Life on Earth has not always transformed the planet as we see it today. More than 3 billion years ago there already existed organisms capable of producing oxygen, but the atmosphere remained almost without that gas for about billions of years. Recent researches explain why this happened and show how elements like nickel and urea stopped this process.
Understanding this also helps scientists look for life on other planets, so let’s learn more about this process.
Life on Earth
Today, oxygen is essential for most living beings. Without it, human beings, animals, and many microorganisms wouldn’t survive. However, at the beginning of Earth’s history, the atmosphere was very different: Cyanobacteria, tiny microorganisms that produce oxygen through photosynthesis, existed at least 2.9 billion years ago. Despite their presence, oxygen didn’t accumulate in the air right away.
This period before the Great Oxidation Event, which happened between 2.4 and 2.1 billion years ago, lasted almost 500 million years! During this time, oxygen was produced, but it was immediately consumed or trapped by chemical reactions in the oceans or rocks. Scientists didn’t understand why it took so long to appear in the atmosphere.
Nickel and urea
The new study shows that two substances (nickel and urea) played a crucial role in delaying the oxygen accumulation. Nickel is a metal present in primitive oceans, and urea is a compound that is naturally formed in many processes. Experiments that simulated the ancient oceans conditions proved that high concentrations of nickel or urea stressed cyanobacteria and slowed their growth. Let’s explain this in more detail:
- Nickel: Moderate amounts of nickel helped cyanobacteria grow, but too much caused oxidative stress, stopping them from multiplying.
- Urea: High levels of urea made the cells accumulate toxic ammonia, causing them to die. Scientists discovered that more than 2 millimoles per liter of urea was harmful.
This means that, although cyanobacteria produced oxygen, its numbers were limited by these substances and stopped oxygen from accumulating in the atmosphere for hundreds of millions of years.
Oxygen finally transformed the Earth
With the passage of time, nickel levels in the oceans lowered and urea presence was stable, therefore, cyanobacteria could prosper. As a result, oxygen “pockets” began to form in certain areas of the ocean. Eventually, when conditions were right, cyanobacteria blooms increased enough to produce large amounts of oxygen, triggering the Great Oxidation Event.
This slow process explains why oxygen appeared in the atmosphere way after the cyanobacteria existed. It also shows how delicate the balance between life and chemistry was on our planet.
Earth and the pursuit of life on other planets
Lessons from the early story of Earth are very important for scientists that look for life on other planets. A planet can have organisms capable of producing oxygen, but if there are chemicals like too much nickel or urea, the oxygen could not accumulate in the atmosphere. This means that only looking for oxygen is not always enough to confirm the existence of life.
To study the story of Earth, researchers can better understand how to identify ‘’bio-signatures’’ on planets like Mars or icy moons like Europe and Enceladus.
Our planet shows that life can exist for millions of years without showing obvious signs in the atmosphere.
So…
Understanding this solves a mystery from our past and guides scientists in the pursuit of life on other planets. Earth reminds us that the interaction between biology and chemistry is complex, and that patience (both from nature and science) reveals surprising truths about our planet.
Isn’t it incredible how many things from now and the past we can learn thanks to the many researches scientists are doing?