College

Refer to Figure 8-1. Note that the formation of the Earth occurred 4.56 billion years ago.

1. Calculate the percent of geological time represented by the Hadean.
2. Calculate the percent of geological time represented by the Archean.
3. Together, what percent of geological time is represented by the combined span of the Hadean and Archean?
4. If we think of geological time as a 24-hour clock, and the Earth formed at midnight, what time of day did the Archean end? Give your answer in hours and minutes (no need for seconds).

Answer :

The percent of geological time represented by the Hadean is calculated as follows:

  • (0.56 billion years / 4.56 billion years) * 100 = 12.3%

The percent of geological time represented by the Archean is calculated as follows:

  • (1.5 billion years / 4.56 billion years) * 100 = 33.0%

The combined span of the Hadean and Archean periods represents the following percent of geological time:

  • (2.06 billion years / 4.56 billion years) * 100 = 45.3%

If we think of geological time as a 24-hour clock, with the Earth forming at midnight, the Archean period would end at approximately:

  • (33.0 / 100) * 24 hours = 7.92 hours

So, the Archean period would end at around 7:55 AM.

When were the Hadean and Archean periods?

The Hadean period lasted from the formation of the Earth, about 4.56 billion years ago, to about 4 billion years ago, so its duration is approximately 0.56 billion years. The Archean period lasted from about 4 billion years ago to 2.5 billion years ago, so its duration is approximately 1.5 billion years. The total duration of the Hadean and Archean periods is therefore 0.56 + 1.5 = 2.06 billion years.

Learn more about the combined span of Hadean and Archean here:

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