The Proterozoic Eon. CHAPTER 7. Proterozoic- Last chapter of Precambrian time. The Proterozoic boundary is placed @ 2.5 By, mostly arbitrarily Essentially modern plate tectonic activity Archean cratons provide basis for continental development and attachment (accretion)
The Proterozoic boundary is placed @ 2.5 By, mostly arbitrarily
The Midcontinent Rift and the Keweenawan Sequence
Figure 7-8 (p. 247) Rift and Grenville Province.The Neoproterozoic supercontinent Rodinia as it began to break apart. (After Hoffman, P. F. 1991. Science 252: 1409-1412.)
Microfossils of the Gunflint Chert
Photomicrograph of spheroidal and filamentous microfossils from the Gunflint Chert of Ontario Canada
Eukaryotes are thought to have arisen from an originally endosymbiotic relationship between two or more prokaryotic cells.
Doushantuo Formation Metazoans--Eggs & Embryos
Tribrachidium heraldicum, a possible primitive echinoderm or cnidarian
Spriggina floundersi, a possible ancestor of trilobites
Figure 7-32 (p. 261 the Grand Canyon of the Colorado River.)Reconstruction of Kimberella.(After Fedonkin, M. A., and Waggoner, B. M. 1997. The Late Precambrian fossil Kimbrella is a mollusk-like bilateral organism. Nature 388(28): 868-871).
Geologic time scale across the Precambrian-Cambrian boundary, showing the Vendian, and indicating the occurrence of the Ediacaran fauna, the small shelly fauna (first known hard parts),