PTYS 214 Fall Announcements. Materials from last week moved to web page. Midterm #4 next Tuesday!

Transcription

1 PTYS 214 Fall 2017 Announcements Materials from last week moved to web page Midterm #4 next Tuesday! 1

2 Previously Radiometric Dating Compare parent / daughter to determine # of half lives 14C, 40K, 238U, 232Th, 87Ru Evidence for Early Life Fossils Biomarkers Isotopes O2 Life started early! 2

3 Previously Atmospheric O Respiration Ozone good / bad O sources / sinks Evidence for early O history BIFs Detrital uraninite and pyrite Redbeds Sulfur MIF Forest fires O / life history > 2.5 Ga (Archean): >.5 Ga (Proterozoic): present (Phanerozoic): 1 ppm single-celled few % primitive multi-celled % macroscopic life Mass extinctions 3

4 Mass Extinctions All genera Well- defined genera Trend line Big Five mass extinctions Other mass extinctions >15% of animal families died or > 40% of animal genera died The Big Five : 1) Cretaceous/Paleogene (K/Pg or K/T): ~65 Myr ago 2) Triassic-Jurassic: ~205 Myr ago 3) Permian-Triassic: ~251 Myr ago 4) Devonian-Carboniferous: ~365 Myr ago 5) Ordovician-Silurian: ~445 Myr ago 4

5 Taxonomy Species: Homo Sapiens (all people) Genus: Homo (humans and close relatives) Family: Hominidae ( great apes : humans, chimpanzees, gorillas, orangutans) Order: Primates (all apes and monkeys) Class: Mammalia (mammary and sweat glands) Phylum(division): Chordates (vertebrates) Kingdom: Animalia (moving consumers) Domain: Eukarya (complex cells) 5

6 Mass Extinctions Sharp decrease in the number of species in a relatively short period of time Rapid event - 10,000 to 100,000 years A significant part of all life on Earth became extinct (use of families is more reliable than species; for example extinction of 18% of all families corresponds to about 40% of all genera and 70% of all species) Extinct life forms from various phyla, lived in different habitats, spread out over the whole world 6

7 Studying Extinctions The older the fossil record gets, the more difficult it is to read it (and the less samples that are available)! Use indirect evidence as well, like isotopic changes (for example, 13C) After a mass extinction fauna and flora are dominated by opportunistic species ('weeds', 'pests ) After a mass extinction species experience rapid reproduction, diversification 7

8 Cretaceous/Paleogene (K/Pg) Extinction (Formerly Cretaceous / Tertiary (K/T) 65 million years ago at least 75% of animal species (17% of all families) went extinct in a very short interval of geologic time PALEOGENE AFFECTED LAND AS WELL AS SEA LIFE Many types of fossil disappeared fossils found above the boundary are much smaller and less abundant than below K/P boundary 8

9 Geologic K/Pg Boundary First major stratigraphic boundary identified (early 1800) shows dramatic change in the types of fossils deposited on either side of this boundary Divides the "Age of Dinosaurs" from the "Age of Mammals Raton Basin, NM, USA 9

10 The Impact Theory No Dinosaur Tertiary Fossils Clay layer clay layer Dinosaur Cretaceous Fossils Iridium A team led by Walter Alvarez (a geologist) and his father Luis (a Nobel physicist) discovered that the clay layer contains an anomalous high concentration of iridium Alvarez et al (1980) Extraterrestrial cause for the Cretaceous-Tertiary extinction. Science 208,

11 The Iridium Anomaly Siderophile (iron-loving) element - dissolves in molten iron Abundant in meteorites Chondrite What about the Earth? Ir is depleted in the Earth s mantle and Earth s crust; why? Iridium is more abundant in meteorites, i.e., asteroids, than in Earth s surface rocks, so the Alvarez team proposed that a large asteroid impacted Earth at that time One small problem Where is the crater? 11

12 Over the years evidence accumulated Impact-indicators were found worldwide: - Iridium - Stishovite/coesite (Shocked Quartz) - Microtektites (molten spherules) 12

13 0.32 mm quartz grain Shocked Quartz Under intense pressure (but limited temperature), the crystalline structure of quartz is deformed along planes inside the crystal (planar deformation features) 13

14 Spherule layer (microtektites) K/Pg Spherules Archean Spherules Microscopic glassy particles formed from molten rock ejected from the impact craters Smit, J. (1999) Annual Review of Earth and Plan. Sci. 27, p

