The History of Life on Earth As We Know It

The History of Earth Earth is ~ 4.5 billion years old Earth’s history is divided into four eons –Hadean Eon: (Gk: Hades - the netherworld) –Archean Eon: (Gk: Arche - ancient) –Proterozoic Eon: (Gk: Protero - former) –Phanaerozoic Eon (Gk: Phanero - visible, apparent)

The History of Earth The most recent eon is divided into three eras –Paleozoic Era (Gk: Paleo - ancient) –Mesozoic Era (Gk: Meso - middle) –Cenozoic Era (Gk: Ceno - recent)

The History of Earth eras of the modern eon are divided into periods –Paleozoic Era Cambrian Period Ordovician Period Silurian Period Devonian Period Carboniferous Period Permian Period

The History of Earth eras of the modern eon are divided into periods –Mesozoic Era Triassic Period Jurassic Period Cretaceous Period –Cenozoic Era Tertiary Period Quaternary Period

Earth’s History: Changing Conditions Table 22.1

Earth’s History: Changing Conditions atmospheric oxygen concentration has risen from near 0 to ~21% See Figure 22.3

Earth’s History: Changing Conditions atmospheric oxygen concentration has risen from near 0 to ~21% mean temperature has fluctuated significantly sea level has fluctuated significantly continents have entirely changed positions relatively gradual changes rapid, climate-changing events “catastrophic” events have modified the evolution of life

Log-log Oxygen levels Figure 22.4

Changes in Earth’s Mean Temperature in the Modern Eon Figure 22.5

Changes in Sea Level in the Modern Eon Figure 22.2

Earth’s History: Changing Conditions atmospheric oxygen concentration has risen from near 0 to ~21% mean temperature has fluctuated significantly sea level has fluctuated significantly continents have entirely changed positions

mid- Cambrian Continental Drift (~510 mya) (forming Gondwana) Figure 22.9

Devonian Drift ( mya) Figure 22.11

Permian Drift (formation of Pangaea) [~ mya] Figure 22.13

Cretaceous Continental Positions (~100 mya) Figure 22.15

“catastrophic” events have modified the evolution of life Dramatic climate change –End of Ordovician, Devonian, Permian, Triassic, Cretaceous Volcanism –End of Permian –During Triassic, Cretaceous Meteorite collisions –End of Triassic, End of Cretaceous

Figure 22.6

“catastrophic” events have modified the evolution of life several mass extinctions have occurred –repeatedly, up to 75% of species became extinct –afterward, new life forms proliferated and became dominant - evolutionary radiation

Dating events in Earth’s history absolute dates are estimated from the decay of radioactive elements relative ages are determined by the position in a series of rock layers –remains of dead organisms are mineralized (fossilized) under the right conditions anaerobic undisturbed proper geochemistry

Dating events in Earth’s history absolute dates are estimated from the decay of radioactive elements half-lives of some radioactive isotopes 14 C - 5,700 years 40 K x 10 6 years 238 U x 10 9 years

Figure 22.1

Figure 22.8

Figure 22.7

changing faunas Figure 22.17

The History of Life on Earth Earth’s past biotas are represented by fossilized remains ~300,000 described species Earth’s different ages are characterized by different types of fossils boundaries defining the eras and periods of the modern eon represent changes in fossil assemblages

The History of Life on Earth Fossils from successive ages reveal patterns –particular fossil types are found in rocks of the same age –new types of organisms appear sequentially in younger rock layers –types of organisms in shallower (younger) layers more closely resemble extant organisms –the appearance of new types of organisms occurred at different rates through time

three dominant world faunas Figure 22.17

The History of Life on Earth Fossils from successive ages reveal patterns –three faunas dominated animal life over time –size and complexity of organisms increased with time –predators became more efficient; defenses became more effective –extinction happened a typical species exists for ~10,000,000 years ~99% of species are extinct

The History of Life on Earth Fossils from successive ages reveal patterns –few innovations novel structures are rare most diversity is variation on existing body plans

The History of Life on Earth Fossils from successive ages reveal patterns –microevolutionary change: change that modifies species

Sticklebacks - no predatory fish, short spines Figure 22.20

The History of Life on Earth Fossils from successive ages reveal patterns –macroevolutionary change: change that produces new types of organisms

The History of Life on Earth The history of Earth is characterized by dramatic changes –gradual structural and climatic changes punctuated by catastrophic events The history of life on Earth is characterized by increases in size, complexity, competition & predation

Geologic History from a Biologist’s Point of View