1.5.5 Mass Extinctions: An Asteroid Can Ruin Your Day

Question 1

mass extenctions

Answer 1

• There are five distinct mass extinctions where the number of taxonomic families drops sharply.
• occur at the end of the Ordovician, Devonian, Permian, Triassic, and Cretaceous time periods.

Question 2

notes

Answer 2

• Much of the fossil record reflects a slow evolutionary change.
• Evolutionary biologists are still debating the cause of these events

Question 3

Ordovician period

Answer 3

• characterized by a massive glaciation event. The glaciers resulted in a drop in ocean temperature and
  level (50 meters). Eighty-five percent of the species (all of which were marine) became extinct.
• 500-440 million years ago

Question 4

Devonian flora and fauna

Answer 4

• consisted of marine and early land organisms such as
  cephalopods, jawed fish, amphibians, scorpions, spiders, and land plants. Scientists think that a continental collision caused a drop in ocean temperature. Eighty percent of marine species were wiped out.
• 400-345 million years ago

Question 5

Permian extenction

Answer 5

• Giant insects and a variety of reptile species characterized the Permian time period. The supercontinent Pangea formed and most of
  the land mass was subject to cold temperatures. Glaciers and volcanoes were prevalent. Ninety percent of land and marine species were wiped out.
• 290-245 million years ago
• age of insects
• reptiles

Question 6

Triassic extenction

Answer 6

• During the Triassic, giant reptiles and gymnosperms flourished. Seventy-five percent of the species went extinct, possibly because of a meteor impact.
• 240-210 million years ago

Question 7

Cretaceous extinction

Answer 7

• Before the Cretaceous extinction, mammals comprised a relatively small fraction of the taxonomic families. Dinosaurs comprised a large portion of taxonomic families. Seventy five percent of vertebrates larger than 25 kilograms were wiped out. The extinction probably resulted from a meteor impact. A
  layer of iridium, an element that is rare on earth but common in meteorites, is found between Cretaceous and Tertiary sediments
• 65 million years ago

Question 8

Scientists think that a continental collision resulted in a mass extinction during which period?

Answer 8

• devonian

Question 9

The cause of the mass extinctions of marine species at the end of the Ordovician period is thought to be

Answer 9

• massive glaciation

Question 10

Why is an iridium-rich layer of rock significant in evidence bearing on the Cretaceous–Tertiary extinction?

Answer 10

• Iridium is rare on earth but common in extraterrestrial rocks.

Question 11

The fossil record tells us that mass extinctions occurred because

Answer 11

• there are periods during which there is a sharp decline in the number and types of fossils found.

Question 12

During what period did the dinosaurs suddenly disappear from the record?

Answer 12

• Cretaceous, 65 million years ago

Question 13

Which of the statements regarding the Permian time period is incorrect?

Answer 13

• The earth was populated by small mammals

Question 14

The prevailing theories about mass extinction are that the causes may have been

Answer 14

• glacier formation, meteorites crashing into the earth, and movement of continents

Question 15

Which of the following is true about the mass extinction that occurred during the Ordovician period?

Answer 15

• Eighty-five percent of the species (all of which were marine) were wiped out.