By Debkumar Mitra
The year has been identified: 2100. Only the date is yet to be announced. The sixth mass extinction may obliterate life like it had happened five times on Earth in the past. So, is it time to make plans to leave the planet? If media headlines are to be believed, then science has finally agreed with Hollywood scriptwriters of disaster films: the end is less than 100 years away.
That end could be much swifter, of course, if North Korea and the US start anuclear war. But before we decide on building our moon-bound catamaran let us examine what Daniel Rothman, professor of geophysics in the MIT Department of Earth, Atmospheric and Planetary Sciences, has predicted in his paper, ‘Thresholds of Catastrophe in the Earth System’, published in the journal Science Advances (goo.gl/n8yWV5).
In the 540 million-year history of life on the planet, Earth has been witness to five mass extinction events. According to Rothman’s hypothesis, mass extinction in the past has occurred when one of two thresholds was crossed. These thresholds are linked to carbon cycles and timescales.
Carbon cycle describes the process by which carbon, the fourth most-abundant element on Earth, in its many forms moves between the atmosphere, oceans, biosphere and geosphere. In the past, globally fatal changes in carbon cycles served as the trigger for mass extinction of marine species around the world.
The two thresholds, as described by Rothman’s mathematical model, can be summarised as: one, if the changes in the carbon cycle occur over a long period of time then mass extinctions will follow if those changes occur at rates faster than global ecosystems can adapt.
The second threshold is dependent on carbon cycle changes over shorter timescales. In this case, how fast these changes are occurring is not important for triggering mass extinction. What is important is the size or magnitude of the change.
According to Rothman, due the sharp spike in CO2 emissions over a relatively short timescale, the latest extinct event will depend on “whether a critical amount of carbon is added to the oceans”. His calculations put the amount at about 310 gigatonnes. Now the clincher: given the rate at which human activities are adding carbon to oceans of the world, the critical amount will be reached by 2100 and, thus, probably start the sixth mass extinction.
How reliable is Rothman’s mathematics? Till such time someone comes up with a counter-example, the model with its boundary conditions is true. However, the notion of certainty associated with the study of mathematics is not unquestionable.
The certainty of a mathematical system depends on its consistency. Such asystem is consistent if there are no contradictions possible within the system. There should not be any mathematical statement within the system whose truth value is ambiguous — that is, both ‘true’ and ‘false’ at the same time.
Also, despite its widespread use across knowledge systems, mathematical modeling has enjoyed less success in biosystems such as ecology, human behaviour, long-term weather forecasting, and in those systems where predictability is limited to statistical descriptions.
In these areas, however, there seems to be an increasing reliability on the predictive power of mathematical modeling and simulation. All things considered, Rothman’s paper is significant.
It opens a door to a future that may be unpalatable but probable. It also serves as a timely reminder of how humans are tinkering with natural cycles without realising the consequence.
Sometimes headlines such as ‘Mathematics predicts mass extinction on Earth in less than 100 years’ cause hysteria and confusion at global scale. While no one can fault the headline, there is lot more to the story.
First, mass extinction events are not one-day cricket matches that are gradual processes which happen over a long period of time. Rothman has said that his model is not predicting disaster happening the next day. “It’s saying that, if left unchecked, the carbon cycle would move into a realm which would be no longer stable, and would behave in a way that would be difficult to predict. In the geologic past, this type of behaviour is associated with mass extinction,” he says.
Suppose the mass extinction event sets in as per Rothman’s model. Will the human species be able to escape it? The pre-Cambrian mass extinction wiped out nearly 95% of marine species. So there is a small probability that humans will survive the catastrophe.
What if we do not escape Nature’s wrath. Will we reappear on Earth? Harvard evolutionary biologist Stephen Jay Gould once said if we rewind the evolutionary tape of life on Earth and play it again, there is no guarantee we will be watching the same film.