How early life forms caused climate change, but found an equilibrium
Rather than causing climate disasters, this life-driven climate change settled into a sort of equilibrium, brought about by the biosphere’s stabilizing mechanisms
This image released by NASA in 2017 shows two decades of satellite data on the colour of Earth's reflective light, illustrating where plant life is growing.
By searching for food and shelter, animals have been causing global warming as long as they have existed on the Earth, new research shows.
But rather than causing runaway climate disasters, this life-driven climate change repeatedly settled into a sort of equilibrium, brought about by the biosphere’s natural stabilizing mechanisms.
The interplay between these two factors — life seeking its own procreation no matter the environmental cost, in a climate that is finely sensitive to the changes brought about by life — has long been mysterious and alluring.
For example, the notion that the Earth and its living creatures function, in sum, as a kind of unified organism is known as the Gaia Hypothesis, and has been influential since the environmentalist scientist James Lovelock proposed it in the 1970s.
Now, two new research papers co-authored by Tim Lenton, director of the Global Systems Institute at the University of Exeter in England, cast light on this ancient dynamic, and show how plausible it is to regard Earth and its life forms as a single evolutionary unit.
The story begins at the bottom of the ocean in the Palaeozoic Era, in which newly evolved marine animals started burrowing into the sediment that had been laid down by earlier life forms that had grown into “mats,” like algae. First it was just little worms, then bigger worms, and then sediment-dwelling predators and spider-like trilobites. As they disturbed the sediment, they freed up buried organic material.
Solids moved up and down through the ocean’s layers, and the concentrations of soluble materials were changed. The organic material then decayed as it was exposed to oxygen, which freed up carbon dioxide, in a similar process that happens today as permafrost melts.
In effect, these burrowing animals were changing the chemical makeup of the oceans and skies, and thus the climate.
Scientists have previously studied the impact of this “bioturbation” on cycles of phosphorus, oxygen and sulphur, but until now their combined effects have resisted the efforts of climate modelling.
The new paper in Nature Communications proposes a way to model them together, and it identifies this “shallow burrowing” as a “significant potential driver of environmental change at a pivotal juncture in Earth history.”
It ended up causing a “low-oxygen state” that lasted 100 million years, the paper reports.
“The evolution of burrowing animals appears to be one of those cases where a new kind of biology ends up disrupting the composition of the atmosphere and the climate,” Lenton told the National Post. “Then the whole system has to re-find a new stable balance, which it did in this case at a lower oxygen level and with a hotter climate, until land plants came along 450 million years ago and started to push up the oxygen and cool things down again.”
The other paper, in the journal Trends in Ecology and Evolution, is a more theoretical analysis of the way life and climate interact, in which the “shallow burrowing” is just one of many examples.
By creating negative feedback loops, life forms can stabilize Earth’s climate. But life changes, and when new life forms evolve, the climate system can be disrupted. If these new forms create positive feedback loops, life can destabilize climate even to the point where it is no longer habitable for those creatures. At that point, the destabilizers die out, the life-climate system resets, and new life forms eventually take their place.
This is what allows for what Lenton calls “sequential selection,” as stabilizing effects are locked in temporarily, until the biosphere periodically resets itself.
“Initially, the effects of life may be destabilising or stabilising, but if they are destabilising this doesn’t tend to persist, so the system continues to change and ‘search’ until it falls into a stable attractor,” Lenton said.
He said the key thing to remember, for humans dealing with their own climate disruption, is the vast time scales on which these natural changes happen.
“For me, the moral of the tale of Earth history is that if we leave it to evolution to re-stabilize our planet from the climate disturbance we are creating it could take millions of years,” Lenton said. “But we have conscious foresight, technology, etc, so if we really are Homo sapiens (wise (wo)man) then we will use our skills to re-stabilize our life-support system a whole lot quicker than that. For me that means more lessons from the biosphere: powering our future civilization with sustainable (mostly solar) energy and doing much more recycling of all the materials we build our civilization out of and feed ourselves with.”
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