5-2 The Fossil Record

http://www.kpbsd.k12.ak.us/chapman/demers/images/collage2.JPG

What is a fossil?What is a fossil?

• Some of the most important clues to Some of the most important clues to Earth’s past are fossils.Earth’s past are fossils.

• A fossil is the preserved remains or A fossil is the preserved remains or traces of an organism that lived in traces of an organism that lived in the past.the past.

• Most fossils form when organisms Most fossils form when organisms that die become buried in sediments that die become buried in sediments (particles of soil and rock).(particles of soil and rock).

Why are fossils important?Why are fossils important?

• It enabled scientists to see occurrence of It enabled scientists to see occurrence of extinction in different speciesextinction in different species

• It gave Darwin evidence that earth is older It gave Darwin evidence that earth is older than previously believed and that very than previously believed and that very slow changes over a long period of time slow changes over a long period of time can add up to substantial changes in can add up to substantial changes in organismsorganisms

• It shows evidence of continental drift – the It shows evidence of continental drift – the belief that the continents were once one belief that the continents were once one large landmasslarge landmass

Plummer et al 2003

FossilizationFossilization

• Hard parts of organisms are more likely to Hard parts of organisms are more likely to be preserve than soft parts. be preserve than soft parts.

• Soft parts are likely to decay or be Soft parts are likely to decay or be consumed by other organismsconsumed by other organisms

• Because of this soft bodied creatures such Because of this soft bodied creatures such as jellyfish may not be fossilized eitheras jellyfish may not be fossilized either

• Buried organisms are more likely to be Buried organisms are more likely to be fossilized because it minimizes the decay, fossilized because it minimizes the decay, consumption, and destruction of the consumption, and destruction of the remainsremains

Types of FossilsTypes of Fossils

• Petrified FossilsPetrified Fossils – remains that become – remains that become buried in sediments and actually changed to buried in sediments and actually changed to rock.rock.

• MoldMold – a hollow space in sediment in the – a hollow space in sediment in the shape of an organism or part of an organismshape of an organism or part of an organism

• CastCast – copy of the shape of the organism – copy of the shape of the organism that made the moldthat made the mold

• Preserved RemainsPreserved Remains – entire organisms kept – entire organisms kept intact in ice, tar, or amber intact in ice, tar, or amber

• TracesTraces – other evidence that an organism – other evidence that an organism existed, ex. tracks, trails, footprintsexisted, ex. tracks, trails, footprints

Preserved Remains

Petrified Fossils

Impression - Cast and Mold

http://gpc.edu/~pgore/myphotos/fossils/cast&mold.jpg

http://www.fp.sfasu.edu/geology/GeologyTutorial/Fossils/CARBONization01.JPG

http://www.fossilmall.com/Stonerelic/amber/a25/bazaar_hemipteran_a25.htm

Trace fossil

http://www.dinosaursrock.com/SteveDiloposaurusFootPrint.jpg

Petrified wood

http://www.clas.ufl.edu/users/pciesiel/gly3603c/wood1.jpg

Age on EarthAge on Earth

• Scientists can determine a fossils age Scientists can determine a fossils age in two ways:in two ways:

• relative dating: used to determine relative dating: used to determine which of two rocks is older (layers at which of two rocks is older (layers at the top of the rock are younger than the top of the rock are younger than layers at the bottom)layers at the bottom)

• Absolute dating : used to determine Absolute dating : used to determine the actual age of fossilsthe actual age of fossils

Fossil RecordFossil Record

• The millions of fossils that scientists The millions of fossils that scientists have collectedhave collected

• A species is A species is extinctextinct if no members of if no members of that species are still alivethat species are still alive

http://www.carleton.ca/~tpatters/teaching/climatechange/rocks/rocks11.gif

Relative Dating Using Fossils

Geologic Time ScaleGeologic Time Scale

• A calendar of Earth’s history that spans A calendar of Earth’s history that spans over 4.6 billion years.over 4.6 billion years.

• Scientists have divided this large time Scientists have divided this large time period into smaller units called eras and period into smaller units called eras and periods.periods.

• The largest span in the calendar is the The largest span in the calendar is the Precambrian Era.Precambrian Era.

• Very few fossils are found from the Very few fossils are found from the Precambrian EraPrecambrian Era

Plummer et al 2003

Also called Hadean

http://books.nap.edu/html/creationism/evidence.html

Theories of EvolutionTheories of Evolution

• Gradualism – evolution occurs slowly Gradualism – evolution occurs slowly but steadilybut steadily

• Punctuated equilibria – species Punctuated equilibria – species evolve during short periods of rapid evolve during short periods of rapid changechange