Chapter : Geographic Setting and Impacts to the Environment
Geological time with major evolutionary events in the
fossil record
William L. Kruczynski and Pamela J. Fletcher
65
Cenozoic
Paleozoic
MYA Era
0
1.8
Period Major events
Quaternary:
Tertiary:
Human evolution
Mammals diversify
Cretaceous:
Proterozoic:
145
Mesozoic
Life begins in sea
Extinction of dinosaurs,
First primates,
First flowering plants
Jurassic:
First birds,
Dinosaurs diversify
199
Triassic:
First mammals, First dinosaurs
Permian:
Carboniferous:
Archean:
Oldest rocks,
Earth curst forms
4000
First reptiles,
Trees, seed ferns
359
416
Hadean:
Earth forms
Devonian:
First amphibians,
Fish diversity
Silurian: First vascular plants
444
Ordovician:
Major diversification of animal life
488
4600
542
Cambrian:
First fish,
First chordates (animal with backbone)
Adapted from Encyclopedia Britanica and www.enchantedlearning.com
Major extinction, Reptiles diversify
299
Paleozoic
2500
PRECAMBRIAN
251
7KHgeological time scale is a method of relating the timing and relationship between events that have occurred
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in the geologic record. Geologists and earth scientists have used the relationship between layers and types of rocks,
presence of plant and animal fossils, and radioactive dating to assemble a sequence of historical events that have
occurred over geologic time.
Geologic time is divided into four large segments called Eons: Hadean, Archean, 3URWHUR]RLFDQG3KDQHUR]RLF
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Periods, a unit of geologic time in which a single type of rock system is formed. Some Periods are divided into
Epochs that are not shown on this chart, but a discussion of Epochs appears on subsequent pages in this chapter
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appearance and disappearance of shorelines and coral reefs.
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
Geographic Setting and Impacts to the Environment
542
PHANEROZOIC
MYA Eon
0
Cenozoic
65
Mesozoic
251