Geology 1 Chapter 1

1. Geology 1Chapter 1 5 3 2 1 0 • Objectives: • Describe the components of the Earth as a system. • Explain how the Earth works. 4

2. What sets them apart…

3. Some important observations and their implications Carbon dioxide dominates the atmospheres of Venus and Mars. Hydrogen and helium dominate the atmospheres of Saturn and Neptune. Nitrogen and oxygen dominate Earth’s atmosphere. Oxygen and methane coexist in the Earth’s atmosphere, and these are continuously consumed and replaced. The Earth, alone among the planets, had a carbon-based life and an industrial civilization. The Earth is a living planet, and whoever or whatever is living there is not wise.

4. No, I’m not the stupid inhabitant referred to in the previous slide, but I have two questions for you guys… What’s keeping Earth’s chemically unstable atmosphere “constant” and so appropriate for life? What kept the climate tolerable despite a 30% increase in solar luminosity (=R2T4) since the Earth formed?

6. The Gaia Theoryidea by James E. Lovelock and Lynn Margulis; name proposed by William Golding “Organisms and their material environment evolve as asingle coupled system, from which emerges the sustained self-regulation of climate and chemistry at a habitable state forwhatever is the current biota.” Daisyworld: a model of dark- and light-colored plants that competed for growth on a planet in progressively increasing sunlight. Not a blueprint for the Earth, but a model to show that the Gaia theory is consistent with natural selection. This "Daisyworld" regulates its temperature close to that fittest forplant growth. It is stable, insensitive to initial conditions and resistant to perturbation.

7. Cows and daisies ? Negative feedback = mechanisms that act to counteract the initial change so as to maintain the status quo Positive feedback = initial change is amplified by subsequent processes

8. Critics however say… Daisies would adapt to changing temperature and therefore simply track temperature change, not regulate it; self-regulation is not necessarily a consequence of feedback mechanisms. Global self-regulation could never have evolved, as the organism was the unit of selection, not the biosphere. How can self-regulation at the planetary level emerge from natural selection at the individual level? Life plays a role, but not the main one, in the evolution of the physical environment.

9. Conjectures and refutations CON: Biological processes regulate atmosphere compositions. REF: 2% acceleration of carbon uptake by biosphere vs. 35% rise in atmospheric CO2 since pre-industrial times. CON: Terrestrial ecosystem (biotic) carbon uptake more sensitive than ocean (abiotic) uptake. REF: Both processes are equally insensitive. CON: Biological by-products in the atmosphere should act as planetary climate regulators. REF: Vostok ice cores indicate that CO2, CH4 and dimethyl sulfide function to make the Earth warmer when it is warm, and colder when it is cold.

10. More conjectures and refutations CON: Biological feedbacks should regulate Earth’s climate over the long term. REF: Peaks in paleotemperature corresponds to peaks in paleo-CO2 in records stretching back to the Permian (i.e. more than 300 m.y.). CON: Organisms alter the environment to their own benefit. REF: Nutrient depletion by planktons in oceans has almost created a biological desert. Apparently, where organisms enhance the environment for themselves, they create positive feedback. Therefore, Gaia theory’s two central principles are mutually inconsistent with one another.

11. Some recent results Postdam Institute for Climate Impact Research, Germany (1997) Model biosphere is able to control, via local interactions of competing species, almost perfectly the geophysical conditions (e.g., global temperature) for its own existence. If the environmental stress exceeds certain thresholds, however, life breaks down on the artificial planet via a first-order phase transition, i.e., in a non-reversible way. There is a close connection between self-stabilizing capacity, biodiversity and geometry of habitat fragmentation. Unrestricted Darwinian competition, which reduces the number of co-existing species, is the best guarantee for survival of the artificial ecosphere as a whole.

12. Why is the Gaia Theory so important? Reconciles current thinking in evolutionary biology with that in evolutionary geology. Extends, not contradicts, Darwin's vision, just as relativity enhances, not denies, Newtonian physics. Although provisional, the theory provides an intellectual habitat where understanding of the Earth can evolve and grow. Its greatest value lies in its metaphor of a living Earth, which reminds us that we are part of it and that human rights are constrained by the needs of our planetary partners.

13. References/Sources of materials Animations from www.animationlibrary.com On the Gaia Theory: Kirchner, J.W., 2003. The Gaia hypothesis: Conjectures and refutations. Climate Change 58, 21-45. Lenton, T.M., 1998. Gaia and natural selection. Nature 394, 439-447. Lovelock, J.E., 2003. Gaia: the living Earth. Nature 426, 769-770. Van Andel, T. H., 1994. New views on an old planet: A history of global change. Cambridge University Press, 402 p. Example of geophysiological modelling: http://www.pik-potsdam.de/~bloh/ Photos of the Darwin Spacecraft model and interferometry simulation: http://ast.star.rl.ac.uk/darwin/ Planetary atmosphere vital statistics: http://nssdc.gsfc.nasa.gov/planetary/factsheet/