In part 1 of this Gaia hypothesis series, we left off with the question:
What led Lovelock to suspect this planet wasn’t just a rock floating through space?
At NASA, James Lovelock looked at ways to detect life on Mars by atmospheric analysis. He and a partner used Earth as a model and combined data on solar radiation, atmosphere, and oceans. After considering Earth conditions as if from outer space, they discovered that the Earth was being regulated from the surface.
Here is a simple summary of his findings:
The Improbabilities
“The climate and the chemical properties of the Earth now and throughout its history seem always to have been optimal for life. For this to have happened by chance is as unlikely as to survive unscathed a drive blindfolded through rush-hour traffic.”
Temperature
Despite periods of warming and cooling over the 3 billion years this planet has hosted life, the surface temperature has remained relatively constant. The sun, however, has not. What might be considered our sole source of radiant heat has increased its output by 25%. With that much less heat, early Earth would have been completely frozen. It only takes a 2% temperature decrease to create an Ice Age.
How has this planet maintained its comfortable temperature while the sun heated up?
“What parts of herself, I wonder, does she use as the thermostat?”
Atmosphere
The chemical composition of this planet’s atmospheric gases has been in a constant state of disequilibrium since life began. This violates the rules of chemistry and suggests an active control mechanism is at work.
“Our experiments . . . convinced us that the composition of the Earth’s atmosphere was so curious and incompatible a mixture that it could not possibly have arisen or persisted by chance.”
Despite this highly improbable disequilibrium, planetary oxygen levels have remained at 21%. This is an upper safe limit for life. Even a slight increase in oxygen (1%) would increase the likelihood of forest fires. At 25% oxygen, fires would spark so easily it would be hard for vegetation to survive.
How is it possible that oxygen remains at a consistently safe level?
Ocean Salinity
The salinity of the ocean has remained at a stable, safe limit for marine life over 100s of millions of years. The average salinity of the ocean is 3.5%. For a living cell to survive, the salt content of its internal or external environment can’t exceed 6%. Beyond that point, the cell disintegrates.
The main sources of salt in the sea are runoff from land and sea floor spreading. The amount of salt washed into the ocean from the land alone, over millions of years, is enough to have raised the salt concentration well beyond the 6% upper limit for life.
What mechanism has been reducing salinity and keeping the ocean habitable?
Recognizing this series of improbabilities, Lovelock set out to find planet-wide processes that might explain them. His purpose was to provide scientists with further areas to research.
For our non-scientific purposes, he wanted to answer the question:
How to prove that Mother Earth lives?
In part 3, I’ll explain some of the ways Gaia may be using life to manage this planet.
Missed the introduction? part 1
Sources:
- James Lovelock, Gaia: A New Look at Life on Earth
- James Lovelock, We Belong to Gaia
The Gaia Hypothesis, Part 1