Part VI. Dating, Interpreting Geologic Histories, and Geologic Time.

4. The vastness of geologic time. The Earth is 4.5 billion years old and records a long history of evolution of the oceans, atmosphere, and life.

Here is a podcast series from the Open University in the U.K. that illustrates the vastness of geologic time. Check out the one called "The age of rocks".

This diagram shows some of the major events in Earth history. <--- Click on this image to see a bigger version.

5. How is Time Recorded in Sedimentary Rocks?

<--- Click on this image to see a bigger version.

Be sure to learn about gaps in the sedimentary record: Unconformities (know the 3 types, see section 10.4 in textbook).

6.) Gaps in the Sedimentary rock record = Unconformities = “missing time”

a.) Types:

i.) A boundary that represents a major time break between flat-lying sedimentary layers: Disconformity.

ii.) A boundary between tilted sedimentary layers below + flat- lying ones above: Angular Unconformity.

iii. Contact between crystalline rocks (igneous or metamorphic rocks, ex. granite, schist, gneiss, diorite) below and overlying sedimentary layers = Nonconformity.

• The time is takes for the Earth to orbit the sun = 365.242199… days
• = 364 days, 5 hrs, 48 minutes, 45.9678… seconds

What is a Month =?

• The time it takes for the moon to orbit the Earth = 29.53059 days
• The Hebrew and Islamic calendars are based on lunar months that = 30 days, so that more than half a day (0.53059 day) per month really adds up and means that holidays shift around a lot.

Julian Calendar = 365.25 days +

• Adds leap year- add a day every 4 years
• Is greater than an actual year by 11 minutes.

Gregorian Calendar (what we use)

• Gregorian Year = 25.96 seconds greater than an actual year -- pretty close.

Back to the beginning of relative dating, geologic histories, and geologic time.