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 Life evolves.
Everything on Earth that has ever lived is connected through, and is the result of, evolution. It’s a process that’s been happening since the first tiny life forms appeared some four billion years ago.
Our story begins with our understanding of time.
The Earth is around 4.5 billion years old. To help organize and understand this immense expanse of time, scientists divide Earth’s history into smaller chunks, such as eras and periods. Together, these make up the geologic time scale.
Think of the geologic time scale as the table of contents in the history of Earth. The eras and periods are chapters in the story of evolution. Each chapter has its own tale to tell—when life began, when mammals first appeared, when humans entered the scene.
To begin your tour through time, select a chapter from the descriptions below. The geologic time scale on your right will help you keep track of where you are in time.
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Precambrian:
Learn about how life first began on our planet, and view amazing meteorites and specimens that help explain the origin and early evolution of life.
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Cambrian / Ordovician:
Witness the explosion of life that happened in Earth’s oceans during this time, and see spectacular specimens of early aquatic animals.
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Silurian / Devonian:
Discover the trailblazing plants that transformed Earth’s barren landscape, and meet fishes and tetrapods—the first four-limbed animals with backbones to crawl from the sea to shore.
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 Carboniferous:
Check out the great tropical forests that once blanketed our planet—and gave Illinois its huge coal reserves. You’ll meet Illinois’s state fossil, the Tully monster, and other spectacular Carboniferous specimens from Mazon Creek, Illinois’s most famous fossil site.
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Permian:
Explore Pangaea, the giant supercontinent that was home to the first reptiles and synapsids (the group that today includes mammals).
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Mesozoic:
Enter the Age of Dinosaurs, view dozens of fabulous fossils of these ancient giants, and uncover the events that led to their extinction.
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Tertiary:
Move on to the Age of Mammals and learn about how changing climates and continents affected the evolution of familiar species, including horses, whales, dogs, and cats.
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Hominids:
Meet the first humans and trace our evolution from our early ape ancestors. You’ll learn about the unique characteristics that set us apart from our closest primate relatives.
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Quaternary:
Examine our most recent—and still ongoing—ice age. Check out some of the most well-preserved fossils of this period, found at California’s La Brea tar pits, and learn about the mass extinction facing many of today’s species.
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Continue to the Precambrian. >>
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