Lecture 5
The Origin and Evolutionary History
of Life on Earth III
The Origin and Evolutionary History of Life on
Earth
• Chemical conditions of the early Earth
• A model for the first cells
• First life
• Life changes the planet: oxygenating Earth’s
oceans and atmosphere
• Eukaryotic cells descended from prokaryotic
cells
• History of life on Earth
1
Paleozoic era (542-251 mya)
• Devonian period (416-359 mya)
– jawed fishes, amphibians, and insects
first appear
– jawed fishes diversify and dominate
the seas (Age of Fishes)
– vascular plants diversify and dominant
the land
2
Paleozoic era (542-251 mya)
• Devonian period ended in a mass extinction
event (2nd of the big five)
3
Paleozoic era (542-251 mya)
• Carboniferous period (359-299 mya)
– reptiles first appear
– amphibians diversify and are the dominant
terrestrial carnivores (Age of Amphibians)
– most of today’s major coal deposits are the
remains of organisms that lived in this period
4
Paleozoic era (542-251 mya)
• Permian period (299-251
mya) – by the end of this
period, the continents
have merged as the
Pangaea supercontinent
5
Paleozoic era (542-251 mya)
• Permian period (and Paleozoic era)
ended (251 mya) with a mass
extinction event (3rd of the big five)
– the largest mass extinction on record
(as much as 95% or more of all species)
– more than 90% of the marine species
and 70% of land vertebrates vanish
– apparently took place in a time span of
only a few hundred thousand years,
which is fast in the geological time
scale
6
Mesozoic era (251-65 mya)
7
Mesozoic era (251-65 mya)
• diversification and dominance by reptiles – the
whole era is often called the Age of Reptiles
(sometime called the Age of Dinosaurs, but many
non-dinosaur reptiles were also prominent)
8
Mesozoic era (251-65 mya)
• Triassic period (251-200 mya)
– dinosaurs and mammals first appear
– gynmnosperms are the dominant land plants
Coelophysis, one of the earliest
known dinosaurs
9
Mesozoic era (251-65 mya)
• Triassic period (251-200 mya)
– ended with a mass extinction event that paved
the way for the dinosaurs to rise to prominence
(4th of the big five)
10
Mesozoic era (251-65 mya)
• Jurassic period (200-146 mya)
– dinosaurs dominate the land (and
other large reptiles dominate the seas
and the skies)
– birds evolve from a dinosaur lineage
Stegosaurus
Archaeopteryx
Mesozoic era (251-65 mya)
• Cretaceous period (146-65
mya)
– flowering plants
evolved around the
early Cretaceous and
diversified quickly
– many animals
(especially insects)
appear to have
coevolved with
flowering plants
(different species
affecting each other’s
evolution)
12
Mesozoic era (251-65 mya)
• the era ended (65 mya) with a mass extinction
event (5th of the big five)
– dinosaurs essentially all died out (unless you count
birds as dinosaurs, which some scientists do)
– most gymnosperms also died out, as did many marine
organisms
13
Mesozoic era (251-65 mya)
– evidence points to the impact of a large
extraterrestrial body as a likely cause of the
extinction event
14
Mesozoic era (251-65 mya)
• a major impact almost certainly occurred at this time;
iridium layers worldwide and deposits from tsunamis
around the Gulf of Mexico coast of the time provide
clear evidence of this
15
Mesozoic era (251-65 mya)
• a large crater site in the
Yucatán Peninsula of Mexico
is likely the result of this
impact
16
Mesozoic era (251-65 mya)
• the extent to which such an impact could affect the
biosphere is still debated, but is accepted by more and
more scientists as at least a contributing factor to this
massive extinction event
Cenozoic era (65 mya – present)
• usually called the Age of
Mammals, but:
– birds,
– insects,
– and flowering plants
have also undergone massive
diversification and have all
achieved some measure of
“dominance” in the biosphere
during this era
18
Cenozoic era (65 mya – present)
• two periods, Paleogene (65-
23 mya) and the Neogene (23
mya – present)
– an older division into Tertiary
(65-~2 mya) and Quaternary
(~2 mya – present) is still often
referred to
19
Cenozoic era (65 mya – present)
• the Neogene has been
marked by:
– many ice ages
– the rise of humans
– and mass extinctions
– most of these mass extinctions
may have been caused by the
ice age climate, humans, or both
– the current mass extinction
event (we are in one now, the
sixth extinction ) is mostly
caused by humans
20
