Lab 8 Dating of Rocks, Fossils and Geologic Events PDF

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Lab 8 Dating of Rocks, Fossils and Geologic Events Two main ways of Dating Relative Dating, Steno’s Law Original horizontality Superposition Cross-cutting relationships Lateral Continuity Absolute dating

Steno’s Laws 1666: Nicholas Steno proposed several principles that are used by geologists to determine the age of fossils and rocks in a process called relative dating (a method of sequencing events in the order they happened) 1 Law of superposition The bottom layer of a rock formation is older than the layer on top 2 Law of Original Horizontality Rocks are laid down horizontally and may later become tilted, faulted, or folded 3 Law of Lateral Continuity Layers of sediment extend in all directions horizontally unless a river erodes them or an earthquake moves them 4 Law of Cross-cutting Relationships A vein of rock or a fault that cuts across a rock’s layers is younger (more recent) than the layers. The middle and top layers formed after the bottom layer but before the vein. 5 Law of Inclusions If a rock body contains fragments of another rock body, it must be younger than the fragments of rock it contains The intruding rock must have existed first to provide the fragments Unconformity Represents a large gap in time; 3 types

Floral and Faunal Succession Fossil plants (flora) and animals (fauna) record an increasing complexity of lifeforms form younger rocks to older ones Index fossils: distributed worldwide but for short span of geologic time

Absolute Dating Atoms of the parent isotope decay radioactively to daughter isotopes at exponential rate that does not change Rate of decay expressed in terms of half-life (time it takes for half the parents to decay to daughter atoms)

Excerise Oldest 1st: BCD

Youngest A

E

3rd: EPGLCHOMDJASNKBRF

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