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Age of Earth

Scientists have tried to determine Earth's age in various ways over time; we now know that Earth is about 4.6 billion years old.

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Age of Earth

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

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.


  • 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.


  1. How old is Earth?
  2. What was the longest major stage in the history of life and what was it?
  3. When did modern humans arise in Earth history?
  4. When did the cell nucleus evolve?

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Use the resource below to answer the questions that follow.

  1. When did Earth form in years ago and on the one year calendar?
  2. When did the first life appear in years ago and on the one year calendar?
  3. When did multicellular life evolve in years ago and on the one year calendar?
  4. When did the first plants evolve in years ago and on the one year calendar?
  5. When did the dinosaurs go extinct in years ago and on the one year calendar?
  6. When were the Himalayas formed in years ago and on the one year calendar?
  7. When did the first humans appear in years ago and on the one year calendar?
  8. When was the end of the last ice age in years ago and on the one year calendar?

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