When Worlds Come Alive

Like Earth, do some exoplanets have a self-regulating terrestrial biosphere, asks MUKUL SHARMAIn the Tarkovsky film, Solaris, an entire oceanic planet to which a group of astronauts have journeyed, turns out to be living. So, while they think they are probing and analysing an inanimate world below them from their hovering research station, in reality they themselves are also being studied by the world which is probing and examining their thoughts.Gaia HypothesisIf the idea of a sentient planet seems too magical even for science fiction, imagine how we might react if told that something of the same nature could be applicable to Earth too. Because that’s pretty much what sometime Nasa consultant and independent scientist James Lovelock proposed with his ground-breaking Gaia hypothesis in the late 1960s. Named after the Greek Earth goddess, the hypothesis postulates that the terrestrial biosphere is a self-regulating entity with the capacity to keep our planet healthy by controlling the chemical and physical environment. That, in fact, the Earth’s atmosphere, oceans and biota form a tightly coupled system which maintains environmental conditions close to optimal for life.In short, living and non-living parts of the Earth form a complex interacting system that can be thought of as a single organism.Those who find it hard to swallow the notion that anything as large and apparently lifeless as the Earth can be alive, should listen to Lovelock. “The difficulty can be lessened,” he writes, “if you let the image of a giant redwood tree enter your mind. The tree undoubtedly is alive, yet 99 per cent of it is dead. The great tree is an ancient spire of dead wood, made of lignin and cellulose by the ancestors of the thin layer of living cells which constitute its bark. How like the Earth, and more so when we realise that many of the atoms of the rocks far down in the magma were once part of the ancestral life of which we all have come.”But is there any scientific evidence that the Gaia process has shaped the planet in a way that’s made it optimal for life? Because without such evidence, the theory remains at best a quaint pseudo-scientific exercise in fantasy. Actually there is, and scientists have discovered many mechanisms which show how this living system has automatically controlled global temperature, atmospheric content, ocean salinity and other factors that maintain its own habitability.Take global temperature. Since life started on Earth, the energy provided by the Sun has increased by almost 30 per cent - yet, the surface temperature of the planet has remained within the levels of habitability. One way this is achieved is through cloud formation over open ocean that is almost entirely a function of the metabolism of oceanic algae that emits a large sulphur molecule as a waste gas which becomes the condensation nuclei for raindrops. Cloud formations not only help regulate Earth’s temperature, but it’s also an important mechanism by which sulphur is returned to terrestrial ecosystems.Or take atmospheric content. The Gaia hypothesis states that the Earth’s atmospheric composition is kept at a dynamically steady state by the presence of life. And that’s a fact because all atmospheric gases other than some trace element noble gases present in the atmosphere are either made by organisms or processed by them. As a result, the stability of the atmosphere on Earth is not a consequence of chemical equilibrium as it is in planets without life.A Fine-tuned UniverseToday, when so many hundreds of exoplanets outside our solar system have also been discovered, some people are already wondering if some of these worlds may not have come alive through a similar Gaia-like process. Or that planetary Gaia might only be a microcosmic paradigm for the entire universe, which could in turn be self-regulated by all the living systems in it, in order to maintain cosmic habitability. Perhaps that’s why the anthropic principle exists - a principle that states the universe seems so fine-tuned for life that if any one physical parameter were to vary by an infinitesimal amount, life would not have arisen anywhere in it.