Life on earth through time

Let’s start at the beginning...

• How did the solar system (and earth) form from a rotating cloud of dust, particles and gases?

4.6 By

Half-a-billion years later...• Lava plains and

moon craters date back to ~3.9 By

• How did the moon form?

Life, maybe• Marine sediment by

3.8 By; evidence for liquid water on earth

• Oldest fossil in 3.5 By old rocks in Western Australia

• Debate continues… is this really evidence for life at 3.5 By?

3500 Ma

Cyanobacteria

• Suggested to be an early form of cyanobacteria

• Stromatolites- layers formed by webs of filimentous cyanobacteria

Prokaryotes to Eukaryotes

• About a billion years of evolution gave us membrane-bound organelles

• Endosymbiotic theory

2100 Ma

O2 rich atmosphere• Photoautotrophs:

– 6 CO2 + 6 H2O-> C6H12O6 +6 O2

• Oxygenated atmosphere by 1.8 Ba• Aerobic organisms- use O2 to

covert food to energy is favorable relative to fermentation

Complex multi-cellular life• See a surge in

diversity of multi-cellular life ~600 My…

• Improvement in fossil record

• First chordates

600 Ma

Phanerozoic

• Apparent life

• Rich fossil record starts in middle age of the earth

Early fish

• Appear in upper Cambrian (550 Ma)• Jawless, cartilagenous and eventually the

bony fishes• Importance of the bony lineage

440 Ma

Land plants• A progression from

marine algae to freshwater algae to green algae

• Vascular land plants- have the ability to transport water and nutrients within plant

430 Ma

Trees• What are the

benefits of a woody trunk?

• With plants and trees well established, what is next?

370 Ma

Amphibians• Land dwellers• Return to water to lay eggs and for larvae to mature• Adaptations: 3-chambered heart, limbs and girdle

bones, sturdy but flexible spinal column, ear structure

360 Ma

Insects• First insects were

wingless• Wings appear in

late Carboniferous• Extensive

radiation before the Permian

300 Ma

Reptiles• Reproduce

without returning to water– Enclosed eggs– Pass through

larval stage– Born in essentially

adult form

290 Ma

Dinosaurs• Dinosaurs: started off small with

light build (225 Ma)• Large carnivores Jurassic and

Cretaceous• Were they cold or warm-blooded?

– Vascular development of bones– Relation to birds

210 Ma

Early Mammals

• Tiny shrew-like creatures• Reliable temperature control• Co-existing with Dinosaurs through

Mesozoic

210 Ma

Birds• Poor fossil record• Archaeopteryx: the

perfect evolutionary link between theropods and modern birds– Feathers on a reptile– Jaw bone with teeth– Wings retained claws

150 Ma

IMPACT!

65 Ma

K-T boundary• Bolide ~10 km in diameter crashed

into Earth sending up dust, ejecta into the atmosphere

• Cloud blocked sunlight and led to the demise of plants, base of food chain

• Marine and terrestrial animals perished

Whales• From land to sea• Descendents of

carnivorous land mammals, the earliest of whom could walk and swim

• With increasing size, lost limbs

• Adapted feeding strategy

50 Ma

Primates• Grasping, mobile

hand• Overlapping field

of vision• By 34 Ma-

anthropoids (apes, monkeys, humans)

34 Ma

Genus Homo• 2.4 Ma: Homo

habilis• 1.8 Ma: Homo

erectus• Increased cranial

capacity; sloped forehead, jutting jaw, robust teeth

2.4 Ma

Homo sapiens neaderthalensis• Heavy brow ridges,

chinless jaws, large brain cavity, short limbs, bulky torso

• Hunted, used fire for warmth, light, cooking, constructed shelters from the skins

• 34,000 yrs-replaced by Homo sapiens sapiens

320 ky

K-T boundary

Permo-Triassic boundary

Mass Extinctions

“Mother of all extinctions”• Late Permian: 90% of all marine species

lost or reduced; tropical marine invertebrates hardest hit

• On land, spore bearing ferns gave way to conifers, ginkoes and gymnosperms

• Amphibians, reptiles lost• Causes: Configuration of the continents,

loss of epeiric seas, ice on poles, volcanic activity

• Late Ordivician (440 My) and late Devonian ME’s triggered by global cooling with the growth of the ice caps- due to compressed biomes, lowered sea level

• Impacted: marine invertebrates• Late Devonian: again cooling- reefs

communities hit hardest

The influence of tectonics on climate

• Position of continents dictates:– Ocean circulation and heat transport– Sea level (freeboard)- Pangaea– Ability to form ice caps

Example: Miocene grasslands and horse evolution

• Closure of Tethys (~35 Ma) with collision of Africa and Eurasia

• Cooling & drying with loss of forests, expansion of grasses

Horse adaptations• Horses in Eocene (50

Ma): small, 4 toed, fed on shrubs and foliage

• Grasses expanded• Horses in Miocene

– Higher crowned teeth– Fewer toes– Bigger, stronger, faster

Organisms effect on the environment?

• Examples: – Photosynthesis– Spread of land plants– Nutrient cycling

The marine N cycle• Nitrogen is an essential nutrient the limiting nutrient• When there is more available

nitrogen in a useful form, primary productivity is higher, CO2 removed from atmosphere

“The biological pump”

Sedimentary 15N• Use stable

isotopes of N to identify relative inputs/outputs in ocean in past

• Sediment and microfossil samples

Peru-Chile Margin

Goals• Changes in productivity through

time• Variability in denitrification (the

removal of nitrate) in the Eastern Tropical North Pacific

• Understanding the role of the N-cycle in glacial-interglacial CO2 cycles