The earth has experienced five mass extinction events. What can we learn from them? | Daniel H. Rothmann


F.Five times in the last 500 million years, more than three quarters of marine species died from mass extinction. Each of these events is associated with a significant disruption of the earth’s carbon cycle. How such catastrophes come about remains a mystery. However, more recent research increasingly points to the possibility that the earth system – life and the environment – can experience a cascade of disruptions if it is stressed beyond a turning point.

With the world’s leaders meeting at Cop26 in Glasgow, it makes sense to get involved in specific goals like limiting warming to 1.5 ° C. If we don’t achieve such a goal, we will soon know. Mass extinctions, on the other hand, can take tens of thousands of years or more to peak. But if they are indeed the result of a disruptive cascade, we must act now to prevent such a runaway process.

To see why, first let’s point out what we know.

Chemical analyzes of old sedimentary rocks tell extraordinary stories of environmental changes. A common element in these narratives is a crisis. Somehow the earth system reaches a turning point where small fluctuations become large. In some cases, mass deaths occur.

Many of these events are associated with increased releases of carbon dioxide (CO2) of volcanic eruptions. At least three of the five major extinction events occur at such times.

But volcanic release of CO2 are too weak to explain the severity of environmental crises alone. Scientists are therefore also considering other potential stressors. One idea focuses on the release of methane, a powerful greenhouse gas. Another hypothesis assumes that volcanoes effectively blast sediments that are rich in coal or other organic material and thereby convert them to CO. could convert2.

My own recent research suggests that such ascriptions are unnecessary on a case-by-case basis. It turns out that the worst environmental crises fall into one of two groups. In one group – the majority – the carbon content typically increases. In the other – four of the five major mass extinctions – the carbon content rises a little faster.

If the carbon cycle is forced out of balance too quickly, it can reach a tipping point beyond which the cycle itself greatly increases the initial fluctuation. The resulting disruption of the earth system would then have the intrinsic properties of the carbon cycle rather than the particular properties of the disruption that triggered the disruption. This reasoning explains the usual rate at which carbon levels have often increased in the past. It also reflects well-established properties of complex nonlinear systems.

From this point of view, mass extinction events are being driven not only to the tipping point, but beyond. The added kick can be responsible for their lethality.

Let us now return to the risk of modern disaster. Human activities currently produce CO2 CO produced much faster than massive volcanism2 in the past. While that seems frightening, we have to acknowledge that the lead up to past crises is much longer than modern climate change. This means that the modern tipping point as total CO. can be expressed2 Production instead of speed. A simple calculation suggests that if we were to CO. do not reduce significantly,2 Emissions, then we risk crossing the threshold before the end of this century.

This reasoning does not exclude alternative explanations that rely on specific carbon sources. Furthermore, the available data do not rule out mechanisms, such as ecological changes, that could hold up an out of control process before it becomes severe. Nevertheless, the calculations are consistent with our current understanding of the carbon cycle.

These ideas are part of an ongoing scientific effort to unravel some of the deepest mysteries of our past, not only to improve our understanding of the risks of modern climate change, but also to find out how our world was created. And therein lies a message to our political leaders meeting at Cop26: let’s not add to the sixth extinction threat. Efforts to limit CO2 -Emissions may pay off more in the future than we can imagine.


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