1. “Nothing hurries geology” - Mark Twain
Geologic Time
“Nothing hurries geology”
- Mark Twain

2. What is Time? Time is how we sense and record
changes in the environment.
It is our sense of one thing happening after another.
We need standards of time for the convenience of everyday life.

3. Units of time
As humans we think of time related to personal experience.
Seconds
Minutes
Hours
Month
Years
Decades
Centuries
Millenia
However, you will see that when we talk
about Earth history, even using a
millennium isn’t sufficient because
of Earth’s vast age.

4. Deep Time When we study history 200, 1,000 or even 2,000 years seems
like a long time.
Geology involves vastly greater
amounts of time
This is referred to as deep time.

5. Geologic Processes Most are slow but relentless
Reflecting the pace at which the heat engines work
It’s unlikely that a mountain will visibly change shape or height during a human lifetime

6. Geologic Processes In a geologic time frame
Most mountains are probably eroding “rapidly”
Uluru is a great block of uptilted sandstone in the heart of Australia's Outback.
This region may be the world's best-developed peneplain,
and Uluru its best-known monadnock.

7. To a geologist . . . “Rapidly” may mean within a few million years.
A “fast” process
Started and completed within a few million years.
For example . . .

8. Rate of Plate Motion At a mid ocean ridge 1 cm/yr movement
100,000 years for the seafloor to move 1,000 km (100,000 cm in one km)

9. Some geologic processes do occur quickly
Mt. St. Helens

10. Landslides Occur Quickly
Tully Valley landslide on April 27, 1993
Occurred after heavy precipitation of
190 mm (7.5 in) during April in conjunction
with melting of a winter snowpack

11. Processes of Change Through time

12. Spatial Scales of Observation
Geologists study all of Earth’s materials from:
The spatial scale of atoms
To the scale of our planet (global scale)

13. Spatial Scales of Observation
Geologists study all of Earth’s materials from:
The spatial scale of atoms

14. Spatial Scales of Observation
Geologists study all of Earth’s materials from:
The spatial scale of atoms

15. Spatial Scales of Observation
Geologists study all of Earth’s materials from:
The spatial scale of atoms
To the scale of our planet (global scale)

16. Global Perspective of Earth

17. Thickness on the model is calculated using a proportion.
119 mm X
6371 km km
(6371 km) X = (119 mm)(16 km)
X = (119 mm)(16 km)
6371 km
X = 0.3 mm
On this scale:
Mt. Everest (8.8 km or 5.5. mi.)
would be 0.16 mm high.
Deepest location in the ocean
(Mariana Trench – 10.9 km or
6.8 mi) would be 0.2 mm deep

18. The Geologic Time Scale
Earth history is subdivided into time units based on:
The fossil record
Extinctions

19. Geologic Time Scale – Temporal Scales of Observation
Like in a book, events and relationships are grouped into
Paragraphs
Sections
Parts
These are the geologic time scale’s
Eons
Eras
Periods
Epochs
The “calendar” into which geologic events are placed.
Phanerozoic

20. Temporal Scales of Observation
Grand Canyon, AZ
Exposed rocks at the bottom of the canyon are more than a billion years old
Sediments in the Colorado River
May have formed just seconds ago

21. Scale Model of Earth History