Biodiversity over Time 1.1 2004/05/28 11:23:12 GMT-5 2004/07/13 14:08:59.892 GMT-5 Robert Ahlfinger ahlfing@rice.edu Robert Ahlfinger ahlfing@rice.edu The history of life on Earth is described in various publications and web sites (e.g., Speer, B.R. and A.G. Collins. 2000; Tudge, 2000; Lecointre and Guyader, 2001; Maddison, 2001 Eldredge, 2002); it is also discussed in the module on Macroevolution: essentials of systematics and taxonomy. For the current purpose of understanding what is biodiversity, it is only necessary to note that that the diversity of species, ecosystems and landscapes that surround us today are the product of perhaps 3.7 billion (i.e., 3.79 ) to 3.85 billion years of evolution of life on Earth (Mojzsis et al., 1996; Fedo and Whitehouse, 2002). Thus, the evolutionary history of Earth has physically and biologically shaped our contemporary environment. As noted in the section on Biogeography, plate tectonics and the evolution of continents and ocean basins have been instrumental in directing the evolution and distribution of the Earth's biota. However, the physical environment has also been extensively modified by these biota. Many existing landscapes are based on the remains of earlier life forms. For example, some existing large rock formations are the remains of ancient reefs formed 360 to 440 million years ago by communities of algae and invertebrates (Veron, 2000). Very old communities of subterranean bacteria may have been responsible for shaping many geological processes during the history of the Earth, such as the conversion of minerals from one form to another, and the erosion of rocks (Fredrickson and Onstott, 1996). The evolution of photosynthetic bacteria, sometime between 3.5 and 2.75 million years ago Schopf, 1993; Brasier et al., 2002; Hayes, 2002), played an important role in the evolution of the Earth's atmosphere. These bacteria released oxygen into the atmosphere, changing it's composition from the former composition of mainly carbon dioxide, with other gases such as nitrogen, carbon monoxide, methane, hydrogen and sulphur gases present in smaller quantities. It probably took over 2 billion years for the oxygen concentration to reach the level it is today (Hayes, 2002), but the process of oxygenation of the atmosphere led to important evolutionary changes in organisms so that they could utilize oxygen for metabolism. The rise of animal and plant life on land was associated with the development of an oxygen rich atmosphere. Brasier, M.D., O.W. Green, A.P. Jephcoat, A.K. Kleppe, M.J. Van Kranendonk, J.F. Lindsay, A. Steele, and N.V. Grassineau. Questioning the evidence for Earth's oldest fossils Nature 2002 416 76-81 Eldredge, N Life on Earth. Volumes 1 and 2 ABC Clio 2002 Santa Barbara, California, U.S.A. Fedo, C.M. and M.J. Whitehouse Metasomatic origin of quartz-pyroxene rock, Akilia, Greenland, and it's implications for Earth's earliest life> Science 2002 296 448-1452 Fredrickson, J.K. and T.C. Onstott. Microbes deep inside the Earth Scientific American. 1996 68-73. Hayes, J.M. A lowdown on oxygen Nature 2002 417 127-128 Lecointre, G. and H. Le Guyader Classification phylogenetique du vivant Belin 2001 Paris, France Maddison, D.R The Tree of Life Web project. D.R. Maddison, editor http://beta.tolweb.org/tree (accessed August 20, 2003) Mojzsis, S.J., G. Arrhenius, K.D. McKeegan, T.M. Harrison, A.P. Nutman, and C.R.L. Friend Evidence for life on Earth before 3,800 million years ago Nature 1996 403 853-858 Schopf, J.W Microfossils of the Early Archean Apex Chert: new evidence of the antiquity of life. Science 1993 260 640-646 Speer, B.R. and A.G. Collins University of California Museum of Paleontology Taxon Lift 2000 http://www.ucmp.berkeley.edu/help/taxaform.html (accessed August 20, 2003) Tudge, C The variety of life. Oxford University Press 2000 Oxford, U.K. Veron. J Corals of the World. Australian Institute of Marine Science and CRR Qld Pty Ltd. 2000 Townsville MC, Queensland, Australia.