Talk at the Geological Society of London, on 5 May 2011.
This building was once part of Burlington House and owned by the Duke of Devonshire. In 1850 it was bought by the Government and made into a centre for the Arts and Sciences. The main house was shared by the two Royal Academies for Arts and Science and soon the disciplines of science formed their separate societies here around the courtyard. This centre lasted almost 100 years until in 1968, needing more space the Royal Society moved to its present home in Carlton House Terrace.
In the 1960s Geology was mainly about the rocks and sediments and greatly excited by the discovery of plate tectonics. Biology was occupied with neo Darwinism and the dynamics of natural selection. Discussions between Earth and Life scientists were friendly and mostly about where to find the best fossils. It is true that a few geniuses like Redfield, Hutchinson, Lotka, and Sillen had asked awkward questions before the 1960s and the Russian scientist Vernadsky spoke about life as a geological force but academic science was unruffled and continued to teach Earth and Life science separately as before.
Chemists and physicists were deeply moved as were we all by their discovery that the genome was carried by the helical molecule DNA. The depth of this discovery may have overshadowed the significance of the discovery of the mechanisms of photosynthesis and its role in oxygenating the atmosphere. Yet, because scientists thought almost wholly in the terms of whatever was their specialty they left unchallenged the notion that oxygen in the air came from the photochemical dissociation of water in the upper atmosphere. Few seemed to wonder why there was so little carbon dioxide in the air.
By the start of this century our view of the Earth was vastly changed, and in a way this meeting celebrates the revolution in the way we think about the Earth. As often happens in science a force behind this revolutionary change was war. Darwin, like Newton before him, received support from the British Admiralty, so it is with our present revolution; had there been no cold war I doubt that we would we be having this meeting now.
It was the human and instrumental view of the Earth and the planets from space that opened our minds and let us see that the Earth was indeed the dynamic system that James Hutton had envisaged more than 200 years ago. We should not forget that the huge lift vehicles that let us first see the Earth from space and that later carried the robot space explorers to Mars, were from the stockpile of ICBMs set aside for war. Whatever the cause we were all filled with wonder by the first ever views of our planet from outside. We owe a debt to NASA for having provided us with the space ships in which to take the steps beyond Darwin and recognise that evolution by natural selection is a property of the whole planet, not just of the organisms alone.
I was recruited by NASA in 1961 only 4 years after the Soviet Sputnik bleeped its cheeky message from space. They said that they needed me for my track record as an inventor of exquisitely sensitive instruments. For the next few years I was engaged in the development of hardware that could withstand the rigors of space and perform when landed on Mars.
But my work was by no means all engineering, the Jet Propulsion Laboratory (JPL) was one of those truly good laboratories that did not segregate its scientists; I soon found myself talking to biologists, physicists and chemists and this is how I was drawn into the design of life detection experiments. Having spent the previous 20 years doing medical research and experimental biology I felt as much at home with the space biologists as with the engineers and chemists.
In January 1965 I was invited to a crucial meeting on life detection for Mars. Before attending I took the precaution of reading that wonderful small book by Erwin Schrodinger What is Life. This book inspired me to ask, “Would it not be easier to look for life on Mars by seeking low entropy as a planetary property than by grubbing around in the regolith looking for organisms?”
When pressed for a way to find low entropy I suggested that a simple atmospheric analysis using a gas chromatograph would do it. A mere nine months later the astronomers at an observatory in France, Pierre and Janine Connes, used a simple telescope equipped with a Fourier Transform spectrometer invented by my colleague Peter Fellgett. The infrared spectra from the telescope provided a near complete analysis of the chemical composition of the atmospheres of Mars and Venus.
The odd and unstable atmosphere we breathe requires the presence at the Earth’s surface of something that can synthesise continuously huge quantities of oxygen and carbon dioxide and also remove equally large quantities of these gases. It is of course the biota; and living organisms must also recycle methane, nitrogen and a number of trace gases. Much more than this the climate is quite sensitive to the abundance of polyatomic gases like methane and CO2 and to the total pressure. These facts in 1965 led me to suggest that some means is needed for regulating the atmospheric composition if the Earth is to remain habitable.
The low entropy of our atmosphere comes mainly from this chemical disequilibrium; it is quite different and should not be confused with the short term physical disequilibria of meteorology. I think the most striking example of the effect of life on the Earth is that despite its greater distance from the Sun, Earth has a higher effective temperature than Venus. It has to have in order to radiate away the excess heat. Perversely adding carbon dioxide lowers the effective temperature of our planet.
