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Interpreting Geological Change Section 4.1 p. 411-414 Section 4.2 p. 415-418 Section 4.3 p. 419-424 Learning Outcomes • Describe the nature of different kinds of fossils, and identify hypotheses about their formation • Explain and apply methods used to interpret fossils • Identify uncertainties in interpreting individual items of fossil evidence; and explain the role of accumulated evidence in developing accepted scientific ideas, theories and explanations What is a Fossil • Fossils are preserved impressions in rock that tell us when, where, and how living organisms lived and behaved millions of years ago • The word fossil means ‘dug out of the ground’. • The majority of fossils are found in exposed sedimentary rock. • The most common types of fossil rocks are limestone, sandstone and shale. • Paleontologists are scientists who study early life forms by interpreting plant and animal fossils • Most fossils are fragments or parts of skeletons, shells or other animal traces. • The inferences made suggest that life on Earth has changed a great deal over the past million of years Trilobite • Fossils found in younger rocks are much like the organisms living today. • Older rocks contain fossils of organisms that are extinct (no longer existing) 300 million years ago Formation of a Fossil • 4 Step Process • When the organism dies it remains on the ground • Sediment gradually covers it • Eventually the seiment with the organism inside it hardened into rock • When you crack open the rock, you will find the impression of the organisms skeleton • Remains of dead plants and animals that have been protected from scavengers can become fossilized in a number of ways: • petrified (rock-like) fossils preserve the bones of dead animals by using silica • an outline or impression from the carbon residue on rock surfaces can provide a carbonaceous film • original remains may be preserved in tar, amber or peat bogs • trace fossils are evidence of animal activity, like worm holes, footprints, and burrows Telling Time Geologically • The layers of sediment have formed over millions of years are called Strata • From studying the kind of rock and grain size in a layer of strata, geologists can gather information about the environment in which it formed • If found in limestone this layer of rock was originally at the bottom of the ocean • If the layer of strata is very think, the environment was stable for quite some time • A new layer is formed when something major changes in the environment • Rise in seawater would create a change in the type of sediments (would now be replaced by sediments found in deeper water • Where a fossil is found in a strata tells a paleontologist when that creature existed • Strata forms geological columns that let scientists know the approximate age of the fossilized organism • Youngest organisms closer to the surface • Oldest organisms closer deeper towards the bottom • This is what allows scientists to see the evolution of creatures over time Studying Sedimentary Layers • In areas where the layers of sedimentary rock are deeply eroded, geologists can study the fossil record over a large portion of Earths History • Grand Canyon • Red Deer River (Central Alberta) • The Royal Tyrrell Museum • • • • Opened in 1985, Named after Joseph Burr Tyrrell, Located in the Bad Lands of Alberta (Drumheller) 1884 while studying coal deposits, discovered 70 million year old dinosaur skull (Albertosaurus) • Sparked interest (turned out to be one of the worlds richest deposits of Dinosaur bones) • Museum now displays over 200 dinosaur remains Geological Time • Geologists have used the knowledge found from fossils to organize Earths history into geological time intervals • These time periods are called Era’s • An Era is based on a sequence of rock strata (oldest on bottom, newest up top) • Often named after areas where rocks from that period were exposed • Jurassic is named after Jura, a mountain range in France • Four Main Divisions of these sequences • Precambrian Era (4600 to 600 Million Year ago) • Formation of Earth • Fist simple organisms (bacteria) • First soft-body animals (no vertebrae) • Paleozoic Era (600 to 225 million years ago) • • • • • First Reptiles First large land animals (amphibians-Frogs) First Insects First Large land plants First fish with Jaws • Mesozoic Era (225-65 Million Years Ago) • Dinosaurs rule and become extinct • First flowering plants • First birds and animals • Cenozoic Era (65 million years ago to today • • • • Appearance of most modern day species Many more species of mammals First grasses First human like species (about 2-3 million years ago) Understanding Fossil Evidence • Fossils are very rare • It can be very hard to come up with enough concrete evidence to make general statements about how life occurred back then • Some fossils of Archaeopteryx have been discovered with feather like impressions, but too few to have been found to make a statement saying that all similar creatures at the time had feathers • Putting together a fossil is like putting together a puzzle with no picture, and potentially missing pieces • Very difficult • Requires knowledge of anatomy, and Imagination