HON 301 Surviving the Anthropocene I. Welcome Profs. E. Mendieta & F. Walter 2 February 2015 Movie: hIp://vimeo.com/39048998 Ages of the Earth •  Earth is 4.5 Gyr old •  Earth has changed over Ome –  DifferenOaOon –  Core cools –  Plate Tectonics –  Atmospheric evoluOon •  And the Sun has changed too Gross Equilibrium •  Earth is in equilibrium •  Changes in properOes over 4.5 Gyr have been minimal •  Liquid water has existed for >4 Gyr (273K < T⊕ < 373K) Energy Balance
(1-­‐a) πR⊕2 (L¤ / 4π d2) ⇒ ⇓ 4πR⊕2σT⊕4 The Gaia Hypothesis •  Earth is a complex self-­‐regulaOng system •  Life is an integral part of the planet, and affects the planet •  Feedback mechanisms alter planetary condiOons: planetary condiOons remain suitable for life. •  Hypothesis aIributable to James Lovelock and Lynn Margulis (1970s) cf. Lovelock & Epton 1975 New ScienOst, 65, 304 (2/6/75) A metaphor, not a mechanism (S.J.Gould) The Hadean Earth. I. 4.5 -­‐ 3.9 Gyr Impacts melt the surface. VolaOles escape to space Source of atmosphere, oceans: outgassing and impacts Early atmosphere: CO2, H2O, N2, H2S, SO2, H2 Oceans exist by 4.4 Gyr Impacts: • 4.5 Gyr • Late Heavy Bombardment at 3.9 Gyr Lunar crater counts give this daOng The Hadean Earth. II. Details: • Large impacts (200+ km) occurred ~ every 100 million years. • These will melt the surface and strip the atmosphere. • Atmospheres (H2O + CO2) regenerated • As surface cools, rain replenished oceans Life appeared with 100 Myr of end of great bombardment Then things got complicated Geological Timespans: Eons •  Hadean –  Ends ~4 Gya with indirect evidence for life (kerogens) •  Archean –  Ends ~2.5 Gya with first O2 catastrophe •  Proterozoic –  Ends ~0.54 Gya with first animal fossils Hadean, Archean, Proterozoic eons comprise the PreCambrian •  Phanerozoic –  now Geological Timespans: Eras Phanerozoic –  Paleozoic •  Ends with formaOon of Pangea ~ 250Mya –  Mesozoic •  Era of the dinosaurs •  Ends with the KT event ~66 Mya •  Periods: Triassic, Jurassic, Cretaceous –  Cenozoic Geological Timespans: Periods Cenozoic Era •  Paleogene –  ends with ice ages @ 23Mya •  Neogene –  ends 2.58 Mya •  Quaternary Geological Timespans: Epochs Quaternary period •  Pleistocene –  Ends 11,000 years ago –  ExOncOon of many large mammals •  Holocene –  Begins with Older/Younger Dryas climate changes EvoluOon of the Atmosphere Drivers of Atmospheric ComposiOon •  Plate Tectonics •  Life Snowball Earth
There have been at least 2 “Snowball Earth”
episodes
Both times:
weathering ceased,
volcanic activity restored the greenhouse, and
melted the oceans.
Snowball Earth I coincides with the growth of
atmospheric O2
Snowball Earth II may have spurred the evolution of
animals
(see www.snowballearth.org)
Evolution
Driven by environmental stresses •  O2 is toxic –  Led to Eukaryotes? •  Snowball Earth II –  Led to Metazoa? Snowball - Evolution
Snowball - Oxygen
ConOnental Plates Plates in MoOon Life and its Feedbacks •  There have been 5 major exOncOon events •  These are aIributed to –  Asteroid impacts –  Climate change –  Biocide •  They usually occur over millenia •  A sixth exOncOon is in progress Extinction
Two kinds:
- slow change into a new species
- sudden death
Most species that have ever existed on Earth are
now extinct.
The average species lasts about 1 million years.
Extinction is final.
Precambrian ExOncOons Poorly documented fossil record •  End-­‐Archean due to increased O2 levels (biocide) •  First well-­‐documented Precambrian exOncOon 650 Mya. –  Snowball Earth due to biogenic O2? •  End-­‐Vendian mass exOncOon 523 Mya Both led to diversificaOon of life Major Phanerozoic Extinction
Events
Plus at least 19 lesser extinction events
http://evolution.berkeley.edu
Causes of Mass Extinctions
Causes of Mass Extinctions
•  Flood Basalts
–  11 occurrences, all associated with extinctions
–  End Permian: Deccan Traps
•  Sea Level Drops
–  12 occurrences, coincide with 7 extinctions
–  Coincide with all 5 mass extinctions
•  Asteroid impact
–  KT extinction only
Other Possible Causes
•
•
•
•
Nearby supernovae
Ocean anoxia
Glaciation/climate change
Biocide
–  Changes in atmospheric composition
–  Effects of Oxygenation
–  Human excesses
Atmospheric CO2 levels
Mya
Gambler’s Ruin
Or - why you can’t beat the bank.
Start with a stake.
•  Assume even odds
•  Eventually you will lose your stake
Consider a genus with N species
If in a time τ there is an equal probability
of speciation or extinction, then
eventually all species and the genus go
extinct
The Anthropocene Epoch That epoch when human beings affect the Earth’s ecosystems •  Start: –
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With the invenOon of agriculture – 8000 BCE Industrial RevoluOon – 1850 CE Nuclear capabiliOes -­‐ 1945 CE CO2 accumulaOon – 1950 CE PlasOc accumulaOon – 1970s Synonymous with the Holocene? Effects of Agriculture •  Alters ecosystems and the atmosphere •  Agriculture –  reflects more sunlight than forests (changes albedo) –  produces more CO2 than forests –  Reduces bio-­‐diversity Industrial RevoluOon Humans start modifying atmosphere by •  increasing CO2 emissions •  Increasing parOculate emissions Nuclear CapabiliOes •  Long-­‐lived radioacOve nucleoOdes yield detectable alteraOons of chemical composiOon of surface and atmosphere. CO2 AccumulaOons AccumulaOons increase circa 1950: •  Increased industrializaOon •  Oceanic saturaOon PlasOc AccumulaOons Where will we go from here? •  Weeks 2-­‐3 –  The physical and philosophical nature of Ome •  Weeks 4-­‐5 –  Stability of the Earth and its atmosphere •  Weeks 6-­‐7 –  Carrying capacity and Earth’s human populaOon •  Weeks 8-­‐14 –  Futurology and other speculaOve thinking