To move something left and right you need two reins. To move something in two dimensions you need four reins, and so on. Ecosystems can be very complex with a very large number of species, but rather than being destabilising, this diversity can actually produce many reins that stabilise environmental conditions.
Life on Earth affects environmental conditions as well as being affected by them, resulting in a planet-wide, self-stabilising control system, say University of Southampton researchers…
Dr James Dyke
Appearing in the open access journal PLOS Computational Biology
this week, a paper from scientists at the University of Southampton proposes a solution to the controversy that has long surrounded the question of the stability or otherwise of the Earth system.
As arguably the most complex system in the known universe, the Earth, with its oceans of liquid water, core-driven magnetic field, dynamic climate and mobile lid tectonics has sustained life for three and a half billion years. But how have life forms survived the planetary-scale disasters and changes which have been occurring since then?
Dr James Dyke, the lecturer in Southampton’s Electronics and Computer Science (ECS) department who authored this study alongside PhD student Iain Weaver, believes that a complex feedback system not unlike that proposed in the Gaia theory could explain the stability of life on Earth.
James Lovelock first proposed the Gaia hypothesis in the 1960s as a result of his work on life detection on Mars. He realised that, given our understanding of Martian geology, there should be no need to send a probe to the Martian surface. Rather, he argued that predictions and observations of the atmosphere of the red planet with Earth-based telescopes would allow us to conclude that Mars could not support life. The composition of gases in the Martian atmosphere is very stable and close to chemical equilibrium, unlike that of the Earth’s atmosphere.
"Our planet is far from equilibrium and this state is importantly maintained by life forms such as photosynthetic organisms," explained Dr Dyke in an interview with ScienceOmega.com
. "Future missions looking for life on exoplanets will use the same reasoning – that there are a range of 'biomarkers' that we will hopefully be able to see with ground or space telescopes.
"What has proved very controversial is the notion that life on Earth has been actively participating in the evolution of the Earth system, and that this co-evolution has produced a system that is self-stabilising or homeostatic, in a similar way to biological organisms."
Why should the Earth be homeostatic?
As Dr Dyke pointed out, every organism alive today can trace its ancestry back to the origins of life. Life has held on despite massive impacts, significant changes in the Sun and extreme volcanism. This could just be down to luck, or – as Dr Dyke and Weaver suggest – the effects of life on the planet may have lead to the planet being better able to support life.
"The fundamental stumbling block has always been an absence of any understood mechanism or process that could explain why interacting life-environmental systems should be stable, or at least be more likely to be stable as opposed to unstable," Dr Dyke said. "If life stabilises some aspects of its environment, why should it not also be able to destabilise it and wipe itself out?"
The current paradigm for understanding the evolution of life on Earth is neo-Darwinism. Although evolution can account for the diversity of species, it cannot explain how the planet has changed over time. The Southampton researchers have now shown that a very simple mechanism called 'rein control' can emerge from ecosystem interactions.
"It's called rein control because it's like steering a horse with reins – they can only pull, not push and pull," Dr Dyke explained. "To move something left and right you need two reins. To move something in two dimensions you need four reins, and so on. Ecosystems can be very complex with a very large number of species, but rather than being destabilising, this diversity can actually produce many reins that stabilise environmental conditions."
After simplifying existing models and theories in order to get at the central assumption that life affects environmental conditions which in turn affect life, the team built some simple mathematical models which showed that environmental conditions become stabilised.
"Taking our analysis further required much faster computers, such as the Iridis supercomputer at the University of Southampton," said Dr Dyke. "We used a technique based on Gaussian processes to show that environmental homeostasis was a very robust result, and in particular that it wasn't affected by biodiversity or ecological complexity."
'A good contemporary example'
The organisms affecting the environment must 'feel' the consequences of their effects in a feedback loop for homeostasis to emerge. In a control systems context, this means there must be sufficient information flow within the system. While the extent of current information flow on the Earth is an open question, destabilising events in the past include the 'great oxidation', which was the result of the evolution of photosynthesis.
"Some of the mass extinction events in the past may in fact have been largely driven by life," noted Dr Dyke. "Our current concerns with greenhouse gas emissions and climate change seem to be a good contemporary example.
"Our species is changing the composition of the Earth's atmosphere and this is beginning to have impacts on the environment that will affect other organisms. It hasn’t had much of an impact on Homo sapiens
– yet – but if we carry on with business as usual then the predictions are not good. In time we will feel the consequences of our actions with destabilised food production, extreme weather events, flooding, and so on."
Much larger changes will be required to reduce these impacts if and when this situation arises, and Dr Dyke commented that feedback will then be evident at another level.
"The countries that are largely responsible for carbon dioxide emissions are the most industrialised," he said. "These are typically the richest countries and the best placed to insulate themselves from the worst consequences of their actions. The irony, of course, is that those countries that contributed least to the problem will be those that will suffer the most."
Click here to read the full text of the research paper...