HISTORY OF LIFE – CHAPTER 12Freshman Honors Biology

FOSSILS

Studied by paleontologists Remains of past dead organisms Forms in sedimentary rock Include

Eggs Whole skeletons and pieces of them Footprints Even coprolite…(animal poop)!

EVIDENCE FROM FOSSIL RECORD

Change over Time Over 99% of species that have lived on

Earth are extinct Extinct- all members of the species are

dead Extinction

DATING FOSSILS

Relative Dating Age of fossil is determined by its location

compared to other fossils Find relative age by comparing

Rock layer location- laid down in order from bottom (oldest) to top (youngest)

Index fossil location- fossil of know age Must occur in a wide geographic area Be easily recognizable Only lived for a short period of time

DATING FOSSILS

Radioactive Dating (Absolute age) Age of fossil is determined by determining

a ratio of radioactive elements in the fossil Radioactive elements decay into other

elements Decay is predictable and consistent Half-life- the amount of time it takes for half of

a sample to decay

GEOLOGIC TIME SCALE

Divided into eras and then periods

MAJOR EVENTS IN EARTH’S HISTORY

Evolution of Macromolecules Unicellular organisms Eukaryotic cells Multicellular organisms

Endosymbiotic theory- eukaryotic cells created from symbiotic communities of prokaryotes Double membrane around many organelles Some organelles contain their own DNA and DNA

looks like prokaryote DNA