Fossils Lecture 1

Geologic Time Scale From largest to smallest: Eon, Era, Period, Epoch, Age There is also an even larger section called a supereon. However, we do not care about this one as there is only one: the Precambrian We will also not be too concerned with memorizing epochs and ages There are 4 eons (from oldest to most recent): the Hadean, the Archean, the Proterozoic and the Phanerozoic The Hadean, Archean and Proterozoic are part of the Precambrian, we won’t worry about these too much for now.

Precambrian (4500-450 mya) Very little is known about this supereon because lifeforms in this time lacked hard shells or skeletons We have found fossils that we call stromatolites that show indications of the presence of cyanobacteria. These were first found in the Archaean Eon. The first evidence of life probably first emerged mid-Hadean

Phanerozoic (540 mya-present) Shelled invertebrates first begin to emerge during the Phanerozoic Eon, as such we have a much better understanding of lifeforms during this time This Eon is divided into 3 Eras (oldest to most recent): Paleozoic, Mesozoic, Cenozoic Each era was dominated by different types of animals

Paleozoic (542-248mya) Name refers to “ancient animals” as the age was dominated by marine invertebrates Divided into 6 periods Cambrian and Ordovician Periods – marine invertebrates emerge along with primitive fish. These two periods form the “age of invertebrates” MASS EXTINCTION EVENT Silurian and Devonian – Early land animals and amphibians emerge as well as forests. These periods form the “age of fishes” Carboniferous – Further divided into Mississippian and Pennsylvanian periods. Shallow seas and coal bearing rocks form in the two periods respectively Permian – Earliest gymnosperms or cone-bearing trees begin to form. Together with the Carboniferous period forms the “age of amphibians”

Mesozoic (251.1-65.5 mya) Dinosaurs!!! More boringly “the Age of Reptiles” Triassic Period – First dinosaurs and the earliest mammals emerge MASS EXTINCTION EVENT Jurassic Period – Earliest birds Cretaceous Period – Flowering plants develop. This is where all the cool looking dinosaurs emerge.

Cenozoic (65.5mya-present) Divided into 2 Periods: Tertiary and Quaternary The Tertiary period is further divided into the Paleogene and Neogene periods (as seen on your sheet) The Cenozoic differs from previous eras because the periods can further be divided into Epochs

Tertiary (65.5-1.8 mya) Divided into 5 epochs that we won’t be going into specifically Apes, birds and grazing animals develop. Like REALLY big birds. The first modern animals develop near the end of this period.

Quaternary (1.8mya to present) This is where humans first emerge Divided into epochs that we also don’t really care about differentiating We are in the: Phanerozoic Eon Cenozoic Era Quaternary Period Holocene Epoch