[ad_1]
We will probably never know how life on Earth began. Maybe in a shallow sunny pool. Or in the depths of the ocean crushing miles below the surface near the crustal crust that spat out a rich mineral soup. Although there is good evidence of life at least 3.7 billion years ago, we do not know exactly when it started.
But these eons produced something even more remarkable: life persisted. Despite the massive impacts of asteroids, cataclysmic volcanic activity and extreme climate change, life has managed not to cling to our rocky world but to thrive.
How did this happen? The research we recently published with colleagues in Trends in Ecology and Evolution offers an important part of the answer, providing a new explanation for Gaia's hypothesis.
Developed by scientist and inventor James Lovelock and microbiologist Lynn Margulis, the Gaia hypothesis originally proposed that life, through its interactions with the earth's crust, the oceans and the atmosphere , produced a stabilizing effect on the conditions of the planet's surface, especially on the composition of the atmosphere and climate. With such a self-regulating process in place, life could survive in conditions that would have annihilated it on non-regulatory planets.
Lovelock formulated Gaia's hypothesis when working for NASA in the 1960s. He acknowledged that life was not a passive passenger on Earth. On the contrary, it has profoundly reshaped the planet, creating new rocks such as limestone, affecting the atmosphere by producing oxygen and causing cycles of elements such as nitrogen, phosphorus and carbon. Man-made climate change, which is largely the result of the burning of fossil fuels and releasing carbon dioxide, is the last way in which life affects the Earth's system.
It is now recognized that life is a powerful force. , the Gaia hypothesis remains controversial. Despite evidence that surface temperatures have, with a few exceptions, remained within the range required for widespread liquid water, many scientists attribute this to good luck. If the Earth had completely descended into a cooler or warm house (think Mars or Venus) then life would be gone and we would not be here to ask how it had lasted so long. This is a form of anthropogenic selection argument that says there is nothing to explain.
Clearly, life on Earth has been lucky. In the first case, the Earth is in the habitable zone – it orbits the sun at a distance that produces the surface temperatures required for liquid water. There are alternative life forms and perhaps more exotic in the universe, but life as we know it requires water. Life has also been lucky to avoid very large impacts of asteroids. A piece of rock significantly larger than the one that led to the disappearance of the dinosaurs 66 million years ago could have completely sterilized the Earth.
See all best photos of the week in these slideshows
But what would have happened if life could have pushed one side of the scales? And if life somehow did its own luck in reducing the impacts of planetary disturbances? This leads to the central question unresolved in Gaia's hypothesis: how is planetary self-regulation supposed to work?
Although natural selection is a powerful explanatory mechanism that can explain much of the observed change in species over time, there was a lack of a theory that could explain how living and non-living elements of a planet produce self-regulation. Therefore, the Gaia hypothesis has generally been considered interesting but speculative – and not based on a testable theory
Choosing stability
We think we finally have an explanation of Gaia's hypothesis. The mechanism is "sequential selection". In principle, it is very simple. As life emerges on a planet, it begins to affect environmental conditions, and it can organize into stabilizing states that act like a thermostat and tend to persist, or destabilize fugitive states such as Earth's events. which have almost extinguished the beginnings of complex life. 600 million years ago.
If it stabilizes, then the scene is set up for a later biological evolution that will reconfigure with time all the interactions between life and the planet. A famous example is the origin of photosynthesis producing oxygen about 3 billion years ago, in a world previously devoid of oxygen. If these new interactions stabilize, then the planetary system continues to self-regulate. But new interactions can also produce disruptions and uncontrolled feedback. In the case of photosynthesis, it led to a sharp increase in atmospheric oxygen levels in the "Great Oxidation Event" about 2.3 billion years ago. It was one of the few periods in the history of Earth where the change was so pronounced that it probably erased much of the current biosphere, effectively restarting the system.
The chances of life and the environment spontaneously organize into self-regulating states. higher than expected. If done, given the sufficient biodiversity, it can be extremely likely. But there is a limit to this stability. Pushing the system too far can go beyond a tipping point and quickly collapse to a new and potentially very different state
This is not a purely theoretical exercise, as we think we can test the theory in a number. in different ways. At the smallest scale that would involve experiments with various bacterial colonies. On a much larger scale, this would involve looking for other biospheres around other stars that we could use to estimate the total number of biospheres in the universe – and therefore not just the probability of ## 147 ## Emergence of life, but also persistence. [19659002]
The relevance of our discoveries to current concerns about climate change has not escaped us. Whatever humans are, life will continue one way or the other. But if we continue to emit greenhouse gases and thus change the atmosphere, we risk producing dangerous and potentially dangerous climate change. This could eventually stop human civilization affecting the atmosphere, if only because there will be no more human civilization.
Gaian self-regulation can be very effective. But there is no evidence that she prefers one form of life to another. Countless species have emerged and then disappeared from the Earth over the past 3.7 billion years. We have no reason to believe that Homo sapiens are different in this respect
James Dyke, Associate Professor of Sustainable Development Science, University of Southampton and Tim Lenton , Director, Global Institute of Systems, University of Exeter
This article was originally published on The Conversation. Read the original article.
[ad_2]
Source link
