Our Earth has finite resources and locations. After extinction of species, genera, or other categories, some resources, and, sometimes, locations, are freed up. The extinction of one species could allow other species to take advantage of those resources. Some species could use it to prolong their exitance or to diversify. It is also possible that other species would go extinct too due to missing links in a food chain. What else do we know about the after-extinction periods?
Big Numbers Helps and Sucks
An army of researchers studied the history of life on our planet for centuries. They discovered mountains of facts about various lived and living species. In 2011 a group of scientists estimated the number of eukaryote species as 8.7 million +-1.3 million. The wealth of data provides food for thought for scholars.
Yet, out of those 8.7 million species, only 14% of species on Earth and 9% of species in the ocean were described. Huge gaps in our knowledge make an analysis of individual extinctions and follow-up periods very difficult.
That is why our knowledge about trends in after-extinction periods comes mostly from two sources. The first one is an extensive study of the biggest, so called mass extinctions. The second one is a relatively new type of study. It involves a “big data” study, especially with the use of artificial intelligence as a tool.
When Big Radiation Comes?
There are fast and slow processes in evolution. “Adaptive Radiation is the diversification of a group of individuals into forms filling different ecological niches. Divergent evolution is a process of developing two or more species from a common ancestor over time.” The former is a fast process of evolution. The latter is a slow process of evolution.
For a long time, scholars associated the big scale of radiation after mass extinctions with a big scale of those extinctions. Multiple studies confirmed that.
The question is whether such a causality is the only one. It is not easy to answer this question. There are too much data and too much missing data to sort it out.
Mass Radiation Without Mass Extinction
Recent advancements in Artificial Intelligence (AI) made it possible to answer this question. A group of researchers applied machine learning to the Phanerozoic fossil record data from the Paleobiology Database. That project covered 1,273,254 occurrences for 171,231 species.
They found that among the 5% most significant periods of disruption there were “the ‘big five’ mass extinction events, seven additional mass extinctions, two combined mass extinction–radiation events, and 15 mass radiations.”. Moreover, they found that “comparable mass radiations and extinctions are typically decoupled in time”. In other words, the direct causal relationship between mass extinction and mass radiation is questionable.
Nevertheless, the ‘big five’ and other mass extinction are still counted among the top macroevolutionary disruptions in the last 550 million years. Such disruptions are among the most studied macro-evolutionary phenomena. We could not follow all such events. Instead, we will review just two of them – the oldest one and the newest one.
Is There Life Without Oxygen?
This question looks strange but it is not. For about half of Earth’s existence time, there was no oxygen in the planet’s atmosphere.
Do we know now when and why oxygen appeared in the Earth’s atmosphere? Yes, we do. It happened around 2.4 – 2 billion years ago. The biggest disruption in biological evolution was going on. The name of this event is the Great Oxidation Event. At that time the life on Earth already existed for about a billion years. However, there was very little oxygen in the air.
We know that all green plants are using photosynthesis to get their food. But those plants are not our heroes. The hero of our story is one bacterium, called cyanobacteria.
Yes, This Bacterium Is Our Hero
Billion years ago, that bacteria lived in the ocean. Cyanobacteria uses photosynthesis, and on the way, it produces oxygen as a waste product. Typically, in the ocean, the oxygen does not accumulate due to chemical reaction with the organic carbon. Only a small portion of oxygen will be freed up.
But give it a time, better a billion of years. Cyanobacteria enjoyed their position on Earth and thrive. Over time, that bacteria produced so many oxygen that the ocean became saturated with it. As a result, oxygen started to leak into the atmosphere. Welcome to the Great Oxidation Event (GOE).
The oxygen concentrations in the air increased. The number of oxygen using bacteria and, then, other living forms, which use oxygen, multiplied. The biological evolution speeded up. The fate of cyanobacteria is interesting. From a biodiversity viewpoint, the cyanobacteria moved into a small niche while organisms, which are using oxygen as an input, are now major players on the planet. On the other hand, cyanobacteria evolved and is a major component of phytoplankton in oceans and lakes. The phytoplankton is still a main source of oxygen on Earth.
In a sense, cyanobacteria gave birth to her gravedigger. Please remember this example. It was, probably, the first time on Earth when some organism created an existential threat to itself.
The recorded history of humanity is not the only history, from which we could extract valuable lessons for mankind. The game is different now. The battlefield is not the same too. The players and the rules were modified. Most important, the time scale shifted from hundreds of million years to hundreds of years. Yet, the lessons still could be applied if we have a will to learn.
Biosphere and Geosphere Interaction
Biological evolution is a big topic since Darwin’s times. Most discussions are wrapped up within that topic itself. Pretty rare we could hear or read about an interaction between the biosphere and geosphere on Earth. Furthermore, when we talk about this interaction, we assume that it happens in one direction. The climate and big global changes on earth, in oceans, and the air could have a dramatic impact on biological evolution. That is all fine.
What about the opposite direction? Could global changes in biosphere have a sizable impact on non-live portion of Earth? Yes, they could. The Great Oxidation Event is a prime example.
Pumping the oxygen into the atmosphere had a severe consequence not only for biological life. The atmospheric methane was replaced by carbon dioxide and water. Carbon dioxide is a weaker greenhouse gas. That, in turn, caused the global cooling. The named cooling of the planet triggered a series of ice ages.
People tend to overvalue the power of humans compare to other life on Earth. There is a discussion now – are we, humans, powerful and ignorant enough to push our planet into the climate change. Well, look again back at the Great Oxidation Event. The tiny cyanobacteria already forced the Earth into global cooling around 2 billion years ago. And that bacteria did not even have our most beloved treasures – consciousness and technology!
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