Module 17 Flashcards
Over ___% of all species on the planet became extinct during the Cretaceous-Paleogene (K/P) extinction event
extinction more severe on land or ocean?
land few creatures over ___ survived
- exceptions? why?
- 50%
- ocean
- 25kg
exception crocodiles and alligators cuz generalist and survive a long time w/o eating?
who discovered that K/P had a meteorite impact?
what did they investigate?
Luis and Walter Alvarez
clay layer that occurs in a geological section that crosses the K/P boundary in Gubbio, Italy
what was going on with the clay at the K/P boundary
1cm clay on top Cre rock enriched with Ir, 300X normal
where does It usually exist?
what did the clay Ir possibly come from?
space stuff
meteor/comet over 10km in diameter, prob responsible Cre extinction
what does Fern spores/ pollen show?
ferns quick colonize after fires
take vertical core sed and see if spore spike -> lots forest fires
what else is associated w/ Ir Clay
soot
evidence massive global fires
what are Tektites
composed of natural glass and produced during impact events.
During impact, rock is melted/ejected from the crater, travels through the air and cools, it forms characteristic aerodynamic shapes
many found at K/P bound suggest massive impact
what is shocked Quartz
fractures produced when rock is shattered during a high-energy impact. The fragments are called shocked quartz
lots at K/P bound particularly b/w N and S America
Tsunami deposits
evidence mega tsunami at the K/P boundary in Mexico, Texas, New Jersey, and the Carolinas
not explainable tsunami generating phenomena operating on the Earth (earthquakes, volcanoes and landslides)
Chicxulub Impact Crater
Yucatan Peninsula of Mexico
had melted rock suggesting the area had been subjected to some form of extreme stress.
large circular disturbance over 180 km in diameter
- entry around 20 - 30° and is estimated to have been at least 10 km across (size mount Everest)
- impact was equivalent to 6.2 x 107 tons of TNT
- 100 km3 of rock to be vaporized and released to the atmosphere. Material that wasn’t instantly vaporized was thrown out of the crater (the ejecta) and was deposited to the northwest of the impact site
initial effects meteorite (sec->days)
close enough to the Yucatan Penninsula heard a sonic boom as body entered the atmosphere and then a detonation!
-A pulse of intense heat and light would move rapidly out from the impact site, vaporizing all close by and causing organic material, plants and animals to spontaneously combust farther away.
impact itself: caused the Earth to ring like a bell with seismic energy. A shockwave would move out from the impact site with superheated rock debris (including tektites) and molten material igniting fires (supported by the soot and subsequent fern and pollen data) and depositing a thick layer of ejecta in Mexico and the southern state
generated the largest tsunami probably ever seen in the history of Earth’s Biosphere.
what was Tanis
preserves a fantastic record of what happened in the minutes and hours proceeding the impact
remains river sys
believe that seismic waves from the impact may have triggered a ‘seiche’ (giant wave)* that rushed northward from the inland sea and up that river, only about 6 - 13 minutes following the impact.
wave would have thrown up and stranded many fish and marine creatures that were subsequently fossilized in the rock record from the area
1.How far away is Tanis from the impact site?
2.What is the evidence that the fossil fish at Tanis died within an hour of the impact and not due to the other effects that followed later?
3.How have some of the original spherules found at the site survived unaltered after so long?
4.What two kinds of rock fragments are found within the spherules?
5.What part of a dinosaur was found at Tanis and what tissue did it have preserved?
6.What kind of flying reptile egg was found at Tanis and what did it allow us to confirm about the morphology of the egg?
Longer-term (months to decades) effects of the impact
Changes in global temperature
Right after the impact millions of tons of dust/debris would thrown into the atmosphere, some very fine. stayed suspended, perhaps for months, cooling the Earth significantly but more importantly stopping plants from photosynthesizing in oceans/on land, leading to a sort of Cretaceous “nuclear winter” (a “Cold House”).
Eventually this fine dust would have cleared giving us our fine layer of iridium rich clay that marks the end of the Cretaceous.
Due to the death of so many plants during the “dark times”, the food chain would be in a severe state of collapse. Herbivores starved then carnivores.
dust had settled, water vapour would have remained in the atmosphere acting as a blanket, eventually fall as rain but greenhouse gas already released (CO2 from limestone vaporized)
hot house lasted yrs->decades
Changes in atmospheric composition: acid rain
burn” the air. In other words, you combine oxygen and nitrogen to form oxides of nitrogen which will eventually dissolve in water in the atmosphere to form a dilute nitric acid. This then falls out the air as acid rain
limestones in the Yucatan were associated with evaporites. Evaporites form when salts precipitate out of solution as the sun evaporates a body of water. Evaporite salts are often rich in the mineral Gypsum (CaSO4). When you vaporize gypsum you produce SO2 which combines with rainwater to produce sulfuric acid. In other words, even more acid rain that would poison soils and disrupt oceanic plankton
affect base food chain
what was the other impact that happened
the Nadir crator, off the west coast of Guinea and Guinea-Bissau in western Africa. This crator is 8.5km wide, meaning an asteroid of about 400 meters hit the African Coast sometime within a million years of the event in the Yucatan Peninsula.
1.How close in age are the Nadir and Chicxulub crators to one another?
2.How far from Chicxulub is the Nadir Crator?
3.What could finding the Nadir crator suggest about Earth’s orbit during this time?
4.Is it possible that there could be other undiscovered crators near this age that are yet to be discovered?
Deccan Traps
impact could not have been the only cause. In fact, the Earth has suffered impacts from space before with no associated appreciable mass extinction event
climate would have been affected by an increase in volcanic activity, in particular, during the formation of the Deccan Traps in India, which were highly active at this time. Like the Siberian Traps that occurred at the end of the Permian, this activity would have produced vast quantities of magma and gasses that could have seriously affected the Earth’s climate
The K/P Survivors
Chicxulub impact acted as the “final nail in the coffin”, taking an already “sick” biosphere further than it might have gone into a mass extinction event
generalists who did not require specific foodstuffs or particular environments to thrive
help if a creature were small enough to be able to hide or burrow away from the more severe environmental changes. On land, the plants that were best able to thrive after the mass extinction event were the angiosperms
creatures that were best able to adapt to these changes were the mammals. It is this group that radiates into the Cenozoic to take over the niches vacated by the non-avian dinosaurs
1.How important is the Amazon to the South American continent?
2.How diverse is the Amazon and what role do angiosperms play in this modern forest?
3.What did the community look like in the Amazon prior to the end-Cretaceous mass extinction?
4.Why did all major plant groups survive the end-Cretaceous mass extinction when many animal groups did not?
5.How did angiosperm diversity increase after the end-Cretaceous mass extinction when compared to the ferns and gymnosperm diversity?
6.What were the causes proposed for the turnover noted in Question 5?
7.What type of canopy forests exist today and what effect did that have on today’s Amazon Rainforest?
2.What was poisoning the Cretaceous atmosphere?
3.What effect did volcanic gas have on the reproduction of Tyranosaurus rex?
4.What was the early warning of the approaching Chicxulub asteroid that the dinosaurs might have witnessed?
5.Why did Anatotitan have to travel so far to find food?
6.What effect does the changing atmosphere have on Torosaurus herds?
7.Why are creatures with specialist life styles at risk during times of environmental stress?
8.Why does Didelphodon (an early marsupial mammal) have an advantage over specialists?
