A trip through geologic time:Fossils

Uniformitarianism

• The present is the key to the past.• The same geologic processes that operate

today operated in the past

Fossil fish- not a goldfish

Fossils: evidence of past life

Fossil Formation:1. organism dies2. organism buried in sediment 3. sediments slowly harden into

rock preserving the parts of the organism

Most important conditions for fossil formation

• Rapid burial• Hard parts

Types of Fossils

Mold and Cast1.organism dies, gets buried, decomposes – leaves behind a hole the shape of the original organism ( the mold)2.Water washes in sediments which fill in the mold and solidify to form a rock with the same external structure as the organism had (the cast)

Trilobite fossil

• Petrified: (mineralized) fossils- organism dies, every molecule of the organism is replaced by a molecule of a mineral

• This shows the internal structure as well as the external structure.

Petrified Wood

Actual Fossils

The actual organism frozen in ice or amber (tree sap)

Termites in amber

Frog in amber

Baby mammoth frozen in ice

Trace Fossils:evidence that an organism has been there

coprolyteDinosaur footprint

gastroliths

Dinosaur tracks

Worm casings

Carbon films: an extremely thin coating of carbon on rock

Leaf fossil

Index Fossil: fossils of widely distributed organisms that lived during

only one short period.

http://cartage.org.lb/en/themes/sciences/Paleontology/FossilsAndFossilisation/AmberFossils/AmberFossils/AmberFossils.htm

http://news.bbc.co.uk/2/hi/6284214.stm

http://www.envs.emory.edu/faculty/MARTIN/ichnology/tf-eggs.htm

http://en.wikipedia.org/wiki/Gastrolith

http://www.clas.ufl.edu/users/pciesiel/gly3603c/fossils.html

http://pubs.usgs.gov/gip/geotime/fossils.html

Picture bibliography