The Rock Record Chapter 8

p.185 Uniform itarianism A principle that geologic processes that occurred in the past can be explained by current geologic processes. Volcanism and Erosion

p.186 Relative Age The age of an object in relation to the age of other objects

Law of Superposition Newest Oldest p.187 The law that a sedimentary rock layer is older than the layers above it and younger than the layers below it if the layers are not distrubed Newest Oldest

Un ities p.189 Click Here to see animation conform Un ities p.189 Click Here to see animation A break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time.

p.191 Absolute Age The numeric age of an object or event, often stated in years before the present. Using a process like “radiometric dating” or “carbon dating”

p.192 Rates of Deposition In general, about 30 cm of sedimentary rock are deposited over a period of 1,000 years. However, a flood can deposit many meters of sediment in just one day.

p.193 Radiometric Dating A method of determining the absolute age of an object by comparing the relative percentages of a radioactive (parent) and a stable (daughter) isotope. Half-Life: the time required for half of a sample of a radioactive isotope to break down.

Carbon-14 Dating p.1 Plants absorb Carbon during Photosynthesis Scientists compare the carbon isotopes 12C and 14C (radioactive) This can be used to determine the ages of wood, bones, shells and other organic remains that are less than 7,000 years old.

Paleontology The scientific study of fossils.

p.199 Trace Fossils Fossilized evidence of past movement of an animal such as tracks, footprints, borings and borrows.

p.200 Index Fossils A fossil that is used to establish the age of rock layers because it is: Distinct – features different from other fossils Abundant – occurs in fairly large numbers Widespread – present in scattered rocks Existed only for a short span of geologic time

Eras & Periods Precambrian makes up about 88% of Earth’s history! Paleozoic Mesozoic Cenozoic Precambrian makes up about 88% of Earth’s history! Most rocks from that time have been severely deformed and altered by plate tectonics. Fossils are rare because life-forms lacked bones, shells or other hard parts to make fossils. The most popular Precambrian fossils are Stromatolites.

Eras & Periods Fossils of the first vertebrates appear (Paleo…) Precambrian Paleozoic Mesozoic Cenozoic Fossils of the first vertebrates appear (Paleo…) Most fossil fuels (coal and oil deposits) formed during the Carboniferous Period. “Carbonization” is the term for how plant remains were turned into coal and oil.. The Super-Continent “Pangea” formed at the end of this era – about 250 million years ago!

Eras & Periods Mesozoic: known as the Age of Reptiles Precambrian Paleozoic Mesozoic Cenozoic Mesozoic: known as the Age of Reptiles Dinosaurs first appeared during the Triassic Period, but they really dominated in the Jurassic Period. Dinosaurs supposedly became extinct when a giant meteorite crashed into Earth (impact hypothesis).

Eras & Periods Cenozoic Era is known as the Age of Mammals. Precambrian Paleozoic Mesozoic Cenozoic Cenozoic Era is known as the Age of Mammals. Human civilization developed during the Quaternary Period.