TOPIC 2: Case study, the K/T extinction
1. K/T Extinction
• Describe the character of extinctions at the K/T boundary
The K/T extinction is also known as “The Dinosaur Killer”. In this period at least 50% of all species were lost and basically,
anything nothing over 25 kg survives. This era affected not only terrestrial species but also marine fauna such as ammonites
and marine reptiles. 80-90% marine species were lost.
The Cretaceous biosphere was already stressed and the K/P impact was “the final nail in the coffin”. The impact was
probably THE causal factor in extinction of the dinosaurs.
• Discuss the evidence used to support the K/T impact
Luis and Walter Alvarez (Father and Son) discovered that the latest Cretaceous clay layers found all over the world contain a
concentration of iridium many times greater than normal. Given that iridium is rare in the Earth’s crust and that they are
mostly found in asteroids and comets, Alvarez team suggested that an asteroid struck the Earth at the time of the K-Pg
boundary. This is asteroid landed on the coast of Yucatan, Mexico causing global firestorms that may have resulted as
incendiary fragments from the blast fell back to Earth.
Fern spores vs. pollen: ferns were the first ones to become fire-impacted landscape and spores act as a proxy for
forests fires. After K/P, there was a massive spike in fern spores thus, supporting the idea of several forest fires
occurring during the asteroid impact.
Soot layers associated with the iridium layer: the soot layers found in this era suggests the existence of massive global
fires. These are also found in the iridium layer suggesting a link between both.
Tektites: tektite is a natural gas that is produced by the melting of rocks during an impact. There were very common
in the K-Pg boundary providing further evidence of a correlation.
Shocked Quartz: This is another “impact” feature that are commonly found in the K-Pg boundary. This quartz will be
deformed when under pressure or strong impact. “Cross-hatched” lines will be shown as lines of stress. These
deformations are also called shock lamellae and are only seen under the microscope.
Tsunami deposits: there’s evidence of deposits of an almost global tsunami at the end of Cretaceous that could be
formed by the asteroid impact.
• Describe the location and probable nature of the K/T impactor
When drilling in the coast of Mexico at the Yucatan Peninsula, they found the existence of “odd” rocks such as melted rocks
and suevite. Suevite is a breccia (fracture rock) that shows further evidence of melting rocks. They remained there until
geophysics reveals that the asteroid impact left a crater called Chicxulub (also called “The Smoking Gun”). This crater is
180km across and they found evidence such as tsunami deposits, shocked quartz and tektites that was richer towards the
crater. Chicxulub, meaning “Tail of the Devil” is of shallow entry (20-30 degrees) and the impact body is of 10 km across.
Ejecta is debris ejected during the formation of an impact crater. In this case, the ejecta is mostly blown towards NW. 100km
of rock was vaporized and 6.2 X 10 tonnes exploded.
• Describe the initial and long-term effects of the impact and their environmental consequences
Vaporization of everything that was close
Order of a succession of ocean rocks that crosses the K/P boundary about 100km from the impact site:
Normal ocean sediments – Ejecta – Tsunami sediments – Clay/Iridium – Normal ocean sediments
Sunlight shut off – there was a nuclear winter that lasted anywhere from weeks to several months.
With no sunlight, photosynthesis stopped on land and oceans
Water vapour remained in the atmosphere and Yucatan limestones vaporization increased the greenhouse gases and
as a result the average global temperature rose up to 10 degrees Celsius. There was a rapid shift from cold (several months) to hot (several years)
High-energy blast in where nitrogen and oxygen combined with water vapor. Acid rain was produced acidifying
oceans and soil land.
Yucatan evaporites appear: salts precipitated by evaporating bodies of water.
Everything turned into salt creating the Salt Flat or Death Valley in The Mediterranean.
A week of acid rain was produced by the evaporation of minerals such as Gypsum that is rich in sulfates. This hit base
in oceans and land damaging the lowest level of the food chain.
• Consider other potential causes of the K/T environmental collapse
India: acid rain
Climatic greenhouse effects
Continued environmental degradation related to the breakup of Pangea
Many species already going into extinction
Deccan Traps Flood Basalts: large igneous rocks located on the Deccan Plateau of west-central India and one of the
largest volcanic features on Earth. It was an area of intense basaltic volcanic activity at the end of the Cretaceous
thought to have serious consequences for the health of the biosphere.
TOPIC 3: Impacts
1. Our place in the solar system / galaxy
• Describe the type and location of potential impactors and rate of meteoroid influx
1. Comets or “dirty snowballs”
a. Commonly around 15km of diameter
b. They come from the Oort Cloud and Kuiper Belt (Kuiper Belt is inside the Oort Cloud)
c. They have tails that are formed by solar winds that sublimes ice
d. Tails “fall” into the inner solar system as they crossed the Earth’s orbit. The tails are always directed away
from the sun and they get longer as they come closer to the Sun.
i. Comet Hayley: 74 -79 years ago
ii. Comet Hale-Bopp: in 1997 and will be back again in 2380 years
f. Leonid Meteor Shower happens every November
g. The tail of Comet Tempel- Tuttle comes back every 33 years
h. Meteorite: an object that survives impact with Earth’s surface. They create a “band” of meteoroid debris.
a. Smaller than planets but larger than meteoroids
b. They are common in a series of belts between Mars and Jupiter
Rates of meteoroid influx:
100 000 million every 24 hours.
Most burn up entirely 60km above surface