Rewrite the textbooks: Life on Earth did not arise due to increased oxygen levels

Forget everything you thought you knew about how life evolved on Earth. New research is challenging the longstanding belief that an uptick in oxygen levels during the Avalon explosion fueled the emergence of complex life hundreds of millions of years ago.

Between 685 and 800 million years ago, our planet underwent a significant shift in its biological inhabitants.

During this period, known as the Avalon explosion, our oceans, previously dominated by single-celled organisms like amoebas, algae, and bacteria, began to teem with more intricate multicellular life forms.

These included unusual sea sponges and relatives of modern mollusks. This transformative era was a prequel to the more renowned Cambrian explosion.

For nearly seven decades, scientists attributed this evolutionary leap to increased oxygen levels in the oceans. But a recent study led by researchers from the University of Copenhagen, in collaboration with the Woods Hole Oceanographic Institute, the University of Southern Denmark, and Lund University, is upending this theory.

Studying early oxygen levels on Earth

The research team examined the chemical makeup of ancient rock samples hailing from a mountain range in Oman, using these relics as a kind of time capsule to gauge oceanic oxygen levels dating back to the Avalon explosion.

In a stunning revelation, the data showed that oxygen levels at the time of the biological shift were actually 5-10 times lower than they are today. To put that in perspective, it’s equivalent to the oxygen concentrations found at twice the height of Mount Everest.

Associate Professor Christian J. Bjerrum has dedicated two decades to studying the conditions that surrounded the origin of life. She was quoted as saying:

“Our measurements provide a good picture of what average oxygen concentrations were in the world’s oceans at the time. And it’s apparent to us that there was no major increase in the amount of oxygen when more advanced fauna began to evolve and dominate Earth. In fact, there was somewhat of a slight decrease.”

Turning common knowledge upside down

This fascinating discovery rewrites a 70-year narrative that positioned higher oxygen concentrations as a crucial factor in the development of more advanced life forms.

Bjerrum stated, “The fact that we now know, with a high degree of certainty, that oxygen didn’t control the development of life on Earth provides us with an entirely new story about how life arose and what factors controlled this success.”

This shift in understanding may require reevaluating our foundational teachings and updating educational textbooks. Additionally, it opens new areas of exploration and encourages scientists worldwide to reinterpret their data and previous findings.

Bjerrum hopes this will stimulate research worldwide. “There are many research sections around the world, including in the United States and China, that have done lots of research on this topic, whose earlier results may shed important new details if interpreted on the basis that oxygen didn’t drive the development of life,” he said.

If it wasn’t oxygen levels, what was it?

This begs the question: if not oxygen, then what caused the proliferation of complex life during the Avalon explosion? Perhaps the answer lies not in an abundance of oxygen but rather its scarcity. According to Bjerrum, it’s possible that these early organisms benefited from the low oxygen levels, as the water chemistry would naturally protect their stem cells.

This hypothesis draws parallels to modern-day cancer research and the study of human and animal stem cells. “We know that animals and humans must be able to maintain low concentrations of oxygen in order to control their stem cells, and in so doing, develop slowly and sustainably. With too much oxygen, the cells will develop, and in the worst case, mutate wildly and perish. It is far from inconceivable that this mechanism applied back then,” Bjerrum concluded.

The researchers’ findings were corroborated by fossil evidence from three different mountain ranges across the globe: the Oman Mountains in Oman, the Mackenzie Mountains in northwest Canada, and the Yangtze Gorges area of South China. The team employed Thallium and Uranium isotopes found in these ancient mountains to calculate oxygen levels from the time of the Avalon explosion.

As we delve deeper into our planet’s distant past, we continue to refine and reshape our understanding of life’s fascinating journey on Earth.

More about primordial Earth and early oxygen levels

Primordial Earth, or the early Earth, refers to the period of our planet’s history that stretches from its formation about 4.54 billion years ago to the beginning of the Cambrian Period, around 541 million years ago.

This vast expanse of time, known as the Precambrian eon, is subdivided into the Hadean, Archean, and Proterozoic eons.

Hadean Eon (4.6 – 4.0 billion years ago)

The Earth began to form in the Hadean eon, around 4.54 billion years ago, in the dust and gas disk (protoplanetary disk) surrounding the young Sun. The process involved collisions and coalescence of cosmic debris, eventually forming the Earth.

