ASTR 380 Mass Extinctions.

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1 ASTR 380 Mass Extinctions

2 Midterm: Thursday October 9 In class, usual time - Closed-book, closed-notes, closed-everything! Will cover everything seen thus far in class - Emphasis on the slides presented in class - Reading from book (Chap. 3-6) to help you understand the slides Format will be different a bit from HW #1, #2: - No computation (no calculator, phone, etc) - Short answers (1-2 sentences à 1 paragraph) - Bring extra pens or pencils!

3 Reminder (from Lecture #5) Uniformitarism vs Catastrophism Uniformitarism: e.g. evolution Catastrophism: e.g. mass extinctions

4 Outline What is a mass extinction? Famous mass extinctions Outcome: the good and the bad

groups of related species, etc. http://upload.wikimedia.

5 Taxonomic Classifications To set the stage: life forms are divided up into categories Members of same species can produce viable offspring Genera (plural of genus) are groups of related species, etc.

Example: Animals Not all listed; most are worms! http://www.

6 Example: Animals Not all listed; most are worms!

7 Example: Human Taxonomy At a higher level: we are animals, chordates, and mammals. Many living relatives. Closest are chimps

8 The Point for Extinctions Individuals die constantly Species can be wiped out if they are outcompeted or their ecological niche is eliminated For genus to go extinct, all species in it must go extinct For family, all genera must go extinct e.g., >40,000 species in ground beetle family!

9 What is a Mass Extinction? We mean a sharp increase in the number of species/genus/family extinctions in a short time In last 540 million years (since we ve had complex life, Cambrian Explosion), we have had five in which >50% of animal species went extinct à The Big Five extinctions

10 What is a Mass Extinction? This plot is now a bit outdated but gives the main idea

11 What is a Mass Extinction?

12 What is a Mass Extinction?

13 Difficulties Establish extinction by noting that a species appears below, but not above, a rock layer But fossils are incomplete Can easily have gap because of this Makes duration of event tough to say For some organisms, instant extinction could look like millions of years in rock! But mass extinctions need not be catastrophic Also, there are few beds of rock that cover the whole period seamlessly

14 What Killed the Dinosaurs? More generally, this is the K-T extinction ~65 million years ago Dinos had dominated land for 160 Myr Mammals too quick? Don t be silly! Other explanations? Sidney Harris

15 Surge in Volcanic Eruptions? Deccan Traps Huge uprise in eruptions in India Peak about 66 Myr ago; before K-T Gases might have played some role

17 Iridium A key fact: at K-T geological boundaries, there is a layer that is enriched in iridium (rare heavy metal) by factors of hundreds Why???

18 Luis and Walter Alvarez Luis (father), physicist Nobel Prize, 1968 Walter (son), geologist Combo, and two others, noted that iridium is common in asteroids Might there have been a giant impact?

19 Known Impacts: Meteor Crater ~50,000 years ago. ~1 mile across; impactor ~50m

20 Known Impacts: Tunguska Siberia, June 30, 1908 Flattened 80 million trees over 830 sq miles Probably caused by small comet or asteroid (~50 m?) No fatalities, but 4 hrs earlier would have hit St. Petersberg

21 Known Impacts: SL9 Shoemaker-Levy 9 Comet, broken into fragments by Jupiter s gravity >20 hit Jupiter in 1994 Largest had energy of 6,000,000 megatons of TNT!

23 Chesapeake Bay Impact Crater Largest impact crater in the US! Suspected in 1983 from drilling core taken off Atlantic City, NJ, far off to the north Extent of crater revealed in 1993 via oil exploration

26 Rates, Human Fatalities vs. Size

27 How to Test Impact Hypothesis? Impact matched rates and iridium But many geologists insisted that the volcanic eruptions that produced the Deccan Traps were the extinction culprit How else could one test the impact hypothesis?

28 Candidate Crater: the Smoking Gun Chicxulub crater: Discovered in late 1970s; oil drilling > 180 km in diameter Dated to 65 Myrs ago Clear impact; tektites etc. Size of bolide > 10 km Convinced most people

29 Impact of an Impact K-T: 100 trillion (10 14 ) tons of TNT equivalent Global dust, block photosynthesis for years Nuclear winter? Global firestorms; increase CO 2, cause greenhouse effect Possible acid rain

The Permian-Triassic Extinction Most extensive ever 240 million years ago 96% of all marine species 83% of all genera 70% of terrestrial vertebrae 57% of all families 53% of all marine

30 The Permian-Triassic Extinction Most extensive ever 240 million years ago 96% of all marine species 83% of all genera 70% of terrestrial vertebrae 57% of all families 53% of all marine families only 18% for K-T Only known mass extinction of insects Most famous victim: trilobites What caused this? Less certain, but let s explore

31 Causes of Permian-Triassic Extinction? Not clear Impact? Maybe, but tougher to nail down that long ago Volcanic eruptions? Climate change? Claimed recent evidence that the extinction was <160,000 years long, maybe <10,000 yrs

33 Precambrian Extinction 650 Myr ago Before hard parts! 70% of dominant flora, fauna extinct Possible causes? Ah, there lies a tale that speaks to the vitality of life and the special nature of water...

Reminder from Lecture #7: Evidence of equatorial glaciers, 600-700 Myr (if it happened; disputed) Why?

34 Reminder from Lecture #7: Evidence of equatorial glaciers, Myr (if it happened; disputed) Why? Ice reflects light, so Earth grows cooler Maybe caused by arrangements of continents How would we escape? Snowball Earth

35 Escaping Snowball Earth If Snowball Earth happened, we obviously escaped. But how? Volcanic eruptions would eventually release enough CO 2 for greenhouse Radioactive decay energy trapped under ice would also be released Ice floats, otherwise would settle and presumably wipe out ocean life

36 Human-Induced Extinction Mainly habitat destruction, pollution At current rate, estimate half of all species extinct within the next 100 years; rate is increasing Would be faster than any on record

37 Could All Life be Extinguished? Super-giant impact? 100 km would have 1000x K-T energy But bacteria in rock, deep ocean would probably survive Might kill off humans

38 Death by Supernova / Gamma-Ray Burst? Exploding star, ~10 10 times brighter than Sun for months At 1 parsec, would double heat from Sun Some supernovae produce gamma-ray bursts Some bacteria would probably survive Don t worry, nearest prospect is hundreds of parsecs away (but it is not so in the inner Galaxy ) 470x458,0.jpg

39 Death by Supernova / Gamma-Ray Burst? Exploding star, ~10 10 times brighter than Sun for months At 1 parsec, would double heat from Sun Some supernovae produce gamma-ray bursts Some bacteria would probably survive Don t worry, nearest prospect is hundreds of parsecs away (but it is not so in the inner Galaxy )

40 Benefits of Mass Extinction Opens up many evolutionary niches Precambrian: animal explosion (Cambrian Explosion) Permian Triassic: dinosaurs and mammals K-T: big mammals and eventually us! A little rebellion, now and then, is a good thing --- Thomas Jefferson (in a letter to James Madison dated January 30, 1787)

41 Summary Many mass extinctions; five big ones in last ~540 million years Always some animals / plants survived, undoubtedly many bacteria / archea too Some would be serious enough to kill us off But benefit is allowing new species to emerge

42 Question Say a few words about the Chesapeake Bay Impact Crater

History of life on Earth Mass Extinctions.

History of life on Earth Mass Extinctions. Agenda or Summary Layout A summary of the topics discussed 1 2 3 4 Explanation of Mass extinctions The five major mass extinctions Two particular extinctions