1. Don’t Waste Time! Chapter 6: The Rock and Fossil Record

2. Why Do We Care About Time? We are used to referring to time in terms of hours, days, weeks, months, and years. But, to geologists, dealing with events that occurred a couple million years ago is RECENT to them! Most geologic processes happen over very long periods of time before we can see any results. Examples are mountain building, tectonic plate movement, and island formation. So how long has the Earth been around? About 4.6 billion years (according to fossil evidence)

3. Dividing Up Earth’s History The divisions of Earth’s geologic history are created due to MAJOR events like a mass extinction, mountain building, or evolutionary changes in lifeforms Four major divisions: 1.Eon: Phanerozoic means “visible life”, which is the eon we are currently in! 2.Era: Paleozoic (“ancient life”), Mesozoic (“middle life”), and Cenozoic (“recent life”) 3.Period: each era is divided into periods which are used in rock and fossil dating 4.Epoch: only the periods of the Cenozoic era are divided into epochs because humans came into existence during this time!

5. Stratigraphy (the study of rock layers) When you look at a cross-section of rock layers, you can use relative age dating techniques to figure out when the layers were deposited 3 laws used in relative dating: 1.Law of Superposition: rock layers are youngest at the top of the sequence and older as you go down 2.Law of Horizontality: all layers of rocks are deposited horizontally to begin with and then tectonic forces tilt or bend them 3.Law of Intrusions: the igneous intrusion is always younger than the surrounding rocks

6. This Could Get Uncomfortable! Unconformities are created by erosion interrupting deposition What happens is that deposition stops, erosion removes previously formed rocks, and then deposition resumes 3 types: 1.Angular: tilted layers overlain by horizontal layers 2.Disconformity: horizontal layers interrupted by erosion 3.Nonconformity: sedimentary rocks deposited over igneous rocks

7. Disconformity

8. The Age of the Dinosaurs The Age of the Dinosaurs The most widely accepted theory of dinosaur extinction 65 million years ago is of a huge, 6- mile wide impact near the Yucatan Peninsula. The impact site is called the Chicxulub Crater, a Mayan term meaning “tail of the devil”. The impact was similar to a large explosion, along the lines of 100 million megatons of TNT. The impact ejected rock into the atmosphere from several kilometers beneath the surface of the Earth and carved out a bowl-shaped crater nearly 100 km in diameter. Additional material was lofted in an expanding, vapor-rich plume that included gas from the vaporized asteroid or comet. This plume rose far above the Earth's atmosphere, enveloping it, and eventually depositing a thin layer of debris around the entire world. In addition, the shock of the impact produced magnitude-10 earthquakes, which were greater than the magnitude of any we have ever measured in modern times.