15 Impact Cratering Like in a large explosion, a lot of energy is used to break, melt, vaporize material Very fast (few seconds to a few minutes) Very high temperatures and pressures Crushing - Melting - Vaporization Trinity test + 3 sec. Comet (D=10 km) 10 km Ocean (4 km) Crust Trinity test + 10 sec.15

16 Impact Cratering Like in a large explosion, a lot of energy is used to break, melt, vaporize material Very fast (few seconds to a few minutes) Very high temperatures and pressures Crushing - Melting - Vaporization Trinity test + 3 sec. 10 km Trinity test + 10 sec.16

17 The Earth has many impact scars Barringer Crater 1200 m (0.75 miles) in diameter, Produced by a m object about 49,000 yr ago Manicouagan 100 km in diameter Produced by an asteroid about 5 km in diameter ~ 210 Myr ago 17

18 Very large impact craters can be seen on the Moon 18

19 Large impacts are rare! And Earth has plate tectonics! Chances to find the K/Pg crater are small 19

20 Florida The K/Pg crater The Chicxulub crater in the Yucatán peninsula, Mexico, is widely accepted as the K/Pg impact crater Age: ~65 million years BIG! 195 km Gulf of Mexico Cuba Central America BURIED (1 km of sediments) NASA-JPL Shuttle Radar Topography mission Schrodinger, Moon Galle, Mars Hildebrand et al. (1991) Geology 19,

21 Consequences of the K/Pg impact Tsunami Hours Waves created by an impact in the ocean Only affects coastal regions After initial devastation, back to normal Important Reminder: Over 70% of the Earth s surface is covered by deep oceans and seas Oceanic impacts are ~3 times more likely than land impacts K/Pg impactor occurred into a shallow sea Not a rare event, more like a typical occurrence 21

22 Global Consequences of the K/Pg impact Heat Pulse Hours-Days Re-entering ejecta heats up as it goes through the upper atmosphere (friction!) to 1,000K 1,500K Hot ejecta cools down by radiating IR (thermal) energy Surface receives a significant amount of radiation 22

23 Global Consequences of the K/Pg impact Heat Pulse & Wildfires Hours-Days Ground may have been similar to an oven set to broil for about 20 minutes! Affects land regions, killing above ground animals Not enough to trigger wildfires everywhere on Earth (probably not enough to kill all above ground animals)! Goldin and Melosh, Geology 37, p ,

24 Global Consequences of the K/Pg impact Climate Perturbation Few Years Cooling from injection of dust and formation of sulfate aerosols (sulfur released by evaporites) in stratosphere Darkness may last for months! Photosynthesis? Not long enough to trigger an ice age! 24

25 Global Consequences of the K/Pg impact Acid Rain Gases distributed all over the world Sulphur dioxide released into the atmosphere Few Years Acid rain due to rain-out of sulfate aerosols Damage to vegetation? Acidification of oceans? Gases dissolve in rainwater Acid rain kills plantlife, pollutes rivers and streams, and erode stonework 25

26 Global Consequences of the K/Pg impact Greenhouse Effect Decades or Longer Warming from injection of CO2 (released by shocking carbonates) in the atmosphere Mild Effect Temperature increase: droughts floods Melting of glaciers Not enough CO2 injection for a catastrophic effect! 26

27 K/Pg Mass Extinction Summary 65 million years ago at least 75% of animal species (about 17% of all families) went extinct in a very short interval of geologic time It affected land AND sea life Best working hypothesis: the extinction was triggered by the large impact event that created the Chicxulub structure It is not clear which consequence(s) associated with the impact was the main cause of the extinction possibly, it was a series of effects 27

28 Other Suggested Causes Climate Change (either warming or cooling) but how intense, and what caused it? Colossal Volcanic Eruptions but they went on before and after! Sea Level Changes causing extinction in oceans and continental interiors? Methane release from methane clathrate deposits how large and how abrupt is the climatic effect? There may have been a combination of causes! 28

29 What about other extinctions? All genera Well- defined genera Trend line Big Five mass exctintions Other mass extinctions K/Pg extinction No big iridium spikes or other impact indicators associated with other mass extinctions No major mass extinctions associated with other large craters on Earth Many hypotheses, but we don t quite know what triggered most mass extinction events! 29

30 Where did the K/Pg impactor come from? Asteroids: small bodies that are made of rock or iron - Located in the Asteroid Belt (between Mars and Jupiter) Comets: small bodies made of rock and ice ( dirty snowball ) - Located in the Oort Cloud and in the Kuiper Belt Outer SS Inner SS Jupiter 30

31 Homework Homework #16 available shortly on the web site 31