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Life and the Geologic Time Scale

Major events in the evolution of life are used to divide up the geologic time scale.

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The History of Life in 24 Hours

The History of Life in 24 Hours

Credit: Woudloper
Source: http://en.wikipedia.org/wiki/File:Geologic_Clock_with_events_and_periods.svg
License: CC BY-NC 3.0

Do you get impatient standing in line in the cafeteria? Well, your entire life is so far accounts for only 0.000000267% of Earth history? In the diagram above, it’s not even a tiny point. So that time you spend in line? Well, that isn’t so much after all.

Amazing But True!

It’s really hard to understand how old Earth is. There’s just no way to make it seem real. One way scientists try is to compress earth history into something understandable, like a 24-hour day. Our planet formed 4.5 billion years ago; let’s call that midnight. Make the current time is midnight the following day. You may be surprised at how this goes!

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With the links below, learn more about the evolution of life on Earth. Match up the organisms in the NOVA interactive with the timeline in the Asap SCIENCE video. Then answer the following questions.

  1. If Earth forms at midnight, at what time does the first life appear? When are the first eukaryotes? When is the first multicellular life?
  2. What is the Cambrian explosion? What are some of the life forms that roam the seas?
  3. At what time do plants and animals begin to colonize the land?
  4. What happened in the Cretaceous Period? When was the mass extinction that ended the reign of the dinosaurs?
  5. When do humans emerge? How long is all recorded history? How long has your life been?

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Image Attributions

  1. [1]^ Credit: Woudloper; Source: http://en.wikipedia.org/wiki/File:Geologic_Clock_with_events_and_periods.svg; License: CC BY-NC 3.0

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