Age of Earth
Dana Desonie, Ph.D.
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Printed: October 2, 2014
AUTHOR
Dana Desonie, Ph.D.
www.ck12.org
C HAPTER
Chapter 1. Age of Earth
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Age of Earth
• Understand the evolution of life on Earth in a more easily comprehended time scale.
What is deep time?
We can look so far out into space that it’s hard to imagine the distances. We also have trouble imagining the extend
of geologic time. This section might help.
Age of Earth
Earth scientists use radiometric dating, index fossils, and other clues. They have determined that Earth is 4.6 billion
years old. The planet is the same age as the rest of the solar system.
Geologic Time Condensed to One Year
It’s always fun to think about geologic time in a framework that we can more readily understand. Here are when
some major events in Earth history would have occurred if all of Earth history was condensed down to one calendar
year.
January 1, 12:00 am: Earth forms from the planetary nebula –4600 million years ago
February 25, 12:30 pm: The origin of life; the first cells –3900 million years ago
March 4, 3:39 pm: Oldest dated rocks –3800 million years ago
March 20, 1:33 pm: First stromatolite fossils –3600 million years ago
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July 17, 9:54 pm: First fossil evidence of cells with nuclei –2100 million years ago
November 18, 5:11 pm: Cambrian Explosion –544 million years ago
December 1, 8:49 am: First insects –385 million years ago
December 2, 3:54 am: First land animals, amphibians –375 million years ago
December 5, 5:50 pm: First reptiles –330 million years ago
December 12, 12:09 pm: Permo-Triassic Extinction –245 million years ago
December 13, 8:37 pm: First dinosaurs –228 million years ago
December 14, 9:59 am: First mammals –220 million years ago
December 22, 8:24 pm: First flowering plants –115 million years ago
December 26, 7:52 pm: Cretaceous-Tertiary Extinction –66 million years ago
December 26, 9:47 pm: First ancestors of dogs –64 million years ago
December 27, 5:25 am: Widespread grasses –60 million years ago
December 27, 11:09 am: First ancestors of pigs and deer –57 million years ago
December 28, 9:31 pm: First monkeys –39 million years ago
December 31, 5:18 pm: Oldest hominid –4 million years ago
December 31, 11:02 pm: Oldest direct human ancestor –1 million years ago
December 31, 11:48 pm: First modern human –200,000 years ago
December 31, 11:59 pm: Revolutionary War –235 years ago
Source: http://www.timetoast.com/timelines/63215
Watch the following video for another analogy of geologic time: Richard Dawkins Plays the Piano - Earth History
in C Major at http://www.youtube.com/watch?v=29nXWYEx_js (1:03)
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/4802
Summary
• Earth is 4.6 billion years old. It is also 4,600 million years old.
• If Earth history is equal to a year, all of human history has taken place in the last 12 minutes.
• The Cambrian Explosion took place on November 18. Life is very recent.
Practice
Use the resource below to answer the questions that follow.
• 4.6 Billion Years in the Making: Our Wonderful World at http://www.youtube.com/watch?v=9Ra9lwKn7
5s (3:47)
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Chapter 1. Age of Earth
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/58894
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When did Earth form in years ago and on the one year calendar?
When did the first life appear in years ago and on the one year calendar?
When did multicellular life evolve in years ago and on the one year calendar?
When did the first plants evolve in years ago and on the one year calendar?
When did the dinosaurs go extinct in years ago and on the one year calendar?
When were the Himalayas formed in years ago and on the one year calendar?
When did the first humans appear in years ago and on the one year calendar?
When was the end of the last ice age in years ago and on the one year calendar?
Review
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How old is Earth?
What was the longest major stage in the history of life and what was it?
When did modern humans arise in Earth history?
When did the cell nucleus evolve?
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