude after 300 million years? The answer, as is often the case with global climate shifts, is: gradually at first, followed by a rapid change.

As ice accumulated, it removed liquid water from the Earth, causing sea levels to drop. Eventually, the lack of available water led to a halt in rain formation. Interestingly, some of the coldest regions on Earth, like Antarctica's McMurdo Valleys, are technically classified as deserts.

The thawing of the Huronian glaciation occurred simply because the planet ran out of rain. As sunlight warmed the ice, it began to melt, creating a feedback loop. The melting water absorbed solar heat, accelerating the thawing process. Bubbles of carbon dioxide trapped in the ice were released, warming the planet further, ultimately ending the ice age.

The Fragility of Our Atmosphere

It is astonishing how delicately balanced our atmosphere is. Any shift in this equilibrium can lead to catastrophic effects. Only someone foolish would dare to tamper with the Earth’s atmosphere.

This article is Part 24 in a series of 50 discussing Earth's history, chronicling 100-million-year segments. For more insights, check out Part 23: OXYGEN or Part 25: DNA. If you’re interested in the entire series, please consider following my work.