17 terms

Earth Sci: Chapter 32 - Earth history

Science that examines the ways in which earth sediments are deposited in demarcated layers known as strata.
The presence of characteristics found in two geographically separated rock layers which is interpreted as a common relationship between the layers. For example if two rock layers have the same kind of index fossil or unique chemical composition, the layers may have a common genesis in space or time.
index fossil
A fossil of an organism known to have lived in relatively short geologic age that can be used to date the rock layer in which it is found.
A geographic area with a coherent stack of sediments formed or forming in it. This is the "bowl" for layers of sedimentary rock.
law of original horizontality
Strata are originally deposited in level flat layers.
law of superposition
What's on top came last, what's on the bottom came first (for undisturbed layers).
lateral continuity
A rock layer may extend in all directions, making it possible to trace strata over vast areas.
law of cross-cutting relationships
A geologic strata which cuts through another layer is the younger of the two features.
relative dating
Dating technique that establishes a time frame in relation to other strata or materials, rather than absolute dates. EX: stratigraphy or index fossils
absolute dating
Determining the age of an object based on a chemical or physical property of item. EX: radiometric dating, varves, or annular rings
A boundary separating two or more rock types of markedly different ages, often marking a gap in the geologic record caused by erosion or other geologic event.
Geologic Time
A timeline that organizes the events in Earth's history based on significant events marked in the geologic record.
Eon, Era, Period, Epoch in descending order.
cambrian explosion
A sudden appearance in the geologic record of a great increase in the number and diversity of hard bodied multicellular life on Earth.
About 535 million years ago (535 Mya).
Geologic eons
Hadean (4+ Bya)
Archeozoic (2.5-4 Bya) single cell, soft bodied, little atmospheric O₂
Proterozoic (Cambrian - 2.5 Bya) Eukaryotes, atmospheric O₂ increasing
Phanerozoic (Cambrian - current) high atmospheric O₂, multicellular life
Phanerozoic eras
Paleozoic (535 -250 Mya)
KT Boundary - mass extinction 95% species
Mesozoic (250 - 65 Mya)
Cenozoic (65Mya - current)
Major Phanerozoic Extinctions (Boundaries)
PT - ends the Permian, 250 Mya, , 96% marine, 83% insect species
TrJ - ends the Triassic, 200 Mya, just before Pangaea breakup, 75% species
KPg - ends the Cretaceous, 65 Mya, Iridium/asteroid, 95% species
(formerly called KT)
Supercontinent Cycle
the episodic amalgamation and breakup of supercontinents which coincides with some major extinctions