This description of the fossil record of bacteria focuses on one particular group of bacteria, the cyanobacteria or blue-green algae, which have left a fossil record that extends far back into the Precambrian. The oldest cyanobacteria-like fossils known are nearly 3.5 billion years old and are among the oldest fossils currently known. Cyanobacteria are larger than most bacteria and may secrete a thick ... Full description.

Information on this page pertains to dinoflagellates, the fossil record of which may extend into the Precambrian. Spherical organic-walled microfossils known as acritarchs, some of which may be dinoflagellate hystrichospheres, first appear in rocks about 1.8 billion years old. Exactly what the acritarchs were is not known with certainty; they probably included a number of clades of eukaryotic algae, ... Full description.

This site describes some unusual fossils of the late Precambrian age, found on exposed rock surfaces along the southern coast of the Avalon Peninsula in Newfoundland. The most famous locality where these fossils can be seen is at Mistaken Point at the southernmost tip of the Avalon Peninsula. The Mistaken Point fossils were preserved by being blanketed with layers of fine volcanic ash and are dated ... Full description.

This site describes the White Mountains, the Inyo Mountains, and associated ranges along the California-Nevada border north of Death Valley. This location presents one of the most important and best-known Late Proterozoic to Cambrian sections in the United States. Starting with the unfossiliferous Precambrian rocks of the Wyman Formation, paleontologists can work their way through a complete section ... Full description.

The Tommotian Age began about 530 million years ago and is a subdivision of the early Cambrian. Named for rock exposures in Siberia, the Tommotian saw the first major radiation of the animals, or metazoans, including the first appearance of a great many mineralized taxa such as brachiopods, trilobites, archaeocyathids, molluscs, and echinoderms. A few million years before the Tommotian, in the Vendian, ... Full description.

This site describes the Cambrian fossil record, which indicates a distinct development from simple organisms to organisms comparable in morphology and organization to present-day animals. The development is documented by faunal assemblages represented by the Ediacara fauna, the first complex trace fossils, the earliest shelly faunas, and the onset of the typical Cambrian macrofaunas. This rapid evolution ... Full description.

This site describes the fossils in the Stephen Formation near the Burgess Pass in present-day Yoho National Park, British Columbia, known today as the Burgess Shale. More than 65,000 specimens have been collected from the dark shale, many of which have partially or entirely preserved soft-parts that provide a unique window to Cambrian and Early Paleozoic biota. The fossiliferous strata of the Burgess ... Full description.

This site describes the Chengjiang fauna, one of the most exciting, oldest, and best preserved Paleozoic biota. With a wealth of different taxa that was never expected for the Early Cambrian, it is said to be the most spectacular paleontologic discovery since the Burgess Shale of British Columbia and one of the most important fossil archives known so far. After information on stratigraphy and preservation, ... Full description.

This site describes the Silurian period, a time during which the Earth underwent considerable changes that had important repercussions for the environment and life within it. The stratigraphy link describes the subdivisions of the period into four epochs. Each epoch is distinguished from the others by the appearance of new species of graptolites. Two other links lead to a detailed discussion of life ... Full description.

This lesson will clarify the development of the geologic time scale. It will also introduce students to the major time periods in the history of Earth, as well as to the role fossils play in helping us understand this history. This lesson is based on an online booklet that provides an introduction to the study of the history of Earth, published by the U.S. Geological Survey. Using careful analogies ... Full description.