Fossils and the Rock Record Chapter 21 Fossils and the Rock Record

Geologic History Principles Law of Uniform Processes Law of Superposition Law of Cross-cutting Relationships Law of Included Fragments

Law of Uniform Processes The processes which are changing the earth’s surface today are the same processes which acted in the past

Law of Superposition The oldest rock layer is on the bottom of an undisturbed rock column, and each higher layer is younger

Law of Cross-cutting Relationships A fault or intrusion is younger than the rock layers it cuts through

Law of Included Fragments Pieces of one rock found in another rock must be older than the rock in which they are found

Tree Rings This tree was approximately how old? About 17 years How did you determine this age? By counting the number or light (summer) and dark (winter) rings

Geologic Time Scale Which represents the longest time interval – era, eon, or epoch? Which of the three eras represents the longest amount of time? Approximately how old is the earth? eon paleozoic 4.6 billion years

A B C D E F G X H I J K L Y Relative Age: List the following rock layer in chronological order starting with the oldest layer.

Relative Age In the previous slide you know rock layer Y is younger than rock layer C because _________________________________. In the previous slide you know rock layer H is older than rock layer I because _________________________________. In the previous slide you know rock layer X is younger than rock layers D, E, and F because _________________________________. Y cuts across C H is under I D, E, and F are included in X

____________ Age: By measuring the percentages of parent and daughter isotopes in some rocks or fossils, an age in years of that object can be determined. Absolute

Fossils Picture C shows what two types of fossils, and how do they form? Picture D shows what type of fossil? Picture B shows what type of fossil? Mold-organism decays Cast-mold fills with minerals Trace fossil Actual remains

Chapter 21 Review (clues on next slide) G a s t r o l i t h n d e x fo s i l f o s i l c o p r l i t e a m b e r v o l u t i n p e m n e r a i z a t i n c a s m o d

Ch 21 Review (continued)

Ch 21 Review (continued) ___1.Nonconformity – ___2. Angular Unconformity- ___3.Disconformity- B sedimentary over nonsedimentary C sedimentary over tilted sedimentary A sedimentary over horizontal sedimentary

Ch 21 Review (continued) paleozoic ancient life end marked by many extinctions, including dinosaurs mesozoic cenozoic recent life

Ch 21 Review (continued)

Ch 21 Review (continued)