Summary

The following summarizes some themes that ran through the course. We didn’t necessarily express these generalities in exactly this way, but I think you’ll recognize the essence.

From a high enough perspective, the history of life is a story about:

1) the origin of major new innovations in adaptation, such as the origin of cells with organelles and a nucleus (protists), the origin of multicellular life (plants, animals, fungi), and the origin of major groups within these such as animal phyla. Most of the major groups appeared by 500 million years ago.

2) the diversification and extinction of life, in numbers of species, what we call “biodiversity”; biodiversity climbs and plummets throughout Earth history, though there seems to have been a net gain through time

One well-known plot shows the global diversity of life in marine settings through time. This data is one basis for our understanding of the three marine faunas through time (Cambrian, Paleozoic, and modern) and the five large mass extinctions.

3) the expansion of life into new habitats; generally, this seems to have increased continually through time, and includes conquest of the land in the Paleozoic Era, conquest of the air in the late Paleozoic and Mesozoic Eras, conquest of the deep sea, and other extreme environments

4) life “re-discovers” solutions to adaptation to certain conditions, so that quite unrelated animals share certain features;

· birds, bats, & pterosaurs all have adapted to flying via wings in various ways;

· brachiopods, clams, and other aquatic invertebrates use two valves (shells)

· ichthyosaurs, plesiosaurs, mosasaurs, and whales all adapted to water, evolving from land-vertebrates; each has some features in common and different with each other and with fish

There are a few generalities about the study of paleontology too.

1) Paleontology is the only record of the chronicle of ancient life. Though we can understand relationships among living animals by comparing the anatomy and genetics of living animals, one can only understand the actual history of life through fossils. Usually, both kinds of information are helpful for understanding the whole picture.

2) What we know about the past is based in part on what we know about the present. Inferences about everything from how an animal looked to behavior and ecology come in part from study of modern organisms. We also make estimates about the past based on an understanding of physical principles of how things work – for example, studying the way an animal probably moved given the shape of its skeleton, even if we have no exact modern analogs.

3) Paleontology and geology are historical sciences. Events cannot be literally repeated, but multiple forms of independent evidence can used to try to explain past events (confluence of evidence), and these forms of evidence are based on understanding of natural processes that can be repeated in modern settings (laboratories or in nature). For example, we can look for many different kinds of evidence that an extraterrestrial object hit the Earth at the Cretaceous-Tertiary boundary; the science is in testing whether the predictions of what we should find if an impact occurred turn out to be correct or not, based on the evidence we find in rocks of that age.