Mass Extinctions

Geologic Time Scale

7th Grade Science

Geologic Time Scale

• A record of the major events and diversity of life forms in Earth's history

• Began when Earth was formed and goes on until the present day

• Eons ----> Eras ----> Periods

Multiple Choice

Paleozoic, Mesozoic & Cenozoic are all ________.

• Epochs

• Eras

• Periods

• Eons

Time Scale Events

• At the end of each era, a mass extinction occurred

• Although there were other extinctions going on during each period of geologic time

Multiple Choice

Describe how geologists separate time periods.

• By special events that have happened in that period.

• By looking at the Relative Time of a Fossil

• By counting the years a fossil has been preserved

• By the animals in the time period.

The Fossil Record

• Using the fossil record, paleontologists have created an idea of the different types of common organisms in each geologic period

• Ex: Mammals appear in Mesozoic era ---> Cenozoic era

Precambrian Era

• Earth's first era of time

• Began 4.6 mya: Creation of Earth

• Began with simple life forms such as bacteria and simple algae

• A rise of simple organisms such as jellyfish and sea worms by the end of the era

• Few fossils from era

Era Major Events

• 1. Formation of Sun & light

• 2. Creation of the Earth

• 3. Creation of atmosphere through volcano out-gassing

• 4. Creation of oceans

• 5. Creation of life

Multiple Choice

How old do Paleontologists believe the Earth is?

• 2021 years old

• 4.6 million years old

• 4.6 billion years old

• 3.6 billion years old

Paleozoic Era

• Began with the early invertebrates (trilobites and brachiopods) --> early vertebrate fish --> arachnids and insects ---> first amphibians --> reptiles became dominant near end

• Early land plants included simple mosses, ferns, and then cone-bearing plants

• By the end of the era, seed plants were common

Era Mass Extinction

• The mass extinction that ended the era caused most marine invertebrates as well as amphibians to disappear

Mesozoic Era

• Reptiles were the dominant animals of this era, including dinosaurs

• Small mammals and birds appeared

• Toward the end of the era, flowering plants appeared and the kinds of mammals increased

Era Mass Extinction

• The mass extinction that ended the era caused the dinosaurs to become extinct

Open Ended

What animal group dominated the Mesozoic era?

Cenozoic Era

• New mammals appeared while others became extinct

• The diversity of life forms increased

• Flowering plants became most common

• Humans are also part of the most recent period of this era

Open Ended

What animal group has dominated the Cenozoic era?

Multiple Choice

Name the 4 time frames in order from oldest to youngest.

• Precambrian Time, Paleozoic Era, Mesozoic Era, Cenozoic Era

• Mesozoic Era, Precambrian time, Cenozoic Era, Paleozoic Era

• Paleozoic Era, Mesozoic Era, Precambrian Time, Cenozoic

Multiple Choice

The time span that lasted the longest was the...

• Precambrian

• Mesozoic

• Paleozoic

• Cenozoic

Open Ended

What era are we living in now?