Geological Time

What is catastrophism?

Earth shaped by great catastrophes

What is uniformitarianism?

Present is key to the past. Same processes shaped Earth

What is relative dating?

Places rocks and events in order without exact ages

What is absolute dating?

Gives actual numerical ages in years

What does the law of superposition state?

Oldest rocks at bottom. Youngest at top

What is original horizontality?

Sediments are deposited horizontally

What is cross-cutting relationships?

Younger feature cuts through older rock

What are inclusions?

Rock with inclusions is younger

What is an unconformity?

Break or gap in the rock record

What is angular unconformity?

Tilted rocks below. Flat rocks above

What is disconformity?

Parallel rock layers with a time gap

What is nonconformity?

Igneous.metamorphic below. Sedimentary above

What is correlation of rock layers?

Matching rocks of same age in different regions

What are fossils?

Evidence of past life

What is a petrified fossil?

Minerals fill cavities

What is replacement fossil?

Original material replaced by minerals

What is a mold fossil?

Organism dissolves leaving hollow shape

What is a cast fossil?

Mold filled with minerals

What is carbonization?

Thin carbon residue remains

What is an impression fossil?

Surface print in fine sediment

What is preservation in amber?

Organism trapped in tree resin

What is indirect fossil evidence?

Tracks. Burrows. Coprolites

What conditions favor fossil preservation?

Rapid burial. Hard parts

What is radioactivity?

Spontaneous decay of atomic nuclei

What is radioactive decay?

Unstable parent changes into stable daughter

What is a parent isotope?

Unstable original isotope

What is a daughter isotope?

Stable isotope formed after decay

What happens in alpha emission?

Lose 2 protons. 2 neutrons

Alpha emission effect?

Atomic number -2. Mass number -4

What happens in beta emission?

Electron emitted from nucleus

Beta emission effect?

Atomic number +1. Mass unchanged

What happens in electron capture?

Electron joins proton to make neutron

Electron capture effect?

Atomic number -1. Mass unchanged

What is half-life?

Time for half of nuclei to decay

What does radiometric dating require?

Closed system

What does radiometric dating provide?

Numerical dates

What is Carbon-14 half-life?

5730 years

What is Carbon-14 dating used for?

Dating recent events

Where is Carbon-14 produced?

Upper atmosphere

If parent:daughter ratio is 1:15 and half-life is 1 million years

age?

What does the geological time scale do?

Divides geologic history into units

How was geological time scale first created?

Using relative dating

What is an eon?

Greatest span of time

What are the four eons?

Phanerozoic. Proterozoic. Archean. Hadean

Most recent eon?

Phanerozoic

Oldest eon?

Hadean

What is an era?

Subdivision of an eon

What are Phanerozoic eras?

Cenozoic. Mesozoic. Paleozoic

What is Cenozoic?

Recent life

What is Mesozoic?

Middle life

What is Paleozoic?

Ancient life

What comes after era?

Period

What comes after period?

Epoch

Why is dating the time scale difficult?

Not all rocks are databl