Eras of Earth's History

Question 1

Era

Answer 1

Geologists divide the time between the Precambrian time and the present into three long units of time called eras

Question 2

Period

Answer 2

Eras are subdivided into units of geologic time called periods.

Question 3

Geologic time scale

Answer 3

Record of the life forms and geologic events in earth’s history

Question 4

invertebrates

Answer 4

invertebrates are animals without backbones. during the Paleozoic era, invertebrates like jellyfish and worms drifted through the water, crawled along the sandy bottom, or attached themselves to the sea floor.

Question 5

Vertebrate

Answer 5

a vertebrate is an animal with a backbone. during the Ordovician era, the first vertebrate, the jawless fish, evolved.

Question 6

amphibian

Answer 6

an amphibian is an animal that lives part of its life on land and part of its live in water. during the Devonian period, animals began to invade the land. the first amphibian was the lungfish.

Question 7

Reptile

Answer 7

reptiles have scaly skin and lay eggs with tough, leathery shells. small reptiles started to develop during the Carboniferous Period.

Question 8

mass extinction

Answer 8

a mass extinction is when a large number of different species all become extinct at the same time. The mass extinction at the end of the Paleozoic affected both plants and animals, on land and in the seas.

Question 9

mammal

Answer 9

a mammal is a warm-blooded vertebrate that feeds its young milk. the first mammals that formed in the Triassic period where very small