Impacts Flashcards
What is the age of the earth? (schools of thought through time)
James usher thought earth was creased 4004 BC.
Uniformitarianists thought the present was the key to the past, and measured the rate of crust formation and how long it would take to form, thought millions of years.
Kelvin calculated rate of cooling from molten earth body, thought 20-40 million years. All wrong. THe earth is 4.55 billion years old!
Oldest rock is 4.04 Ga in Acasta Gness in NWT.
Found meteorites 4.55 Ga, dated using radioactive half lives.
What are the divisions of the geological time scale? write them out!
do it with the slides nicola!
What is the biosphere?
Thin layer of life on earht’s surface composed of ecosystems.
i.e. arctic ecosystem, interconnected.
Used to look very different (ordovician or cretaceous)
What is stratigraphy and biostratgraphy?
Stratigraphy: studying layers of rock (strata)
Biostratigraphy: identified relative ages of rock layers using fossils.
Time is recorded in layers of rock, helps us look at evolution of species through time, helps with passage of time on earth.
Who is James hutton?
Uniformitarianst who says present is the key to the past. Same natural laws and processes that operate in universe have always operated this way and apply everywhere.
Who is Nicholas Steno?
Principles of stratigraphy!
- Law of superpositoin: whats on top is youngest
- Principle of original horizontality: if its tilted or folded it used to be flat.
- Principle of lateral continuity: if its here its over there too
- Principle of cross cutting relationships: if it cuts through, its younger”
ie. dikes!
What is siccar point?
Great example of an unconformity: period of non deposition or active erosion. Tilted sediments originally deposited in a desert from devonian period, and verticle rocks containing marine fossils deposied in silurian next to each other with an unconformity in between.
What was the concept of extinction and who thought of it?
George Cuvier: established elephants were different species in different places (indian vs african) and conclued that mammoths used to be alive but become extinct.
IMPORTANT: people used to think fossils were just dead things, never though that htey were once alive.
Who is william smith?
Principle of faunal succession. FOssils succeed each other vertically in a specific order identifiable over long distances. CORRELATE OVER CONTINENTS.
Strata of the same age can be dated and correlated using their FOSSILS.
Only works because of evolution. Fossils must change for this to work.
What is an INdex fossiL?
Ideal species in biostratigraphy. needs 4 things
- A short range, to make higher resolution of age. i.e. ammonites are commonly used (251-66ma)
- common
- wide geographical distribution
- died in environments for good fossilization/preservation.
can correlate time using these index fossils.
When were the 5 major extinction events?
End of Cretaceous 65ma End of Triassic 205 ma Permian-Triassic 251ma Late devonian 360ma Late ordovician. 450ma
What is radiation of a new species?
after an extinction event, rapid diversification occurs into more species, mass extinctions make new resources available and creates more challenges: more NICHEs.
First appearance of new fossils helps geologists define start of a new period.
What is background extinction?
ALways some species are becoming extinct, a constand background level of extinction. Many things have become extinct since last ice age, currently rate is about 100 extincitons per million species per year.
- caused by humans? likely.
What defines a mass extinction?
30% of species lost
Broad range of ecosystems
Short/sudden. 1ma maximum
What is the order of taxonomy?
Kindom, Phylum, class, order, family, genus, species.
What causes mass extinctions?
- Biological causes.
- competition, predation, pathogens, biogeology (mosses)
Often don’t cause MASS extinctions. - Physical (earth based)
a) - continental configuration, tectonics. changes in climate, ocean cycles, sea level. Ice ages.
Example: late ordovician extinction happened as gondwana moved towards south pole.
Fragmentation leads to biodiversity, on land and in oceans.
i.e. pangea is a dry arid environment
b) atmospheric/volcanism
- cold or greenhouse effect. Gases released. - Meteor imacts, bolide events. Linked to some mass extinctions.
Often a combination of factors.
Describe the Permian Triassic (end permian extinction)
251 Ma
The “Great dying”
98% of all species went extinct.
Killing of dimetrodons allowed room to make the dinosaurs. among other things.
Many creatures were gone and cleared the niche for new reptiles to evolve. (dinosaurs)
What caused the permo-triassic extinction?
- Continental configuration (Pangea: drop in diversity, less niches lead to less diversity and vast deserts present)
- Sea level fall related to less ocean ridge activity
- Ocean Stagnation - anoxia, polar waters don’t sink so no circulation.
- Possible impacts from ET objects.
- Climate change: siberian traps (volcanic activity) siberian outpouring of basaltic lava)
2-3 million km3 of basaltic lava. High c02 in the atmosphere.
- caused greenhouse gas effect and raised temps by 5 degrees. THIS ALSO released clathrates which add another 5 degree increase to make 10 degree increase.
What are clathrates?
Solid ice crystal structure containing trapped methane from decay of organic material, common in deep ocean sediments. When the ocean warms it melts these and releases the methane.
What is the end Triassic extinction? What caused it?
201 ma, happened again before biosphere could recover from the Permian Triassic. Field site in BC.
75% of all species extinct. Many large amphibians and plant species extinct. Conodonts die.
Causes?
1. Gradual climate chance (stress on biosphere)
2. Extraterrestrial impact (quebec) several craters but Rochecuart is too small and Manicougan (quebec) is too late
3. Volcanic eruptions: flood basalts of central atlantic magmatic province (CAMP)
What is the Crestaceous Paleogene extinction?
Dinosaur killer! 65ma
50% of species lost, no land animal above 25kg survives, ammonites and marine reptiles are lost (90% of marine species)
Abrupt change in the fossil record.
What is the Alvarez Hypothesis? What’s the evidence for it?
Mass extinction caused by large asteroid (luiz and walter alvarez found high levels of iridium at k/pg boundary. Iridum is rare on earth and mostly comes from ET objects (comets/meteors).
also found…
1. soot layers with iridium (forest fires)
2. Ferns spores (dominant after a forest fire)
3. Tektites (common ejecta of natural glass from melting rocks during impact
4. Shocked quartz (cross hatched lines indicate stress due to impact) found at boundary.
5. Tsunami deposits found around the globe.
6. Chicxulub impact crater at Yucatan peninsula in mexico. 180km across, thick layers of ^^evidence towards crater.
Largest known on earth. 10km diameter.
Seismic refraction using P and S wave speed shows changes in density of ocean bottom over large areas indicating sediments have filled in a very large crater.
complex crater with ring and central peak.
odd rocks were found in the crater suggesting melting
SUEVITE: breccia, fractured rock formed during impact events.
imact killed things. 30 degee entry angle, energy 6,2 tonnes x 10^7 tnt, 100km3 vapourized rock. 1500km air blast radius.
what are suevites?
rocks made of brecciated material. glass (partial melting/cooling) , rock. formed during impact event.
What would the effects be from the Crestacious paleogene impact?
Initially: vapourize everything nearby, forest fires, combusion, global tsunami.
Short term: global nuclear winter for a few months, things die cause no photosynthesis or light. When dust clears, water vapour remains in the air and greenhouse effect is enhanced, also yucatan limestones (when vapourized) would release c02 and increase greeenhouse gas effect.
Longer term: greenhouse effect for decades,
-global volcanic activity increased in biosphere (co2 outgassing, global temp, pressure on ecosystems),
-the burning of atmosphere made nitrogen oxides which combine with water vapour to create acid rain. Oceans and soils acidified.
-Salts precipitate form yucatan evaporites, rich in sulfates causing more acid rain.
