"We can only understand macroevolution - the comings and goings of species and higher taxa through time - if we link the microevolutionary processes studied by geneticists with Earth's dynamic environmental history."- Knoll, 2003 , Life on a Young Planet.
Evidence for evolution is often taught using the fossil record and biogeography whereas the mechanisms of evolution are generally taught from a genetic and molecular/cell biology perspective. Taught together, modern biology and Earth history can be used to teach a well-rounded basic unit on evolution or to deal with particular important and problematic topics such as:
- The origin of life: We're eager to learn how life formed on the early Earth, because we are now searching for extraterrestrial life and trying to decide what kinds of worlds to look at. How the first cells formed is purely hypothetical at this stage, but the hypotheses depend greatly on what geology can tell us about the Earth's early atmosphere, the chemistry (and stability!) of the oceans. How early? We're not sure, but the search for the earliest fossils and biomarkers continues.
- Taxonomy: Modern taxonomists are working out lineages and revising older taxonomies by combining information on the morphological characters of living species within a group and their extinct fossil relatives with genetic information on the living species. Without the data from fossils, it is impossible to work out consistent relationships among many living species. Interestingly, many taxonomists are primarily stratigraphers, working to correctly identify index fossils in order to work out accurate stratigraphic relationships.
- Rates and mechanisms of speciation and extinction: Estimations of past biodiversity and changes in rates of appearance and disappearance of taxa from the fossil record help us understand the processes of speciation and extinction. This information in turn is invaluable for determining the extent of the current biodiversity crisis. Taxonomic training is also important for this project.
- Human evolution and the question of race: Recent molecular studies indicate that modern humans have a recent common ancestor and that this person is likely to have lived in Africa. However, the "Out-of-Africa" theory is also based on the distribution of fossil human remains controversial. A New Perspective on Race
The above list is by no means complete.
As evolution is a very broad topic, a variety of different courses on the subject will use Earth history in different ways.
- One of the most familiar is Invertebrate Paleontology, since many invertebrate lineages have excellent fossil records.
- An Earth history approach has also become a valuable tool for studying Biogeography.
See also the Mechanisms of Evolution Links
Below are web resources relevant to the specific subjects described above.Astrobiology
- NASA Astrobiology Institute (NAI). This site provides information on NAI research, a library of publications, sections for teachers and students, and an Ask An Expert section. The student section features Astro-Venture, where students can search for and build a habitable planet; Habitable Worlds, to search the solar system for planets that might support life; and Mysteries of Microbes, containing videos and biographies of astrobiologists. The teacher section contains an astrobiology-related resource catalog of NASA sites. (more info)
- The Astrobiology Web. This site contains astrobiology news and links about: astrochemistry, bioinformatics, biosatellites, gravitational biology, hydrothermal vent communities, genomics, astropaleobiology, radiation physiology, the search for exterrestrial intelligence (SETI), extremophiles, exopaleontology, cell biology, evolution, planetary protection, and space medicine. There are also links to NASA TV and video feeds, astrobiology press releases, and an introduction to what an astrobiologist is. (more info)
- Changing Paleoclimates and Mass Extinctions (more info) This article provides a model for climatic change and relates climatic cycles with major extinction events in the history of the Earth. It discusses the mechanisms behind modern climate zones (circulation, storm systems, seasons), astronomical models, climatic models (obliquity conditions, rising sea levels, current conditions), and mass extinctions and model timing (causes of extinction events, predicted vs. documented extinctions, and extinction-driven evolution). A geologic time scale provides a reference for climatic conditions at different periods in Earth history. References are provided for additional information.
- Extinction: Forest Fires Among the Trees of Life (more info) This outline of a presentation on extinction reviews the various catastrophic events that could lead to extinction and lists the five great mass extinctions. Climate change is identified as the linking factor and recovery is also explained.
- Tracking the Course of Evolution: Extinction (more info) This essay on mass extinction events (Ordovician, Devonian, Permian, Triassic, Cretaceous) in the geologic record is a chapter from History of Life, a book written by Richard Cowen, in which he discusses the general geologic body of knowledge surrounding each mass extinction event. Additionally, the author provides thirty-two (32) bibliographic references (primarily peer-reviewed science journals) on these mass extinction events.
- Understanding Evolution From the University of California Museum of Paleontology at Berkeley, this site includes links to Evolution 101 which features extensive information on evolution, K-16 teaching materials, a resource library, and news articles and highlights.