HON 301. Surviving the Anthropocene I. Welcome. Prof. F.M. Walter 28 August 2018

Transcription

1 HON 301 Surviving the Anthropocene I. Welcome Prof. F.M. Walter 28 August 2018

2 Movie: hdp://vimeo.com/

3 Earth 1 au from the Sun Equilibrium temperature: 247 K (-26C) Actual mean temperature: 287 K Albedo: 0.37 Radius: 6.4 x 10 3 km Mass: 6.0 x kg Differentiated into Inner core Outer core Mantle Crust

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5 Ages of the Earth Earth is 4.5 Gyr old Earth has changed over Mme DifferenMaMon Core cools Plate Tectonics Atmospheric evolumon And the Sun has changed too

6 Gross Equilibrium Earth is in equilibrium Changes in propermes over 4.5 Gyr have been minimal Liquid water has existed for >4 Gyr (273K < T < 373K)

7 Energy Balance (1- a) πr 2 (L / 4π d2) 4πR 2σT 4

8 The Gaia Hypothesis Earth is a complex self- regulamng system Life is an integral part of the planet, and affects the planet Feedback mechanisms alter planetary condimons: planetary condimons remain suitable for life. Hypothesis adributable to James Lovelock and Lynn Margulis (1970s) cf. Lovelock & Epton 1975 New ScienMst, (2/6/75) A metaphor, not a mechanism (S.J. Gould)

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10 The Hadean Earth. I Gyr Impacts melt the surface. VolaMles escape to space Source of atmosphere, oceans: outgassing and impacts Early atmosphere: CO 2, H 2 O, N 2, H 2 S, SO 2, H 2 Oceans exist by 4.4 Gyr Impacts: 4.5 Gyr Late Heavy Bombardment at 3.9 Gyr Lunar crater counts give this damng

11 The Hadean Earth. II. Details: Large impacts (200+ km) occurred ~ every 100 million years. These will melt the surface and strip the atmosphere. Atmospheres (H 2 O + CO 2 ) regenerated As surface cools, rain replenished oceans Life appeared with 100 Myr of end of great bombardment Then things got complicated

12 Geological Timespans: Eons Hadean Ends ~4 Gya with indirect evidence for life (kerogens) Archean Ends ~2.5 Gya with first O 2 catastrophe Proterozoic Ends ~0.54 Gya with first animal fossils Hadean, Archean, Proterozoic eons comprise the PreCambrian Phanerozoic now

13 Geological Timespans: Eras Phanerozoic Paleozoic Ends with formamon of Pangea ~ 250Mya Mesozoic Era of the dinosaurs Ends with the KT event ~66 Mya Periods: Triassic, Jurassic, Cretaceous Cenozoic

14 Geological Timespans: Periods Cenozoic Era Paleogene ends with ice 23Mya Neogene ends 2.58 Mya Quaternary

15 Geological Timespans: Epochs Quaternary period Pleistocene Ends 11,000 years ago ExMncMon of many large mammals Holocene Begins with Older/Younger Dryas climate changes

16 EvoluMon of the Atmosphere

17 Drivers of Atmospheric ComposiMon Exospheric escape Plate Tectonics Life

18 Atmosphere and Temperature Greenhouse gasses: CO 2 CH 4 H 2 O chloro- fluorocarbons Majority species today: N 2 O 2

19 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 O 2 Snowball Earth II may have spurred the evolution of animals (see

20 Evolution Driven by environmental stresses O 2 is toxic Led to Eukaryotes? Snowball Earth II Led to Metazoa?

21 Snowball - Evolution

22 Snowball - Oxygen

23 ConMnental Plates

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26 Plates in MoMon

27 Life and its Feedbacks There have been 5 major exmncmon events These are adributed to Asteroid impacts Climate change Biocide They usually occur over millenia A sixth exmncmon is in progress

28 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.

29 Precambrian ExMncMons Poorly documented fossil record End- Archean due to increased O 2 levels (biocide) First well- documented Precambrian exmncmon 650 Mya. Snowball Earth due to biogenic O 2? End- Vendian mass exmncmon 523 Mya Both led to diversificamon of life

30 Major Phanerozoic Extinction Events

31 Plus at least 19 lesser extinction events

32 Causes of Mass Extinctions

33 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

34 Other Possible Causes Nearby supernovae Ocean anoxia Glaciation/climate change Biocide Changes in atmospheric composition Effects of Oxygenation Human excesses

35 Atmospheric CO 2 levels Mya

36 From: Ex2nc2on, by D.M. Raup, 1991 (Norton)

37 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

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39 The Anthropocene Epoch That epoch when human beings affect the Earth s ecosystems Start: With the invenmon of agriculture 8000 BCE Industrial RevoluMon 1850 CE Nuclear capabilimes CE CO 2 accumulamon 1950 CE PlasMc accumulamon 1970s Synonymous with the Holocene?

40 Effects of Agriculture Alters ecosystems and the atmosphere Agriculture reflects more sunlight than forests (changes albedo) produces more CO2 than forests Reduces bio- diversity

41 Industrial RevoluMon Humans start modifying atmosphere by increasing CO 2 emissions Increasing parmculate emissions

42 Nuclear CapabiliMes Long- lived radioacmve nucleomdes yield detectable alteramons of chemical composimon of surface and atmosphere.

43 CO 2 AccumulaMons AccumulaMons increase circa 1950: Increased industrializamon Oceanic saturamon

44 PlasMc AccumulaMons

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46 Where will we go from here? Weeks 2 The Solar- Terrestrial relamon Weeks 3-4 Stability of the Earth and its atmosphere Weeks 5-6 Carrying capacity and Earth s human populamon Weeks 7-14 Futurology and other speculamve thinking