EOSCimpacts.docx

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Department
Earth and Ocean Sciences
Course
EOSC 114
Professor
Stuart Sutherland
Semester
Fall

Description
12/14/2012 • Biosphere:  regions of the surface and atmosphere of the earth or other planet occupied by living organisms  composed of ecosystems: hydrosphere, atmosphere, lithosphere  composed of individual species that have evolved through time • Best fossil species for biostratigraphy? 1. SHORT range = higher RESOLUTION 2. Common 3. Lived in environments where fossilization is likely to occur 4. Present in many different environments • BIOSTRATIGRAPHY: subdividing time and correlating using fossils • Cambrian Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous Paleogene Quaternary • Precambrian is 87% of Earth’s history • The base of new geological time periods/groups of periods defined on the RADIATION of new species • WHAT IS A MASS EXTINCTION EVENT? 1. At least 30% of species lost 2. Broad range of ecosystems 3. Short/Sudden • How many mass extinctions? (at least 5 in the Phanerozoic)  Cretaceous/Paleogene (K/P)  Late Triassic!  Permo/Triassic (Largest Extinction Event: permits evolution of dinosaurs)  Late Devonian!  Late Ordovician • What Causes Mass Extinctions? 1. Biologically-Based: competition, Predation, Pathogens 2. Physical Earth-Based! A) Changes in continental configuration I. Changes in climate/ocean cyclicity/sea level Example: Late Ordovician Extinction- Gondwana moves south II. The greater the land mass the lower the biodiversity Example: Permo-Triassic Extinction B) Atmospheric- Volcanism Greenhouse / cold house effects 3. Extraterrestrial-Based 4. Combination of many factors! Just a bad day for the biosphere Worst day for biosphere-Permo/Triassic 251 million years ago 95-98% of ALL species Less than 1 million years duration • Causes of the Permo-Triassic extinction? 1. Continental configuration- drop in diversity 2. Sea level fall- less ocean ridge activity 3. Oceanic stagnation- anoxia (absence of oxygen) 4. Possible extra terrestrial impacts 5. Climate Change 3 Siberian Traps - massive volcanic activity: 2-3 million km basaltic lava 2 CO released causes Greenhouse warming Raises global temp by 5°C Warms oceans- melts gas (methane) clathrates* [Methane (CH4) from decay of organic material. CH4 is trapped in water ice - common in deep ocean sediments] Methane is an even better greenhouse gas than CO 2 Further 5°C increase in global temperature- now 10° warmer Permo-Triassic extinction kills off many creatures- clears ecological space  A new reptile evolves during the Triassic and takes advantage of this..... The Dinosaurs K/P Extinction Event:  The Dinosaur Killer  At least 50% of ALL species lost  On Land: nothing over25kg survives (Note: Mesozoic Dinosaur time is bracketed by extinction events)  Not just terrestrial species  Marine fauna suffers  Ammonites/ marine reptiles  80- 90% Marine species lost Latest Cretaceous clay layer is enriched in iridium Iridium anomaly and clay layer is global Source of such high iridium? Comets/ meteorites... IMPACT SCENARIO Further Evidence: 1. Fern Spores vs Pollen Ferns: first to colonize fire impacted landscape Spores act as a “proxy” for forest fires Just after K/P have massive increase “spike” in the % of spores in sediments that are from ferns 2. Soot (dust & ashes) layers associated with the iridium layer evidence of massive global fires 3. Tektites: natural glass- produced by melting rocks during impact 4. Shocked Quartz: another impact feature cross-hatched lines= stress lines in the quartz crystal: Shock lamellae (thin layer/ membrane) 5. Tsunami deposits evidence of almost GLOBAL tsunami activity at end of Cretaceous The Crater: The Smoking Gun Drilling off coast of Mexico-Yucatan Peninsula“odd” rocks: Suevite: a breccia (fractured rock) showing evidence of melting Completely melted rocks Sits in core store for years until geophysics reveals a crater (180 km across) Chicxulub “Tail of the Devil" Impact Crater Tsunami deposits, shocked quartz, and tektites: thicker towards this structure Shallow entry: 20-30° Impact body 10 km across Most of ejecta towards NW 7 6.2 x 10 tonnes TNT 100km rock vaporized Initial Effects: vaporizes all close by / Forest Fires / Tsunami can now interpret the sediments found around the K/P boundary Longer term Effects: sun light shut off- nuclear winter (weeks-several months) photosynthesis stops on land AND in oceans after dust clears: water vapor remains in the atmosphere.. Greenhouse effect more Greenhouse gas: vaporization of Yucatan limestones: CaCO ->CO a3d ave2age global temperatures rises up to 10°C? rapid shift in environmental conditions: Cold House (months)- Hot House (years- decades) high energy blast: Nitrogen and Oxygen combines Oxides of Nitrogen Combines with water vapor to form nitric acid Acid rain acidifies oceans/ soils on land Yucatan Evaporites* (salts precipitated by evaporating bodies of water)  E
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