CHAPTER 19 Earth’s Evolution through Geologic Time
478
A rc he an E on (P re c a m b ri a n )
P r o t e r o z o ic E o n (P re ca m br ia n )
P a le o z o ic E ra
P a le o z o ic E ra
C e n o z o ic E r a
M e s o z o ic E r a
Quaternary
Period
Tertiary
Period
Cretaceous
Period
Jurassic
Period
Triassic
Period
Permian
Period
Pennsylvanian
Period
Mississippian
Period
Devonian
Period
Silurian
Period
Ordovician
Period
Cambrian
Period
4,600 Ma
First multicelled
organisms
1,000 Ma
Formation
of Earth-Moon
system
Present
2,500 Ma
542 Ma
Outgassing
produces
primitive
atmosphere
3,800 Ma
Oldest known fossils–
stromatolite-forming
cyanobacteria
Cambrian
explosion
First
jawless
fish
First
insects
Fishes flourish
First
amphibians
Gymnosperms
flourish
First reptiles
First dinosaurs
First birds
Conifers
abundant
First flowering
plants
65.5 Ma
Dominance of
amphibians
First horses
Mammals, birds, insects
and flowering plants flourish
Grasslands
widespread
Invertebrates
dominate the sea
First vascular
plants invade
the land
Extensive
coal swamps
251 Ma
Great Permian
extinction
First mammals
Dinosaurs
dominate
First primates
Extinction of dinosaurs
and many other species
First whales
First
apes
Extinction of
many giant
mammals
Evolution of
genus Homo
Oxygen accumulates
in atmosphere
2,200 Ma
48 8 M a
4 4 4 M a
4 1 6 M a
359 Ma
3 1 8 M a
2 9 9 M a
1 4 5 .5 M a
1 9 9 .6 M a
2 .6 M a
Ma = million years ago
FIGURE 19.21 The evolution of life through geologic time.