8th Grade Science
Unit 8: Changes Over Time
Lesson 1: Natural Events
Contribute to Extinction
Vocabulary of Instruction
1. Mass Extinction
Theory For Mass Extinctions
• Mass extinction is
the process in which
a huge numbers of
species die out
suddenly.
• The dinosaurs (and
many other species)
became extinct,
probably because of
an asteroid that hit
the Earth.
1-B. Mass Extinction Theory
• This close-up
recreation shows the
fireball descending, a
large tidal wave rising
off the Yucatan
coast, the coastal
region being
inundated by the
ocean, and the
emergence of the
impact crater.
Mass Extinction in the Yucatan Peninsula
1-C. Mass Extinction Theory
• Although most
dinosaurs were
probably killed off in
the initial event
where returning
impact debris
superheated the
upper atmosphere,
the after events
would have been
very destructive too.
1-D. Mass Extinction Theory
• There would have been
huge tidal waves from
the shock, and possibly
the impact triggered
large earthquakes that
caused even more
extinctions.
• Afterwards, the upper
atmosphere would have
been saturated with
gases from the massive
fires, resulting in
years of climate
change that included
severe acid rain.
Mass Extinction Theory
Mass Extinction Theory
1-E. Mass Extinction
• Since life began on Earth, several major mass
extinctions have significantly exceeded the background
extinction rate.
• The most recent, the Cretaceous–Tertiary extinction
event, occurred 65 million years ago, and has
attracted more attention than all others as it marks the
extinction of nearly all dinosaur species, which were the
dominant animal class of the period.
• In the past 540 million years there have been five
major events when over 50% of animal species died.
• There probably were mass extinctions in the Archean
and Proterozoic Eons, but before the Phanerozoic there
were no animals with hard body parts to leave a
significant fossil record.
Mass Extinction Theory
1-F. Mass Extinction
• Estimates of the number of major mass
extinctions in the last 540 million years
range from as few as five to more than
twenty.
• These differences stem from the threshold
chosen for describing an extinction event
as "major", and the data chosen to
measure past biodiversity.
1-G. Mass Extinction Theory
Marine fossils are
mostly used to
measure extinction
rates because of their
superior fossil record
and stratigraphic
range compared to
land organisms.
2. Catastrophic Events
• Catastrophic events are
sudden, natural or manmade situations where
change and destruction
may occur without prior
knowledge or
preparation.
• Such occurrences may
limit normal functions in
daily living including
communications and
travel.
• Catastrophic Events
include the following:




Impact Events
Volcanic Eruptions
Tsunamis
Methane Hydrate
Eruptions
Man Made Catastrophic Events
2-A. Catastrophic Events
* Coming up on the right, you can
see the Meteor Crater, which is
a major tourist attraction in
northern Arizona.
* It was formed when a lump of
nickel and iron, roughly 150
feet in diameter and weighing
300,000 tons, struck the earth at
about 40,000 miles an hour,
scattering white-hot debris for
miles in every direction.
* The hole measures nearly one
mile across and is 570 feet
deep.
2-B. Catastrophic Events
Impact Crater Sites around the World
2-C. Catastrophic Events
• The tendency to discount
impact processes as a
factor in the Earth's more
recent geologic history was
severely challenged by the
interpretation in 1980 that
Cretaceous-Tertiary (K-T)
boundary sediments worldwide were due to a major
impact event and that
impact was the causal
agent for a mass
extinction event.
Impact Crater Sites in North America
The Day the Sands Caught Fire
A desert impact site demonstrates the
wrath of rocks from space