Geologic Time Scale
Eon
Era
Period
Mesozoic Era
Paleozoic Era
Phanerozoic Eon
Cenozoic Era
Neogene
Millions
of years
ago
Today –
23
Paleogene
23 –
65
Cretaceous
65 –
145
Jurassic
145 – 200
Triassic
200 – 251
Permian
251 – 299
Carboniferous
299 – 359
Devonian
354 – 417
Silurian
417 – 443
Ordovician
443 – 488
Cambrian
488 – 543
Proterozoic Eon
543 –
2,500
Archean Eon
2,500 –
3,800
Hadean Eon
3,800 –
4,570
Major biological events
The beginning of the Neogene is when the first hominids
(early humans) appeared. Modern humans appeared and
developed civilization by the end of this period. Mammoths,
sabre-toothed cats, and giant camels dominated until
10,000 years ago when many large mammals went extinct.
Rise of the mammals and birds. Rodents, primates, pigs,
cats, dogs, bears and whales appear. Flowering plants
spread across the globe.
Dinosaurs continue to dominate the land. Marsupials,
modern sharks, bees and butterflies appear. Flowering
plants appear. Period ends with the mass extinction of the
dinosaurs and many plants.
Dinosaurs dominate the land. Mammals are common but
small. Feathered dinosaurs and birds appear. The most
common land plants are ferns, palm-like trees called
cycads, and grasses.
The few survivors of the Permian extinction go on to
populate the land and oceans. New species like mammals,
dinosaurs and crocodiles appear.
Amphibians dominate the land. Early cone-bearing plants
like pine trees appear. Period ends with the largest mass
extinction known with 95% of all marine species and 50%
of all animals going extinct.
Many swamps on land and sponge reefs in the oceans.
Reptiles appear. Early winged insects and cockroaches
appear.
Fish spread across the oceans. Amphibians appear. The
first trees and other plants spread across the land creating
the first forests.
Spiders, scorpions, insects, complex plants, and fish with
bony jaws appear. Fish adapt to living in rivers and fresh
water for the first time.
First land plants appear. Primitive fungi and sea weed
appears. The oceans are full of corals, mollusks, worms,
primitive fish, and echinoderms like starfish.
A large number of new animal species appear in a relatively
short time. First fish appear. No known life on land yet.
First multi-celled organisms like sponges appear. Earliest
complex life forms are algae from 1.4 billion years ago.
Oxygen begins to accumulate in the atmosphere.
Earliest life on Earth are bacteria from 3.5 billion years ago.
Earth is very different from today. The atmosphere is
mostly methane and ammonia. The continents only just
have begun to form.
No known life. The Earth’s crust cools and solidifies. The
moon forms.
Assembled from the International Commission on Stratigraphy 2004 report A Geologic Time Scale and from information on the
Univeristy of California Museum of Paleontology website (http://www.ucmp.org). This work is licensed under the Creative
Commons Attribution-NonCommercial License. To view a copy of this license, visit http://creativecommons.org/licenses/bync/2.5/ or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.
Constructing a Geologic Time Line
Introduction:
The goal of this activity is to visualize the geologic history of the earth by making a geologic time line.
Materials:
 Meter stick
* 5 m adding machine tape or other paper
* pencil
* colored pencils
Procedure:
1. For this procedure, the scale is 1 mm = 1 million years, or 1 m = 1 billion years.
2. Measure out 5 meters of adding machine tape. Draw a horizontal line all the way down the middle of
the tape representing your time line.
3. Label the starting end “Present.” Make a mark at 1 meter and label it “1 billion years ago,” 2 meters “2
billion years ago” and so on till you reach 5 meters.
4. Plot each geographic period on your timeline using the handout “Geologic Time Scale.” Label the
name of the period.
5. Below each period title write a brief description of what happened during this time. For example,
under Neogene you might write “Humans appeared.”
6. Color in your timeline by making each era a different color.
Analysis questions:
1. How many years does 1 cm represent on this scale? ___________
2. The __________________________ is an outline of the major events in the earth's history. The largest
grouping of time is a __________________. The next largest grouping of time is a
__________________.
3. The first mammals appeared during the _________________ period in the __________________ era
and ___________________eon.
4. Which time period is the longest? ______________________
5. Which time period is the shortest? ________________________
6. In which period did humans exist or begin to exist? ____________________
7. In which era did dinosaurs exist or begin to exist? _____________________
8. In which eon did life exist or begin to exist? _____________________
9. Which has lived on the earth the longer time, dinosaurs or mammals? ____________________
10. What surprised you about this timeline?
Assembled from the International Commission on Stratigraphy 2004 report A Geologic Time Scale and from information on the Univeristy of
California Museum of Paleontology website (http://www.ucmp.org). This work is licensed under the Creative Commons Attribution-NonCommercial
License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc/2.5/ or send a letter to Creative Commons, 559 Nathan
Abbott Way, Stanford, California 94305, USA.