During the Hadean eon, the young planet was extremely volatile and inhospitable. It was likely covered in molten rock due to the constant bombardment from other celestial bodies and intense heat from radioactive decay. This period saw the formation of the Earth’s initial crust and the earliest oceans (of magma).

The Moon was also formed during this period, likely as a result of a massive collision between Earth and a Mars-sized object, often referred to as Theia.

Archean Eon (4.0 – 2.5 billion years ago)

The Archean eon is characterized by the formation of the Earth’s continental crust. The molten surface cooled down to form a solid crust, and water started to condense and form the first oceans. Life began to appear during this period.

The atmosphere of the Archean Earth was vastly different from what we have today. It was mainly composed of methane, ammonia, water vapor, and carbon dioxide, with very little to no free oxygen.

Around 3.5 billion years ago, simple life forms, such as prokaryotes (cells without a nucleus) began to appear. This includes cyanobacteria, formerly known as blue-green algae. These organisms were significant as they used sunlight to make food—a process known as photosynthesis—and started producing oxygen as a waste product.

Proterozoic Eon (2.5 billion – 541 million years ago)

Until this recent study, it was widely believed that the Proterozoic eon saw a dramatic increase in oxygen levels in Earth’s atmosphere. This event was known as the Great Oxygenation Event. This happened due to the continuous oxygen production by cyanobacteria.

Oxygen levels were believed to have played a critical role in shaping life on Earth. It led to the formation of the ozone layer, which shields the planet’s surface from harmful ultraviolet radiation, allowing life forms to inhabit land. It also allowed for more complex, multicellular organisms to evolve.

This era also witnessed the formation of supercontinents, which later broke apart and began to resemble the modern configuration of our continents.

Towards the end of the Proterozoic eon, around 800 million to 600 million years ago, Earth experienced extreme glaciation events known as “Snowball Earth,” where the entire planet was possibly engulfed in ice.

Emergence of complex life during the Avalon explosion

The Precambrian eon ended with the start of the Cambrian Period, marked by the “Cambrian Explosion” of life. This period, starting around 541 million years ago, saw a rapid increase in the complexity of life forms and the emergence of most of the major groups of animals that we know today.

Despite covering nearly 90% of Earth’s history, the Precambrian era is less understood than the periods that follow it. This is largely because the geological record from that time has been heavily metamorphosed, and fossils from that era are scarce. However, what we do know paints a fascinating picture of a world that was vastly different from the Earth we inhabit today.

More about the Avalon explosion

The Avalon explosion, which took place approximately 575 to 565 million years ago, is notable for the emergence of a wide range of large, complex organisms, collectively known as the Ediacaran biota.

These life forms were incredibly diverse, differing significantly from the life forms that exist today, and they do not fit neatly into our current categories of animals, plants, or fungi.

Dickinsonia

One of the most famous life forms from the Ediacaran Period is Dickinsonia. These were oval-shaped organisms that could reach up to a meter in length. They appeared to have segments or units running longitudinally down their bodies. Whether Dickinsonia was an animal, a type of fungus, or a completely separate group of life forms is still a topic of debate among scientists.

Charnia

Charnia is another iconic Ediacaran life form. It had a frond-like appearance, with branches coming off a central stem. This creature was anchored to the sea floor and likely absorbed nutrients directly from the water around it. Like Dickinsonia, the exact classification of Charnia is uncertain.

Spriggina

Spriggina was a small, bilaterally symmetrical organism that may have been an early arthropod. It had a segmented body, and it is speculated that it might have been one of the first predators.

Fractal organisms

There were also many Ediacaran organisms that showed a fractal pattern in their body structure, meaning they had repeated patterns at different scales. These include rangeomorphs, such as Charniodiscus and Rangea, and erniettomorphs, such as Ernietta.

Other Ediacaran organisms

Many other organisms from this period are difficult to categorize. Some, like Tribrachidium, were radially symmetrical with three arms, while others, like Kimberella, show possible similarities to modern mollusks.

Most Ediacaran life forms were soft-bodied, which makes their preservation in the fossil record quite remarkable. The exact relationships of these organisms to modern groups are still uncertain.

Research into these enigmatic life forms continues. They represent an important phase in the evolution of life on Earth, filling the seas with diverse, multicellular organisms for the first time in Earth’s history.