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For most of us, the Pyramids symbolize the distant past. After
all, they're more than 4,500 years old. But for geologists and
paleontologists, they might as well have been built yesterday.
That's because these biographers of the primordial deal in
increments of millions and even billions of years as they
struggle to reconstruct our planet's life history, which is so
vast that those 4,500 years would have to be replicated a
million times over to reach back to Earth's beginnings
4.5 billion years ago. Looked at another way, if one were to
measure our planet's age as a single 24-hour day, the first
human civilizations would appear less than a second before
midnight.
The geological time scale, established by scientists in the
mid-19th century and agreed upon internationally, breaks down
the eternity of our planet's history into more manageable
units than years. The scale functions as a massive calendar,
dividing the history of life into eras, periods, and epochs
based on fossil evidence. In this feature, explore the history
of life on Earth as we know it today, from the earliest
bacteria to the first modern humans. To launch the
interactive, click on
the image at left.—Lexi Krock
This interactive originally appeared on NOVA's
Missing Link Web site.
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