The past 20000 years when a vast number of large

the past 20,000 years, when a vast number of large mammal species vanished from North
America
 More efficient competitor appears, steals ecological niche from the weaker species, whose
members can’t obtain enough food to survive.
Mass extinction events:
 Late Paleozoic Era came to a close:
o Permian-Triassic extinction: due to eruption of 3 million cubic km of basalt in Siberia

o 95% of marine species disappeared
o Terminal Permian mass extinction occurred as a result of extraordinary volcanic activity
in Siberia, basalt sheets extruded during the event
o Eruptions could have clouded the atmosphere, acidified the oceans, and disrupted the
food chain
 K-T boundary event:
o Cretaceous-Tertiary extinction: due to a giant meteorite impact near the Yucatán
peninsula in Mexico
o End of Cretaceous Period, 65 million years ago
o Dinosaurs which had ruled the planet for over 150 million years, simply vanished, along
with 90% of plankton species in the ocean, and up to 75% of plant species
o Huge meteorite impact, generated 2-km-high tsunamis that inundated the shores of
continents and generated a blast of hot air that set forests on fire, blast could have
ejected so much debris that for months there would have been perpetual night and
winter-like cold
o The Chicxulub impactor, also known as the Chicxulub asteroid, was an asteroid 10 to 15
kilometres in diameter which struck the Earth at the end of the Cretaceous,
approximately 66 million years ago, creating the Chicxulub crater
o It impacted a few miles from the present-day town of Chicxulub in Mexico, after which
the impactor and its crater are named
o Because the estimated date of the object's impact and the Cretaceous–Paleogene
boundary (K–T boundary) coincide, there is a scientific consensus that its impact was the
Cretaceous–Paleogene extinction event which caused the death of most of the planet's
non-avian dinosaurs and many other species
o The impactor's crater is just over 177 kilometers in diameter, making it the third largest
known impact crater on Earth
Megathrust earthquakes
 Occurs in subduction zones where two crustal plates are colliding
 Most subduction zones occur where an oceanic plate is being forced beneath a continental plate
 Large sections of the two plates become locked together, stress in the rocks builds up storing
energy in the rocks until they break, creating great earthquakes that are often magnitude 9.0 or
higher
 Since 1900 there have been five magnitude 9.0 or greater earthquakes, all these events were
subduction zones

Measuring Earthquake Size:
 Energy released can be calculated:
o M
w
6.0 – equivalent to the energy of the Hiroshima atomic bomb
o M
w
8.3 – equivalent to energy of the 1961 Tsar Bomba
o An increase of one step in M
w
is equivalent to a 32x increase in energy
1960 Great Chilean Earthquake “Valdivia Earthquake” (M
w
9.5)
 May 22
nd
, 1960
 The 1960 Chilean earthquakes were a sequence of strong earthquakes that affected Chile
between May 21 and June 6 1960
 The first was the 8.1 M
w