the best science on the web about
geologic time

A Brief History of Life
 

A Brief History of Life

Scientists estimate Earth is 4.5 billion years old. In order to visualize and work with such an incredibly long history, geologists created a timeline.

The geological time scale is divided into era, period, and epochs — all punctuated with the important events found in layers of rock. Explore our planet's history from the earliest bacteria to modern humans.

NOVA/PBS
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The Ocean Throughout Geologic Time

The Ocean Throughout Geologic Time

Millions and millions of years ago ocean life-forms looked quite different from what you see today. Slide through time to witness some changes. More...

Images
Smithsonian
4 Ways to Understand the Earth’s Age

4 Ways to Understand the Earth’s Age

Consider Earth's history as a single calendar year — dinosaurs don't even appear until December! Take a look at this and three other ways to understand the mind-bending span of 4.5+ billion years. More...

Video
TED-Ed/Josh Sneideman
Rock Layers: Geological Time

Rock Layers: Geological Time

How exactly can layers of rock indicate geological time? This video explains how different layers of rock are formed and what you can tell by looking at them. More...

Video
Open University
The Grand Age of Rocks

The Grand Age of Rocks

How do geologists determine the ages of the rocks in the Grand Canyon, a park that covers over a million acres? Get the answer in this 'short primer on geologic dating methods." More...

Article
National Park Service
Zircon Chronology: Dating the Oldest Material on Earth

Zircon Chronology: Dating the Oldest Material on Earth

The mineral zircon is so durable it can survive geological events. Dive deeper into geochronology with this case study. More...

Article
AMNH
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Absolute Dating Rock Layers

Absolute Dating Rock Layers

It’s usually a given that the oldest rocks are on the bottom, but if scientists want actual dates, they choose the best absolute dating method. Take up the challenge for six layers of rock. More...

Interactive
University of Waikato
Geologic Eras Song

Geologic Eras Song

Have trouble remembering the geologic eras? This great, animated song will help remind you! More...

Video
MotionArt
Geologic Time Music Video

Geologic Time Music Video

What could possibly make geologic time more interesting? When it is explained with auto-tuning and smooth styling in this music video by The Script. More...

Video
Morgana Radelt and Mr. Parr
Geologic Time Quiz

Geologic Time Quiz

Are you ready to test your mastery of the geologic time scale? Put your knowledge to the test in this Glencoe quiz. More...

Interactive
Glencoe/McGraw-Hill
Geologic Time Scale

Geologic Time Scale

Journey through Earth's history with a click of your mouse. Jump to a time period in the graph and learn about its climate, geography, and life forms. More...

Interactive
Museum of Paleontology
How Do Geologists Know How Old a Rock Is?

How Do Geologists Know How Old a Rock Is?

Nothing beats radiometric dating when it comes to establishing the age of ancient things. But scientists also get clues from the way rocks are layered and from the fossils they contain. More...

Article
Utah Geological Survey
How We Discovered the Age of the Earth

How We Discovered the Age of the Earth

Even without radiometric dating, scientists began to figure out the vast age of the Earth, its species, and its rocks. Here's how they did it. More...

Article
Ars Technica
Life Through Time Mural

Life Through Time Mural

Explore all the different periods of geological time that paleontologists study in their work with this interactive mural. Click on the time period you're interested in: It's a cool way that art and science mix! More...

Interactive
Humboldt State University
Radiometric Dating: Playing Half-Life Odds

Radiometric Dating: Playing Half-Life Odds

When it comes to answering the question "How old is that rock?" scientists turn to radiometric dating. Roll the dice to get a hands-on look at how an isotope decays. More...

Activity
Science Buddies
Real Scientist: Carol Reiss

Real Scientist: Carol Reiss

Geologists explore the history of the Earth, just like historians, but instead of reading texts, geologists read rocks — called the geologic record. Find out what else geologists do in this profile. More...

Profile
DragonflyTV/PBS
Rock Sandwiches: Layering of Earth Particles

Rock Sandwiches: Layering of Earth Particles

Sedimentary rocks are the casserole of rock types, a bit of this and a dash of that, all crushed and baked into stone. In this hands-on experiment, you can show how sedimentary layers are formed. More...

Activity
education.com
The Interactive Geological Time Scale

The Interactive Geological Time Scale

Looking to see where a particular era, period, sub-period, or epoch fits in the geological time scale? This interactive is for you. More...

Interactive
American Geosciences Institute
What Is the Anthropocene and Are We in It?

What Is the Anthropocene and Are We in It?

The geologic time scale is organized around events that changed the Earth. Have human beings made such an impression on our planet that they mark a new geologic time period? Is this the end of the Holocene Epoch? More...

Article
Smithsonian

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