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.
What else could have caused K/Pg extinction?
Flood basalts in Deccan Trapps of india.
Acid rain
Ozone depletion
Greenhouse gas effects.
Basically it was a complex combination of factors (partially related to breakup of Pangea). Many species were already dying, but dinosaurs were OK until the impact. The environment was already stressed but impact was nail in the coffin. But not all the dinosaurs died, some avian dinosaurs survived and are our “birds” today!
What are meteors, bolides, meteorites, asteroids, comets?
meteoroids: small <1m rocks including
- meteors: as they enter atmosphere
-bolides: explode in atmosphere (firey)
-meteorite: if it survives entry to atmosphere.
Asteroids: large >1m meteorids
comets: rock mixed with ice: leftover from planet formation, has a tail of gas and dust.
Where do asteroids come from?
Series of belts between mars and jupiter.
Where do comets come from?
Kuiper belt (flat)and oort cloud (spherical).
What are the rates of meteor influx?
BIgger impacts happen less often. every year we get about 1 meter object size entering earth’s atmosphere.
Why does the moon have more craters?
Earth is harder to explore everywhere, its blocked by the moon, its atmoshphere protects it, and its overturned by plate tectonics more often. Craters eroded over time in bombardment phases.
What were the moons craters initialy believed to be? What was evidence of this?
Extinct volcanos! but there was a shoemaker' s hypothesis that geological changes arose from asteroid strikes. Common over geological time. Large circular structures with ejecta, shocked quartz and iridum. Came from evidence in Germany, a circular suevite rock broken up. more evidence in manicougan crater in quebec, oldest know crater. Same time as 2 other impacts 1. saint martin crater manitoba 2. rochecouart crater in france and 3. manicougan crater in quebec.
Did the 3 asteroids that hit earth at the same time come from the same source?
THey all line up along 22.8 latitude and it is impact due to fragmented comet/asteroid.
if it didn’t fragment it would have been much worse.
What is periodicity of mass extinctions? What is possibly causing this?
The biodiversity of the world decreases every 26M years. Raup and Sepkoski have a hypothesis about kicking comets from the oort cloud. Due to gravitational “kicks”
- Nemesis, a red dwarf companion star thats cooler than our sun, circling and when its closest its gravity pulls comets in.
- Planet X past neptune causing gravitational pull
- Moving through galactic plane, we were in danger zone 1 million years ago, but travel time is ALSO 1 million years so we may be in danger BUT. Statistics are rarely reliable. Over periodicities say 50m years so we’re good for now. Probably every 1/million years.
What is a historical smallish impact we talked about in class?
- Tunguska Russia, 50 m object, blowdown the eize of vancouver+surrey. Iron rich asteroid that exploded at 8km up, leaving no crater. Largest historical impact that had a huge release of TNT and 1000x hiroshima energy. leveled forest and caused shock wave that travelled 2x around the earth.
No crater only blowdown area. 3100km3 blowdown area.
What are some recent “near misses” that we talked about in class?
- May 1996 270m asteroid missed earth by 450000km and would have been the size of arizona if it landed. 2x eruption of mt. st. helens.
- July 2019 Asteroid 2019 OK passed earth within 73000km, 1/5 distance between earth and moon. almost hit satelites. discovered w one day of warning.
- Chelyabinsk meteor(bolide) Feb 2013 burned up in air, 10x strength of hiroshima, light brighter than the sun, burned in air 30 km above ground.
- Dec 2018 meteorite exploded over bearing sea, 10x strength of atomic bomb, very fast.
COMET SHOEMAKER-LEVY 9: massive impacts in solar system, in july 1992 it broke up due to jupiter’s tidal forces (when celestial bodies get too close to objects they’re orbiting) Saw impact on jupiter, 1m megatons of TNT, 2km fragments, if it hit earth it would have WIPED US OUT to microbial levels. Jupiter is our cosmic “vacuum cleaner”
Moon and jupiter are our impact shields,
What is the scale we talk about when discussing impacts?
Torino scale: comunicates potential threats on scale 1-10, assesses risk of near earth objects. (no, normal, attention, threatening, certain collision)
Uses spaceguard suvery: surveys all NEOs bigger than 1km. smaller ones not tracked. Track the ones with mass extinciton potential.
Future asteroid protection using NEOcam and infared + visible light.
How can we mitigate impacts?
Using TIME.
- Fragmentation: blow it up by drilling into it. Difficult to predict and multiple impact risk.
- Sudden orbit adjustment: explode nuclear warehead and smash projectiles into asteroid.
- Steady state orbit adjustment: chemical/electric or nuclear propulsion to drive it away from asteroid.
- Ablation systems: irradiate surface with laser or focus sunlight onto it with mirrors, would need orbiting satellinte around the impactor.
- Install solar sails (mirrors) or with reflective material (requires LONG warning period)
but in reality there are useless without warning. We need lots of $$$ to pull them off, shoemaker levy gave everyone a ‘wake up call’
Whats the risk of an impact?
1:20,000 similar to airplane crash. Tehre are other more pressing issues we need to look at instead.
