Mountaintop Fossil? The Esposito family was hiking on a mountain and found a shell fossil. They had different ideas about how it got there. Decide with whom you agree and explain: Mom: A bird picked up the organism and dropped it on the mountain top. Dad: Water, ice, or wind carried the fossil to the mountain top. Rosa: The mountain formed in an area that was once covered by ocean. Bill: The fossil flowed out of a volcano that rose up from the ocean floor.

The Rock and Fossil Record History of the Earth Uniformitarianism: Hutton (1795) Earth changes in the same way over long periods Past is key to future

What would the discovery of marine fossils on the top of Canadian mountains mean?

Catastrophism Believed earth only few thousands of years Changes happened quickly by catastrophes

What other types of catastrophes may happen on Earth?

Modern Geology Compromise neither uniformitarianism nor catastrophism accounts for all geologic change most geologic change is gradual and uniform, catastrophes have occurred

Relative dating The bottom layers of rock are usually the oldest layers. The top layers are usually the youngest layers. Scientists can use the order of these rock layers to determine the relative age of objects within the layers. Estimating the age of rock layers in this way is called relative dating. For example, fossils in the bot- tom layers are usually older than fossils in the top layers

Geologic Column Made by piecing together undisturbed rock columns from around the world (p.131)

Absolute Dating Measures the age of fossils or rocks in years by examining atoms. When an atom decays, it becomes a different and more stable kind of atom. Each kind of unstable atom decays at its own rate. the time that it takes for half of the unstable atoms in a sample to decay is the half-life By measuring the ratio of unstable atoms to stable atoms, scientists can determine the approximate age of a sample of rock. uranium-238 has a half-life of 4.5 billion years. scientists can use the decay of uranium-238 to date rocks or fossils that are millions of years old carbon-14 has a half-life of only 5,780 years. Scientists use carbon-14 to date fossils and other objects that are less than 50,000 years old

Naturally preserved evidence of life Most found in sedimentary rock! Fossils Naturally preserved evidence of life Most found in sedimentary rock! ----- Meeting Notes (9/30/13 11:17) ----- Number 18 on the study guide!!!

Fossils in Rock

Dinosaur Head

Bird Fossil in Rock

Tooth

Amber Fossils Hardened tree sap.

Frozen Fossils Wooly Mammoths Prehistoric man Asphalt Fossils: Trapped in sticky pools of tar Saber toothed tigers, snails, plants, etc. LaBrea Tar Pit, CA

Marine Fossils: Help scientists reconstruct ancient coastlines and shows the deepening and shallowing of ancient seas. Ex. Finding a marine fossil on top of a mountain

Trace Fossils Preserved evidence of animal’s activity Foot prints preserved in rock.

Molds and Casts Mold: cavity left when organism has decayed Cast: filled in mold and becomes rock Show changes in past environments and organisms

Index Fossils Found throughout world Lived for very short, well-defined period of time. Trilobites: found in rock layers 400 million years old

Geologic Time Scale Represents 4.5 billion years divided into distinct intervals Divisions: Eons ( largest divisions) Eras (contains 2 or more periods) Periods (longer than epoch, but shorter than era) Epochs (longer than an age, but shorter than a period)

Paleozoic Era Old life 540-248 mya From no land organisms to amphibians, plants, & insects Ended by largest mass extinction of Earth’s history Ocean changes – 90% died

Mesozoic Era “Middle Life” 248-65 mya Age of Reptiles (dinosaurs) Small birds & mammals toward end Global climate change ended

Cenozoic Era Recent life 65 million yrs ago to now Age of Mammals Some extinct: mammoths, saber-toothed, giant sloths