Name:_________KEY__________________________ Date:___________________ Period:__________

GEOLOGIC TIME SCALE REFLECTION

1) Use relative age dating to sequence these events: first land plants, first reptiles, mammals dominate, trilobites plentiful, Pangea forms, first fishes, series of ice ages, first amphibians, single-celled organisms appear, dinosaurs diversify

Oldest __single-based organisms__, _trilobites plentiful_, ___first fishes___, _first land plants____,

____first amphibians___, _first reptiles______, __Pangea forms_____, ___dinosaurs diversify___,

____mammals dominate_______, ___series of ice ages______________ . Most Recent.

2) Briefly describe the progression of life from the end of the Precambrian Time (Proterozoic Eon) to current day. Highlight the significant changes in dominate life forms from one era to the next?

Precambrian: Single-celled to multicellular (extinction)

Paleozoic: invertebrate to vertebrate to fish to amphibians to reptiles (extinction of many marine invertebrate, including trilobites)

Mesozoic: dinosaurs to warm-blooded reptiles to birds (mass extinction caused disappearance of many land and marine life forms, including dinosaurs)

Cenozoic: mammals to humans (giant mammals such as mammoths become extinct with Ice Age)

3) Read pg. 340 “Earth's Surface Forms” & “Life Develops” (blue textbook) Precambrian Time extended for 90% of Earth's history. Describe the environmental conditions/events of Precambrian Time. How does Precambrian Time differ from era that follow it (why do some geologic time scales leave the majority of PT out of the time scale)?

New atmosphere formed of carbon dioxide, water vapor, and nitrogen – volcanic eruptions released carbon dioxide, water vapor, and other gases

Earth's surface cooled, water vapor began to condense to form rain and eventually formed oceans

more and more of Earth's rock cooled and hardened – less dense rock formed large landmasses

life is just getting started and developed in Precambrian time – it isn't until the Paleozoic do we see a great “explosion” of invertebrate life

Paleozoic era really sees lifeforms develop from invertebrates to vertebrates to fish to amphibians to reptiles

Geologic events include coral reefs developing, mountains form, deserts, and Pangaea

4) If you had to come up with a title to describe the 4 major time periods, what title would you give each period?

Precambrian	Paleozoic	Mesozoic	Cenozoic
The Beginning	Explosion of Life (invertebrates to reptiles)	Age of Reptiles/Dinosaurs	Age of Mammals

5) Read pg. 345 (blue textbook) “Mass Extinction Ends the Paleozoic, The Supercontinent Pangea & pg. 351 “Another Mass Extinction.” How do you view mass extinctions? Describe the role you think mass extinctions played in Earth's history.

Mass extinctions affect both plants and animals, on land and in the seas. Mass extinctions seemed to be linked to huge changes in climate. Because the environment is restructured, allows organisms to adapt and evolve to current conditions. For example, the biggest change in sizes of organisms over geologic time happened when the amounts of oxygen in the atmosphere also increased.

6) The Phanerozoic Eon is divided into 3 eras (Paleozoic, Mesozoic, and Cenozoic).

a) State the major change at the end of era. In other words, which event ended both the Paleozoic and Mesozoic eras?

Paleozoic: mass extinction caused by continental drift and climate change - formation of Pangea caused deserts to expand in the tropics – at the same time, sheets of ice covered land closer to the South Pole (many organisms could not survive the new climate)

Mesozoic: mass extinction caused by climate change from asteroid impact and volcanic activity. Photosynthesis could not occur because large amounts of dust blocked sunlight around the world.

b) Now, predict the cause and type of change that might end the Cenozoic era.

A mass extinction caused by climate change

Danae Whitaker

2014-04-10