Lesson 37 Causes of Extinction
Extinction and its effects
Extinctions occur naturally over time. Extinctions occur after a sudden, drastic change in the
environment. Populations may not be able to adapt to survive the change.
Natural Causes of Extinction
99.9% of all species that ever existed have gone extinct. An average species survives 2 to 10
million years. All species experience changes in their environment where they cannot adapt.
The following events can cause extinction: change in temperature or rainfall, volcanic
eruptions, earthquakes, floods or drought, changes in food supply and a new predator or disease.
P 248
Mass Extinctions
Mass Extinctions occurs when large numbers of species die out in a short period of time.
During these events more than 50% of all species died. Abundant fossils in the rocks disappear
and fossils of many new species begin to appear.
65 million years ago dinosaurs disappeared from earth. Cooling of earth’s climate and a
decrease in photosynthesis caused the extinctions.
P 249
The Asteroid Theory
Some scientists believe that the dinosaur extinction was due to the impact of a giant asteroid.
Evidence of the asteroid is in the K/T rock layer where they find iridium which is found in
meteorites. Clouds would have blocked out the sunlight causing earth to cool and plants to die.
Gradual Theory
Movement of tectonic plates and increase in volcanic activity may have caused climate change.
They think that volcanic eruptions blocked out the sun, caused cooling and plants to die. They
think the lava had iridium in it.
Mass Extinctions and New Species
After extinctions surviving species evolve and adapt.
Humans and Extinctions
An increase in the rate of extinctions has been tied to activities of humans. Habitat destruction,
pollution, and overfishing can lead to extinction of plant and animal species. Some remedies
include land management, protect native species, reduce pollution, and to reduce demand for
products.
Lesson 37 Causes of Extinction
Extinction and its effects
Extinctions occurs ______________________ over time. Extinctions occur after a sudden, drastic change in
the ______________________. Populations may not be able to ______________________ to survive the
change.
Natural Causes of Extinction
99.9% of all species that ever ______________________ have gone extinct. An average species survives
______________________ to 10 million years. All species experience ______________________ in their
environment where they cannot adapt.
The following events can cause extinction: change in ______________________ or rainfall, volcanic
eruptions, earthquakes, ______________________ or drought, changes in ______________________ supply
and a new predator or disease.
(P 248)
Mass Extinctions
Mass Extinctions occurs when ______________________ numbers of species ______________________
out in a short period of time. During these events more than 50% of all species died. Abundant
______________________ in the rocks disappear and fossils of many ______________________ species
begin to appear.
65 million years ago dinosaurs ______________________ from earth. Cooling of earth’s
______________________ and a decrease in photosynthesis caused the extinctions.
(P 249)
The Asteroid Theory
Some scientists believe that the dinosaur extinction was due to the impact of a giant
______________________. Evidence of the asteroid is in the ______________________ rock layer where
they find iridium which is found in ______________________. Clouds would have blocked out the
______________________ causing earth to cool and plants to ______________________.
Gradual Theory
Movement of tectonic plates and increase in ______________________ activity may have caused climate
change. They think that ______________________ eruptions blocked out the ______________________,
caused cooling and plants to die. They think the ______________________ had iridium in it.
Mass Extinctions and New Species
After extinctions surviving species ______________________ and adapt.
Humans and Extinctions
An increase in the rate of extinctions has been tied to activities of ______________________. Habitat
destruction, ______________________, and ______________________ can lead to extinction of plant and
animal species. Some remedies include ______________________ management, protect native species,
reduce ______________________, and to reduce demand for products.