Index Fossils, Evolution, Biostratigraphy and the Geologic Time Scale

Bio-Events

First appearances of new species First appearances of new higher taxa Extinctions of species Mass extinctions of multiple taxa Bio-events are unique points in geologic

time

Index Fossils

Some fossils are more useful than others for relative age determinations

Fossils that are most useful are called INDEX FOSSILS

What factors would maximize a fossil’s usefulness?

Index Fossils

Limited Stratigraphic Range Widespread Geographic

Distribution Commonly Pelagic Or, tolerant of a wide variety of

environments (found in many facies)

Geologic Time Scale

Standard subdivisions of Earth’s history A “common language” by international

agreement Bio-Events are used to subdivide Geologic Time Stratotypes or “type examples” are designated

so comparisons can be standardized

Geologic Time Scale

A hierarchy of time units Eon

Era Period

Epoch Age

Boundaries are defined by bio-events

Eons

Phanerozoic – “obvious life” – 530 Ma to present Proterozoic – “prototypical life” – 2.5 Ga to 530 Ma Archean – “ancient” – circa 4.6 Ga to 2.5 Ga Archean and Proterozoic comprise nearly 90% of

Earth’s history!

Phanerozoic Eon

Cenozoic Era – “modern life” – 65 Ma to present Mesozoic Era – “middle life” – 248 Ma to 65 Ma Paleozoic Era – “ancient life” – 543 Ma to 248 Ma

Learn the following (in order from oldest to youngest):

3 Eons 3 Eras of the Phanerozoic All of the Periods of the Phanerozoic and the

Eras to which they belong “Picks” – numerical ages of the boundaries

between Eons and between Eras

Index Fossils andInternational Stratotypes

Biostratigraphy and Global Politics

Systems, Series, Stages Devonian System

Upper Devonian Series Famennian Frasnian

Middle Devonian Series Givetian Eifelian

Lower Devonian Emsian Pragian Lochkovian

Silurian System Upper Silurian Series

Přídolí Stage

Index Fossilsand the S-D Boundary

Graptolites * Conodonts * Chitinozoans * Trilobites Brachiopods Cephalopods

Definition ofthe S-D Boundary

Stratotype: Klonk, near Suchomasty, Czech Republic

S-D GSSP

GSSP = Global Stratotype, Sequence and Point

First appearance of Monograptus uniformis uniformis

Bed 20 Klonk, Czechia