The idea of using entropy reduction as a life detection experiment for planets was published in Nature in 1965 and the idea of the Earth as a self-regulating system able to sustain a habitable environment published in the Journal of the American Astronautical Society in 1969.
Because of the novelty the concept and its disconnection from traditional Earth and Life science, I badly needed a succinct and memorable name to encompass the ideas of life, the earth and self-regulation. Sometime in 1969 a near neighbour of mine, the Nobel Prize winning author William Golding who was both a physicist and novelist, suggested that I call this idea ‘Gaia’ after the ancient Greek name for the goddess of the Earth. The first paper with Gaia in the title was given at a Gordon Conference on atmospheric science in 1970 and published in Atmospheric Environment in 1972.
I had by now the bare bones of a hypothesis about our planet as a system that somehow kept its climate and chemistry favourable for life. I knew that life on Earth must be deeply involved but it was not until 1971 that I had the chance to discuss the topic with a distinguished biologist. In that year Lynn Margulis invited me to her lab, then at Boston University, to talk about the role of atmospheric oxygen. We soon began an intense collaboration on the Gaia hypothesis.
Lynn brought to the hypothesis her deep insight as a life scientist, especially the crucial role of microorganisms. I had been trained as a bacteriologist and had worked for nearly ten years on the transfer of infectious diseases. Lynn soon showed me how in the real, the planetary world, human pathogens were almost insignificant and that the Earth had been for billions of years home to microorganisms alone and they still formed its vital infrastructure. It would be fair to say that she put the flesh on the bones of my physiological concept of a living planet. We published joint papers in 1973 one in the Swedish meteorological journal Tellus, expressing my view of Gaia, and the other in Geosciences expressing Lynn’s.
The Gaia Hypothesis was well accepted by atmospheric scientists and to an extent still is but after about 1975 Earth and Life scientists began to attack the concept of life regulating the climate and chemistry of the planet. At first the criticisms were helpful but Neo-Darwinist biologists began what became a polemic and scathing attack on the hypothesis. This was mainly based on their erroneous idea that the hypothesis was anti Darwinian. The talented author and debater Richard Dawkins disputed Gaia with the same vigour he later used about the concept of God.
Prominent Earth scientists also condemned Gaia less forcibly on the grounds that it was not needed to explain the facts of the Earth. These critics led me in 1981 to develop the simple model Daisyworld that showed how an evolving system of plants could regulate the climate of their planet so as to keep it habitable. I am grateful to Andrew Watson for his help in turning this idea into a publishable paper. The model showed that regulation was an emergent property of the whole system Daisyworld not of the daisies alone.
I have enjoyed working on more down to Earth models in collaboration with Andrew Watson, Stephan Harding and Tim Lenton, Lee Kump and James Dyke. This and evidence from the Earth of real mechanisms by which self regulation can happen led me to propose Gaia theory. I am especially grateful to the Geological Society for their open minded generosity towards the concept of Gaia.
So why am I not now just sitting down and listening to what you have to say about our new view of the Earth and the Life upon it? My main reason for not relaxing into contented retirement is that like most of you I am deeply concerned about the probability of massively harmful climate change and the need to do something about it now. I am concerned because the operating system of science has barely changed from that displayed in the courtyard of Burlington House over 100 years ago. Science is still divided into co-existing disciplines each with its own language, journals and forceful defenders. We are tribal animals and such a trait is hard to resist. This may be why the fission of science has been given tenure and made self sustaining by the practice and politics of academic education.
Climate change is likely to be serious and deadly and we may soon need science to be mobilised for the public good as it was at the start of the Second World War. There are signs that this is starting to happen at the institutes of science in the UK and elsewhere. The Royal Society has provided a platform for discussions on the practice of geoengineering and Richard Betts, the director of climate research at the UK’s Hadley Centre, tells me that their planned models for climate projection now include as well as geophysics an active and responsive biota.
I will conclude my talk with a few words about the idea of Snowball Earth, the notion that the Earth was once so cold that it was completely covered by ice, even across the equator. For conservative Earth scientists this is an attractive idea for if there is convincing evidence of a relatively recent snowball it would mean that the Earth system had failed to regulate its temperature. Perhaps then the troublesome idea of Gaia the self regulating Earth would go away.
My excuse for intervening is partly historical. My first visit to Burlington House was in 1954 when I came in evening dress to a Royal Society Conversazione to help demonstrate the successful freeze preservation of living cells, tissues and even whole animals. Then it was a social as well as scientific meeting and part of the London Season. I still remember the delightful ceremony of the occasion as well as the science we displayed.
