Earth’s history is divided into unequal time intervals. The boundaries between the intervals mark significant geological (very early Earth) or evolutionary events on Earth’s history. Example: The boundary between the Precambrian eon and the Phanerozoic eon is marked by the rapid evolution and diversification of organisms with hard body parts.ÂÂ
The time intervals are eons, which are subdivided into eras. The eras are subdivided into periods. The periods are further subdivided into epochs (not shown on figure).
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What is our current eon __, era ___, and period ___
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Age boundary between the Hadean eon and Archean eon ______
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Age boundary between Archean eon and Proterozoic eon ______
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Age boundary between Proterozoic eon and Phanerozoic eon ____
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Age boundary between Paleozoic era and Mesozoic era ________
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Age boundary between Mesozoic era and Cenozoic era ________
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What is the longest eon? _____
Duration of that eon ____
What percentage of Earth’s history is covered by that eon?
% = (Duration of Eon / Age of Earth) X 100
% = (_ / 4.65 billion) X 100
% = _
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What is the shortest eon? _______
Duration of that eon ____
What percentage of Earth’s history is covered by that eon?
% = (Duration of Eon / Age of Earth) X 100
% = (_ / 4.65 billion) X 100
% = _
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What is the longest era? _____
Duration of that era ____
What percentage of Earth’s history is covered by that era?
% = (Duration of Era / Age of Earth) X 100
% = (_ / 4.65 billion) X 100
% = _
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What is the shortest era? _______
Duration of that era ____
What percentage of Earth’s history is covered by that era?
% = (Duration of Era / Age of Earth) X 100
% = (_ / 4.65 billion) X 100
% = _
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What is the longest period? _____
Duration of that period ____
What percentage of Earth’s history is covered by that period?
% = (Duration of period / Age of Earth) X 100
% = (_ / 4.65 billion) X 100
% = _
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What is the shortest period? _____
Duration of that period ____
What percentage of Earth’s history is covered by that period?
% = (Duration of period / Age of Earth) X 100
% = (_ / 4.65 billion) X 100
% = _
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The suffix “zoic� is Greek for “life.� Which two eons do not have that suffix as part of their name?
What does the absence of the suffix suggests regarding life during those two eons? ____________________________________
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Notice the Figure does not subdivide the Hadean eon into eras (like the other eons). Taking into account the age of the eon, what will be the most likely reason for not doing era subdivisions? ___________________________
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The Phanerozoic eon is the eon of complex life (at least in terms that life moved from microscopic to macroscopic and involved the rapid evolution and diversification of organisms with hard body parts).
For how long has “complex� life existed on Earth? _____
How long did it take for it to first appear (Assume Earth’s age is 4.65 billion years)? _____
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The first evidence of life on Earth (a chemical signature of life) dates back to about 4 billion years. How long did it take for life to first appear on Earth (assume Earth’s age is 4.65 billion years)? __
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As we explore our neighboring planets, would it make sense to use the current Geologic Time Scale to explain/describe their geologic history? Why or why not?
The Correct Answer and Explanation is :
Let’s go through each of the questions in your query and I’ll provide you with the answers:
- Our current eon, era, and period:
- Eon: Phanerozoic
- Era: Cenozoic
- Period: Quaternary
- Age boundary between the Hadean eon and Archean eon:
- Approximately 4 billion years ago.
- Age boundary between the Archean eon and Proterozoic eon:
- Approximately 2.5 billion years ago.
- Age boundary between the Proterozoic eon and Phanerozoic eon:
- Approximately 541 million years ago.
- Age boundary between the Paleozoic era and Mesozoic era:
- Approximately 252 million years ago.
- Age boundary between the Mesozoic era and Cenozoic era:
- Approximately 66 million years ago.
- Longest eon:
- Hadean eon.
- Duration: Around 1 billion years.
- Percentage: (1 billion / 4.65 billion) * 100 ≈ 21.5%.
- Shortest eon:
- Phanerozoic eon.
- Duration: Approximately 541 million years.
- Percentage: (541 million / 4.65 billion) * 100 ≈ 11.6%.
- Longest era:
- Paleozoic era.
- Duration: About 290 million years.
- Percentage: (290 million / 4.65 billion) * 100 ≈ 6.24%.
- Shortest era:
- Cenozoic era.
- Duration: Approximately 66 million years.
- Percentage: (66 million / 4.65 billion) * 100 ≈ 1.42%.
- Longest period:
- Cambrian period.
- Duration: About 50 million years.
- Percentage: (50 million / 4.65 billion) * 100 ≈ 1.07%.
- Shortest period:
- Holocene period (Quaternary).
- Duration: Around 11,500 years.
- Percentage: (11,500 / 4.65 billion) * 100 ≈ 0.00025%.
- Two eons without the suffix “zoic”:
- Hadean eon
- Archean eon
- The absence of the “zoic” suffix suggests that life either did not exist or was in its most primitive, microscopic form during those eons.
- Reason for not subdividing the Hadean eon into eras:
- The Hadean eon predates the formation of life as we know it, and there was no significant geological activity that would warrant subdividing the eon into eras.
- For how long has “complex” life existed on Earth:
- Complex life has existed for approximately 541 million years, since the start of the Phanerozoic eon.
- Time it took for complex life to first appear:
- Complex life appeared around 541 million years ago, meaning it took approximately 541 million years from Earth’s formation (4.65 billion years) for complex life to emerge.
- First evidence of life on Earth:
- The first evidence of life (chemical signature) dates back about 4 billion years ago, so it took about 650 million years for life to first appear.
- Would the current Geologic Time Scale apply to other planets?
- It would not be entirely applicable because the Geologic Time Scale was created specifically based on Earth’s geological history, which includes events unique to our planet like the formation of the atmosphere and the appearance of life. Each planet would need its own time scale based on its specific conditions and history. For instance, Mars may have a different geological timeline due to its different atmosphere and lack of plate tectonics. The time scale could apply in a generalized sense (eons, eras, etc.), but the exact divisions would differ.
I will now generate an image summarizing these boundaries for you.
Here is a diagram of Earth’s geological time scale with the eons, eras, and periods clearly marked and labeled. It includes the time boundaries between these intervals, which should help in understanding the overall geological history. Let me know if you’d like any further details or adjustments!
