Fossils, Strata and Dating What is it, where did it come from, how old is it?

I. Law of Uniformity = Processes that we observe working on the Earth today are the same as those that were working in the past. same process same speed ------------------------------------------------------------------------------------- Plates move Rock erodes Sediment deposits & forms sedimentary rock volcanoes create igneous rock

Relative Dating video https://www.youtube.com/watch?v=fYSeM63Fv0s

II. Relative Dating uses Strata (layers) A. Principles: 1. original horizontality – sedimentary layers start out horizontal (bcs sediment deposits bit by bit on ocean/lake bottom) 2. superposition – oldest sedimentary layers on bottom 3. crosscutting – things that cut horizontal layers are newer than the layers

Horizontality, Superposition, Crosscutting

III. Absolute Dating A. Based on half life 1. how long it takes for half of the atoms to decay https://www.youtube.com/watch?v=n8Cru41w5uI B. Each isotope decays at a different speed C. The amount of remaining tells us how long something has been around

To estimate the age of a rock find percent of U-235 remaining read graph

If no U-235 remaining try a different isotope

IV. Fossils A. Preserved remains organisms B. Form in sedimentary rock C. most no longer have organic material (no C-14) D. age of fossils that lack Carbon determined by 1. relative dating of sediment layers 2. radiometric dating of volcanic ash/rock nearby https://www.youtube.com/watch?v=XRW-ATOUJus start at 2:00

V. Types of Fossils A. cast = buried body decays and is replaced by sediment B. mold = imprint of body C. mineralization = minerals seep into a buried bone/tooth gradually replace organic materials D. unaltered = still bone..trapped in tar pit or ice or amber

Types of fossils Web site https://www.fossilguy.com/what-is-a-fossil/index.htm

bracketing http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/t ime/froshlec9.html