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It took 200 million years for Earth to get its oxygen

Oxygen is the lifeblood of our planet, the invisible element we breathe every moment. But Earth wasn’t always this welcoming to complex life. In fact, it underwent a dramatic transformation over 200 million years to become the oxygen-rich world we know today.

The Great Oxidation Event (GOE) is often touted as a pivotal moment in Earth’s history, but new research suggests it was less of an “event” and more like a geological epic.

Earth’s oxygen secrets in ancient shales

University of Utah geochemist Chadlin Ostrander and his international team have been digging into this ancient story.

Their focus: marine shales from South Africa’s Transvaal Supergroup, which are essentially time capsules from billions of years ago. These shales hold clues to the oxygen levels in Earth’s early oceans, a piece of the puzzle that’s been missing until now.

“We really don’t know what was going on in the oceans, where Earth’s earliest lifeforms likely originated and evolved,” explained Ostrander. “So knowing the O2 content of the oceans and how that evolved with time is probably more important for early life than the atmosphere.”

Thallium isotopes

To unlock these secrets, the researchers turned to a rather unusual tool: thallium isotopes.

By analyzing the ratios of thallium isotopes in the ancient shales, the team was able to track the rise and fall of oxygen in the oceans.

“Emerging data suggest that the initial rise of O2 in Earth’s atmosphere was dynamic, unfolding in fits-and-starts until perhaps 2.2. billion years ago,” said Ostrander. “Our data validate this hypothesis, even going one step further by extending these dynamics to the ocean.”

Fluctuations in Earth’s oxygen levels

The results were astounding. They revealed a striking correlation between the fluctuations in oxygen levels in the ancient oceans and those in the atmosphere.

This correlation, previously identified through sulfur isotope analysis, was further confirmed by the presence or absence of oxygen indicators in the marine shales.

When signs of oxygen were found in the shale samples, indicating periods of oxygenation in the oceans, the researchers also found evidence of atmospheric oxygenation during the same periods. Conversely, when atmospheric oxygen levels decreased, so did the oxygen levels in the oceans.

This remarkable synchronicity suggests a complex and interconnected relationship between the Earth’s atmosphere and oceans during the oxygenation process. It implies that both systems played a vital role in the gradual accumulation of oxygen on our planet, with changes in one influencing the other.

Earth’s rocky road to oxygenation

So, why did this process take so long? Early Earth was a hostile environment. While cyanobacteria were diligently producing oxygen through photosynthesis, other geological and chemical processes were working just as hard to consume it.

Volcanic eruptions spewed out oxygen-hungry gases, and minerals readily reacted with any available oxygen.

“Earth wasn’t ready to be oxygenated when oxygen starts to be produced. Earth needed time to evolve biologically, geologically and chemically to be conducive to oxygenation,” explained Ostrander.

It was only after hundreds of millions of years of this back-and-forth that the scales finally tipped in favor of oxygen.

GOE’s lasting impact

The Great Oxidation Event marked a significant turning point in the history of life on Earth. The increased availability of oxygen in the ocean and atmosphere revolutionized the way organisms produced energy.

Aerobic respiration, a process that utilizes oxygen to break down nutrients and generate energy, became possible. This allowed for the evolution of larger, more complex lifeforms, as aerobic respiration is far more efficient than anaerobic alternatives.

The GOE set the stage for the incredible diversity of life we see today. From ancient trilobites to the mighty dinosaurs, and ultimately to humans, the rise of oxygen has been instrumental in shaping the course of evolution.

Ostrander’s research not only provides insights into this pivotal event but also serves as a reminder of Earth’s extraordinary ability to adapt and transform over vast timescales.

The next time you inhale, consider the incredible journey oxygen has taken to reach you – a journey spanning billions of years. It’s a journey that has fundamentally shaped the world we live in, and one that continues to influence the evolution of life on our planet.

The study is published in the journal Nature.


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