Fossils and the Discovery of Earth History

Fossils and the Discovery of Earth History

Lecture 004

FOSSIL

Evidence of the existence of past life

Problems with using fossils:1. only organisms with hard parts will be

fossilized and leave a record2. if you find a fossil in a certain place, it

doesn’t mean it lived there; example-continent moved after extinction

3. record is uneven in time and area4. many fossils that get preserved are a

dead end5. most of record is lost or unexplored;

missing link- look at homonids

Benefits of using fossils:

1. provides evidence that it once existed

2. provides minimum ages

3. documents extinction’s

4. use them to put together scenarios in paleoclimatology or extinction/immigration scenarios-----complete record with Hyracotherium

Horse Evolution

Horse Evolution Timeline

Hyracotherium

55 myaEOCENE ERA

Mesohippus

40 myaOLIGOCENE ERA

Miohippus

30 myaOLIGOCENE ERA

Merychippus

20 myaOLIGOCENE ERA

Pliohippus

10 myaOLIGOCENE ERA

Equus

4 myaMODERN ERA

Hyracotherium55 mya

Miohippus35 mya

Merychippus17 mya

Equusmodern

Note: diagram is scaled so organisms appear to be the same size

TYPES OF FOSSILS

Body Fossils Remains of the organism itself

Trace FossilsEvidence of the movement or activity of

the organism

Body Fossils

stingray

fish

TRACE FOSSILS

Tracks and TrailsBurrows and Borings

Coprolites

Trace FossilsTracks Trails

Trace FossilsBurrows & Borings

This section of fossil conifer wood is Cretaceous of the Antarctic Peninsula.The round holes, filled with brown mudstone or white crystals, were formed by wood-boring bivalves that bored into the log while it was floating on the Cretaceous seas as driftwood.

CoproliteCoprolite

Trace Fossils

Modes of Body Part Preservation

1. Unaltered fossils• Soft parts (rare) & Hard parts

A. peat bogsB. amber C. tar pits D. mummification or desiccation E. refrigeration

Jellyfish fossil- Precambrian Edicarian Fauna

Modes of Body Part Preservation

2. Altered fossils• petrifaction

permineralizationreplacementrecrystalization

• carbonization

Modes of Body Part Preservation

3. Imprints• molds• impressions

1. Unaltered FossilA. Peat bog

A variety of fossils preserved by rapid burial in this anaerobic environment.

Amber is the pitch from conifer trees

1. Unaltered Fossil B. Amber With Insects

Mosquito in AmberMosquito in Amber

1. Unaltered FossilC. Tar Pits

La Brea Tar PitGround Sloth

1. Unaltered Fossil D. Mummification

LeonardoDuck-billed dinosaur

77 myo. Montana

Wooly Mammoth frozen in Siberia(found 1987)- 20,000 years old

1. Unaltered FossilE. Refrigeration

2. Altered FossilPetrifactionPermineralized- original pore space is filled in with minerals

Shark’s Tooth

2. Altered FossilPetrified wood

coal

2. Altered FossilCarbonization

3. Imprints

Glossopteris impression

Gastropod mold

Other Kinds of Evidence For Past Life

GastrolithsFossil Fuels

• Fossils exhibit great diversity in forms, some resembling living forms, some appearing very different from modern forms.

• Physical consistency is usually that of stone rather than of the materials exhibited by comparable living species.

• Many fossils are found high in the mountains resembled forms that normally occur in the ocean.

• Fossils are often found encased in hard stone.

Characteristics of Fossils Known to the Ancients

• 80,000 year old Neanderthal site with fossil snail and coral skeletons.

• 35,000 year old Cro-Magnon burial site with fossil-shell necklaces.

• Early Egyptian site (perhaps 3200 B.C.E.) with fossil mounted in metal.

• It is possible, but not certain, that these prehistoric peoples regarded fossils as magical.

Evidence for Early Human Interest in Fossils

Mythical Ideas About FossilsMythical Ideas About Fossils

Fossils grew in the rocksNo distinction between fossils and crystals and oresMagical and curative powers Artifacts of the Devil

155 - 222 C.E.Tertuillian

The view that great floods were a major contributor to earth evolutionExample of catastrophism

Leonardo da VinciLeonardo da Vinci

1452 - 1519

• Observed fossils on mountains• Rejected flood theory• Argued that the earth is old• Grasp concept of superposition

Petrified Wood

Studied fossils and compared them to living organisms

Robert Hooke (1635-1703)

Nicholaus StenoNicholaus Steno

1638 - 1686Compared sharks teeth to “tongue stones”Argued that fossils could be altered in chemical composition without changing their formSteno’s Law of Superposition

SuperpositionSuperposition

SuperpositionSuperposition

Stratigraphic setting of the Cambrian Burgess Shale

540 MYA

505 MYA

Georges-Louis Leclerc de BuffonGeorges-Louis Leclerc de Buffon

1707 - 1788

Origin of the Earth- collision of a comet with the sunAge of Earth ~75K

Histoire Naturelle

Baron Georges CuvierBaron Georges Cuvier

1769 - 1832

CatastrophistSpecies don’t change over timeTheory of extinction

• Fossil record provided evidence for catastrophes

• Earth is young• E.g. Noah’s flood• Recent: meteor impact &

volcanism

William SmithWilliam Smith

Development of the Geologic Time ScalePrinciple of faunal succession

1769 - 1839

Correlating Rock Layers

James Hutton

• The Rock Cycle

• Deep Time

• Uniformitarianism

1726 - 1797

The Rock CycleThe Rock Cycle

Deep TimeDeep Time

"we find no vestige of a beginning and no

prospect of an end"

UniformitarianismUniformitarianism

• The present-day earth has been shaped slowly by everyday forces of erosion and deposition

• Earth is old

• E.g., erosion & uplifting = mountains

Charles LyellCharles Lyell

1797 - 18751797 - 18751797 - 18751797 - 1875

Percentages of TertiarySpecies Still Living

Recent Pliocene

Older Pliocene

Miocene

Eocene

96

42

17

3

CATASTROPHISM

VERSUS

UNIFORMITARIANISM

• The earth's surface has been shaped by the cumulative effects of episodic events over long periods of time.

• Some may have been catastrophic, resulting in mass extinctions.

• The geologic evidence was not consistent with the theory of catastrophic global floods

• The earth is ancient, far longer than the 6,000 years provided by a literal reading of the Bible.

Catastrophism vs. UniformitarianismResolution

Questions:

• Jellyfish are not often seen in the fossil record because:

• The shark’s tooth is an example of an altered fossil that underwent _________.

• Stenos Law of Superposition stated that:• Evidence to support catastrophism included:• Leonardo da Vinci theorized that shells found

on a mountain top got there because _____________.