When Did we start thinking the EARTH is OLD? Darwin argued that earth could be billions of years old Small geological formations estimated to bee 300 million years old, based on observations of erosion. Kelvin estimated 20 million years based on cooling of the Earth. Scientists were debating between millions and billions, not billions and thousands!

Radiometric dating indicates that the earth is 4.6 billion years old

Fossils allow us to learn about extinct species Morphology Behavior Development

Most organisms don’t fossilize

Occasionally soft tissues fossilize Burgess shale 505 million years ago ~65,000 specimens ~93 species

Burgess Shale Discovered in 1909 by Charles Walcott Yoho National Park, British Columbia Made famous by Stephen J. Gould’s 1989 book: Wonderful Life Records fossil life after the Cambrian explosion

CAMBRIAN EXPLOSION 542 million years ago time at which most animal phyla first appear in the fossil record appears sudden in the fossil record

Burgess Shale: Gould Burgess shale life forms include things similar to contemporary animals and things not at all found in contemporary life Non-extant forms appear just as well adapted to Cambrian life as those forms that survived A new Burgess shale formation was found in 2013: 50 additional species

Fossils provide clues about behavior

Fossils provide clues about development

Scanning electron microscopy provides evidence of cellular structure Structure of melanosomes suggests striking plumage

DINOSAUR Courtship? Crest connected to nasal cavity Sound generated by blowing air Ears tuned to this frequency Younger animals had higher sound Older animals had deeper further ranging sound https://www.youtube.com/watch?v=xTXEhSBOecU