The Rock Record California Standards: IE.1a, d, g, h, I, k.

Did you know? California 10 to 12,000 years ago had mastodons, saber tooth cats, giant sloth's and horses? In two hours you can travel to southern California and see fossils of these and other animals?

La Brea Tar Pits in Southern California Woolly Mammoth

Andrewsarchus

Determining the Age of Rocks Uniformitarianism is the principle that the geologic process that are happening today happened 100 years ago as well as 10,000 years ago. So the geologic processes have been uniform throughout the ages.

Determining the Ages of Rock When scientists determine the ages of rock they can determine the relative age or the absolute age. The relative age of rock is based upon the principle that one layer below another must be older. Conversely, if a layer is above another it must be younger. This is called the relative age of rocks.

Law of Superposition When sedimentary rocks are deposited by erosion they form what is known as a bed or strata. The boundary between two beds is called a bedding plane. The Law of Superposition states that one bed or layer of rock below another is older than the one above.

Law of Superposition

Absolute Ages of Rock Geologists need to determine absolute age of rocks as well as the relative age of rocks. To say one layer is older than another based upon the law of superposition says nothing as to how old the rock really is.

Absolute Ages of Rock The absolute age of a rock can be determined by using radiometric dating. Radiometric dating is based upon the decay of radioactive minerals.

Structure of the Atom

Radioactive Isotopes Radioactive carbon, potassium and argon are used to determine the absolute ages of rocks. These radioactive elements when they are unstable, or change over time, are called isotopes.

These isotopes decay at a certain, predicable rate. The original element is called the parent isotope and the new element is called the daughter isotope.

Radioactive Decay of C-14 to N-14

Radio Carbon Dating How does carbon get into the Ecosystem here on Earth? Through photosynthesis carbon dioxide and water, with energy by the sun, is taken in by plants to produce oxygen, carbohydrates and energy. Animals such cows, dinosaurs, etc. eat the plants and when they die radioactive decay rate is started.

Radiometric Dating Geo- = rock/Earth Chronology – the study of time Chronometer is another name for a wristwatch or a clock. Geochronology is the study of time as related to Earth.

What is a fossil? 1. Record of prehistoric of life 2. Remains, imprints or traces of once living life 3. Preserved in rock Trilobite fossil

The Fossil Record A scientist who studies fossils is called a paleontologist. Paleo = ancient; -ology = the study of.

What do fossils tell us? Fossils not only tell us when and where an organism lived but also, how an organism lived.

What are the conditions for a fossil to be formed? 1. The animal or plant has to be protected from scavengers or microorganism. 2. Organism must be buried quickly by sediments. 3. Organism must have hard parts such as bones, shells, teeth, etc. 4. Fossils are usually found in sedimentary rocks.

Fossils are mostly found in sedimentary rocks.

Types of Fossils 1. Petrified remains 2. Carbonaceous Films 3. Molds and Casts 4. Original Remains 5. Trace Fossils

Petrified Remains 1. Petrified remains: are formed when the calcium from bones are replaced by quarts which is harder than calcium and therefore, is more resistant to weathering.

Petrified Forest, Arizona

Petrified Forest, Arizona

Carbonaceous Films 2. Carbonaceous Films: When a thin film of residue is left over from an organism forming an outline of that organism resulting in a outline of that organism. Coal is one type of carbonaceous film which serves as a source of fuel today.

Molds and Casts 3. Molds and Casts: When an impression is made in mud and compaction and cementation turn sediments into rock. The shell or bone decays leaving behind a cavity in a rock.

Original Remains/Trace Fossils 4. Original Remains: When a organism is trapped in resin or ice or tar and the remains are still intact. 5. Trace Fossils: Are fossils that show evidence of animal activity such as tracks, worm holes and burrows of rodents. Coprolites are fossilized scat.

Coprolite or fossilized scat.

Trace Fossils: Dinosaur tracks

Wooly Mammoths of California

La Brea Tar Pits, Southern California

Saber Tooth Cat

Index Fossils INDEX FOSSILS. Some fossils inhabited Earth for a very long time. Others remained unchanged for very short periods of time. When an organism existed on Earth for short periods of time, and were abundant and were widespread geographically theses were called… INDEX FOSSILS.

Index Species Scientists use Index Species to determine the age or rock layers. Only a few fossils are used to date the age of rock layers. Trilobite is an Index Species.

Index Fossils

Ammonite Fossil as Index Fossil

Burgess Shale located in NW Canada

Burgess Shale

Burgess Shale

The End