Two rival models of how life on Earth continues to exist thrashed it out on Saturday at Royal Holloway University as part of the British Science Festival. In the red corner was Dr David Wilkinson of John Moores University with the Gaia concept, the theory that, once established on our planet, life actively regulates the conditions that enable us to remain here. And in the blue corner was Royal Holloway’s Dr Dave Waltham defending the Goldilocks hypothesis, which suggests that life is only able to remain on Earth by chance alone.
Both speakers initially had 20 minutes to make their case before taking turns to reply to eachother’s arguments. Then, the audience was invited to vote on which theory they found most convincing.
I personally came to the talk a Goldilocks follower. Surely given the sheer number of happy accidents, from asteroids wiping out the dinosaurs to how the balance of gases was tipped in our favour, the fact that life had continued to exist on this planet up until now was down to luck, pure and simple.
To a certain extent, the Gaia hypothesis doesn’t contest this. According to Wilkinson, Gaia acknowledges that a large amount of luck was necessary for life getting started in the first place. Both theories start from the point where life is already established and abundant on Earth. But that is where the agreements tend to end. Gaia suggests that life helps keep those conditions suitable for life within fairly limited parameters, whereas Goldilocks says that this too is down to luck, and that a “self-regulating” planet is a myth.
It was a tightly-fought contest between two highly convincing proposals. Wilkinson went first, and reminded the audience of the Black Swan theory and related it to Gaia by saying how difficult it is to come to a sound conclusion about life on Earth when we only have one piece of evidence to go on: our planet.
Waltham then set out his argument by showing an image called the Hubble Deep Space Field, which is the most distant image captured by the Hubble Space Telescope.
“If I’m right, there is no complex life out there in the Hubble Deep Space Field shot,” said Waltham. “According to the Gaia argument, there should be billions. But there are so many factors necessary to get conditions just right to have a stable climate, one of them being orbit. The probability is that there will be one planet in 10 million galaxies in the visible universe that will have all the nine basic properties necessary for life to start.”
“Neither of us disagrees that evolution is very important for the endurance of life,” said Waltham. “But my point is, does life only do good things for the planet? Sometimes it does destructive things.
“Take the oxygen crisis two to three billion years ago. Oxygen levels took off, and that had a terrible effect on the Earth. Not only did it cause a bad climate effect, but it poisoned most life on Earth, which at that time couldn’t handle oxygen.
“I don’t disagree that the oxygen levels worked out well in the long term. But where I get queasy is the notion that life regulates conditions on the planet to continue its existence.”
Wilkinson responded to the oxygen argument, answering: “That oxygen poisoned life is overplayed and oversimplified. When oxygen levels went high, there would have been a lot of life that those conditions were fine for.
“The case for Gaia is that the Earth regulates itself. The parameters within which life can exist on Earth are rather small. But life may be intimately involved in keeping the conditions of life on Earth stable. Once you make life important in the system, it’s more likely to stay within life-friendly conditions. That’s not to say that once we have life, the planet will always stay within those favourable limits, but it biases the dice in favour of it.”
He cited as an example the fact that the sun has got much bigger throughout its existence but the temperature on Earth has stayed the same, and the water has not boiled away. But he added that self-regulation can’t work for ever.
“When you say regulation to someone, they expect it to stay completely constant. But it actually oscillates between boundaries. You can’t attain a stable regulation forever.
“When it fails, you get a big jump in temperature. Finally the system can no longer keep it all level. But if it failed, then it might then swap to another system of regulation.
“And you can still use Gaia theory in a purely chance world. Gaia defines life in terms of its persistence rather its amount. But diversity of life is important because it gives you a wider range of options and so if conditions change, there is more chance that some life will survive.”
As I listened, I found myself being won over by whatever argument was being put forward by the time (fickle I), testament surely to the power of each theory, but I eventually opted for Gaia. In the end, the audience vote was right down to the wire, with Gaia clinching it by a mere two votes.
But thanks to a lively debate, a central and ongoing clash of ideas was brought to life, which was ultimately a success for both sides.
Earth image courtesy of NASA
Hubble Deep Space Field image courtesy of hubblesite.org
Audio recorded by myself at the talk.