Cryobiology is concerned with the response of living organisms to cold and freezing and is needed if we are to understand snowballs Earth. At present the evidence and models that go to explain past super glaciations tend to come from geological science alone and assume that life on Earth is a passive victim of the frigidity and quite unable to resist actively still less to be the cause.
Organisms are not usually happy in the frozen state and contrary to common perception this has little to do with the cold or with crushing or spearing by ice crystals. Freezing is harmful because it removes water from the Earth system as ice. Because ice is a pure substance, solutes are left behind and the ocean concentrates. Once the ocean salinity increases from 0.6M, to 0.8 Molar a lethal event occurs, especially with eukaryotes, the internal and external lipoprotein membranes of their cells dissolve. The maximum salinity that is compatible with main stream multicellular life is 0.8 Molar and above this the weak Van der Waals forces holding cell membranes intact are insufficient to prevent dissolution and death.
If the ocean temperature cooled to -3C or below, many eukaryotes would die. Exceptions would include a few oddities such as brine shrimps that have shells so impermeable that they keep their internal salinity the same as ours. Specialised halophile bacteria also exist and can live in almost saturated brine. But an ecological revolution this large would surely have left its mark on the fossil record. To reach the critical salinity of 0.8M requires the freezing of 25 % of the ocean’s water. Where would the ice be? In a glaciation water first freezes out from the vapour phase as snow on mountains and on the surface of Polar Regions but whenever and wherever ice forms the ocean grows more saline.
What may have happened is that newly evolved eukaryotes experienced increased salinity from drying, especially when left on the beach by the tide. Selection favoured those able to synthesize substances that protected against high salinities. Neutral solutes, like glycerol or sugars were synthesised or more effectively charge neutral salts such as the sulphur and nitrogen betaines.
After their use in cryoprotection these compounds break down and release as vapours dimethyl sulphide (DMS) and as Peter Liss discovered, methylated ammonias. In the air DMS oxidises rapidly and the products combine with the amines to form cloud condensation nuclei and so lead to more and denser clouds and a cooler climate. In 1987 Charlson, Andreae, Warren and I published a Nature paper suggesting that this phenomenon serve in the natural climate regulation of the Earth System. This has been partially confirmed as real in the Southern Hemisphere by Simo and colleagues but so far sulphur pollution in the Northern Hemisphere is so great that the effect has not yet been discerned.
The total consequences of the changes can be beneficial, neutral or harmful. This way the sensitivity of eukaryotes to salinity also may offer a biological explanation of the cause of neo-proterozoic glaciations. I ask you to consider the possibility that a massive production of DMS occurred as a response to increasing salinity as ice formed in the early part of a neoproterozoic glaciation.
This would have led to a strong positive feedback on cooling and a move to the ice house. Eventually with increasing ice cover and lower temperatures DMS production would decrease and the feedback on cooling stop. More important other organisms would evolve to feed on the surplus of DMSP and DMS in the ocean so that in time only 0.1% of the total production DMS escapes from the ocean to the atmosphere as it does now and temperatures would rise again.
The Huronian glaciations of the period more than 2 billion years ago were at a time when the Earth was inhabited by prokaryotes only, these are well known to be resistant to freezing and drying and will often form even more resistant spore bodies from which live organisms can be recovered by adding water.
This brief speculation about Snowballs Earth arose in conversations with the ocean scientist, Brian von Herzen in 2009. We have no notion if it offers a correct explanation but I put it to you as an example of the need for a whole science approach when seeking explanations of planetary scale phenomenon on a live planet like the Earth. This is especially true of the next catastrophe, the climate change we are now causing by the excessive excretion of CO2.
Catastrophe does not have to be physical and external; it can come from the failure or reversal of an internal feed back and be biologically driven. Mistakes can happen as may have happened when the photosynthesisers first appeared and released oxygen which was then a potentially toxic gas. There are no benign or malign organisms: we just do our things and suffer or enjoy the consequences. I like to think our CO2 emissions were an innocent mistake not something done with malice, so there is no occasion to feel guilty about it.
The remaining life span of the biosphere is unlikely to be much more than 500 million years, so that if humans died out the chances of our replacement by another intelligent communicating species is improbable. If this is true then we have a goal a purpose. As part of the Earth system our job is to help keep our planet habitable and perhaps become a step in the evolution of an intelligent planet.