SSO 102. Welcome to the Anthropocene I. Introduc7ons. Prof. F.M. Walter 23 January 2018

Transcription

1 SSO 102 Welcome to the Anthropocene I. Introduc7ons Prof. F.M. Walter 23 January 2018

2 Movie: hep://vimeo.com/

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5 Ages of the Earth Earth is 4.5 Gyr old Earth has changed over 7me Differen7a7on Core cools Plate Tectonics Atmospheric evolu7on And the Sun has changed too

6 Gross Equilibrium Earth is in equilibrium Changes in proper7es 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- regula7ng system Life is an integral part of the planet, and affects the planet Feedback mechanisms alter planetary condi7ons: planetary condi7ons remain suitable for life. Hypothesis aeributable to James Lovelock and Lynn Margulis (1970s) cf. Lovelock & Epton 1975 New Scien7st, 65, 304 (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. Vola7les 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 da7ng

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 forma7on 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 Ex7nc7on of many large mammals Holocene Begins with Older/Younger Dryas climate changes Anthropocene

16 Evolu7on of the Atmosphere

17 Drivers of Atmospheric Composi7on 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 Con7nental Plates

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26 Plates in Mo7on

27 Life and its Feedbacks There have been 5 major ex7nc7on events These are aeributed to Asteroid impacts Climate change Biocide They usually occur over millenia A sixth ex7nc7on 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 Ex7nc7ons Poorly documented fossil record End- Archean due to increased O 2 levels (biocide) First well- documented Precambrian ex7nc7on 650 Mya. Snowball Earth due to biogenic O 2? End- Vendian mass ex7nc7on 523 Mya Both led to diversifica7on 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 Contributor of full cause?

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 terrestrial ecosystems Start: With the inven7on of agriculture 8000 BCE Industrial Revolu7on 1850 CE Nuclear capabili7es CE CO 2 accumula7on 1950 CE Plas7c accumula7on 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 Revolu7on Humans start modifying atmosphere by increasing CO 2 emissions Increasing par7culate emissions

42 Nuclear Capabili7es Long- lived radioac7ve nucleo7des yield detectable altera7ons of chemical composi7on of surface and atmosphere.

43 CO 2 Accumula7ons Accumula7ons increase circa 1950: Increased industrializa7on Oceanic satura7on

44 Plas7c Accumula7ons

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46 Where will we go from here? Week 2 The Solar- Terrestrial rela7on Weeks 3-4 Climate change and its effects Weeks 5 Carrying capacity and Earth s human popula7on Weeks 7-9 Futurology and other specula7ve thinking Automa7on and work; future of transporta7on Privacy and interconnectedness War and the fates of civiliza7ons Week 10 Solu7ons and their ramifica7ons