Transcript Slide 1
Fossils: Our Keys to the Past and Evidence of Evolution By: Shannon Reardon Adam Bouchard and Kristan Brodie http://www.kpbsd.k12.ak.us/chapman/demers/images/collage2.JPG What is a fossil? • A fossil is remains of ancient life • Fossil is derived from the Latin term fossilis - meaning any object extracted from the ground including minerals and archeological artifacts paleo ology (the study • In the 18th century paleontology of ancient life) was created = old or ancient = study of Why are fossils important? • It enabled scientists to see occurrence of extinction in different species • It gave Darwin evidence that earth is older than previously believed and that very slow changes over a long period of time can add up to substantial changes in organisms • Can be used to correlate and match up rock units from different places giving relative ages • It shows evidence of continental drift – the theory that continents were once one large landmass Plummer et al 2003 Fossilization ization = TO MAKE • Hard parts of organisms are more likely to be preserved than soft parts. • Soft parts are likely to decay or be consumed by other organisms • Because of this soft bodied creatures such as jellyfish may not be fossilized either • Buried organisms are more likely to be fossilized because it minimizes the decay, consumption, and destruction of the remains BURIED IN SEDIMENT OR SOIL Types of Fossils • Unaltered remains – original material of the organism has not been changed to another substance • Altered remains – original material has undergone permineralization, recrystalization, replacement, carbonization • Impressions – organisms leave an imprint in sediment, can form casts and molds • Traces – other evidence that an organism existed, ex. tracks, trails, footprints Unaltered Parts http://www.studyworksonline.com/ cda/image/preview/0,1127,1309,00 .jpg Altered remains Carbonization of a leaf http://www.fp.sfasu.edu/geolog y/GeologyTutorial/Fossils/CARB ONization01.JPG Impression - Cast and Mold http://gpc.edu/~pgore/myphotos/fossils/cast &mold.jpg Permineralization – petrified wood http://www.clas.ufl.edu/users/pciesiel/gly3 603c/wood1.jpg Trace fossil http://www.dinosaursrock.com/Steve DiloposaurusFootPrint.jpg Radioactive Dating and Geologic Time Scale By Adam Bouchard Age on Earth • EVIDENCE suggests age of the Earth is about 4.6 to 4.7 billion years old • Evidence is gathered from radioactive dating of rocks from the earth, moon and meteorites • Relative age : places rock units or geologic events in sequential order • Absolute age : numerical or chronological age of a rock or geologic event Radioactive Dating Definitions • Radioactive isotope - an atomic form of a chemical element that is unstable • Radioactive decay - the spontaneous nuclear disintegration of certain isotopes • Radioactive dating – a way of determining the age of rocks and fossils on a scale of absolute time. It is based on the half-life of radioactive isotopes • Half-life – the time it takes for ½ the atoms of the radioactive parent to decay to atoms of the daughter element Newest layer Oldest layer