Geologic TimeGeologic Time
““Nothing hurries geologyNothing hurries geology””
- Mark Twain- Mark Twain
What is Time?What is Time?
• It is our sense of one thing happening after another.
• We need standards of time for the convenience of everyday life.
• Time is how we sense and record changes in the environment.
Units of timeUnits 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.
Deep TimeDeep 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.
Geologic ProcessesGeologic 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
Geologic ProcessesGeologic 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.
To a geologist . . .To a geologist . . .
• “Rapidly” may mean within a few million years.
• A “fast” process– Started and completed within a few million
years.– For example . . .
Rate of Plate MotionRate 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)
Some geologic processes do occur quickly Some geologic processes do occur quickly Mt. St. Helens
Landslides Occur QuicklyLandslides 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
Processes of Change Processes of Change Through timeThrough time
Spatial Scales of ObservationSpatial Scales of Observation
• Geologists study all of Earth’s materials from:– The spatial scale of
atoms– To the scale of our planet
(global scale)
Figure 1-02
Spatial Scales of ObservationSpatial Scales of Observation
• Geologists study all of Earth’s materials from:– The spatial scale of
atoms
Figure 1-02
Spatial Scales of ObservationSpatial Scales of Observation
• Geologists study all of Earth’s materials from:– The spatial scale of
atoms
Figure 1-02
Figure 1-02b
Spatial Scales of ObservationSpatial Scales of Observation
• Geologists study all of Earth’s materials from:– The spatial scale of
atoms– To the scale of our planet
(global scale)
Figure 1-02Figure 1-02t
Global Perspective of EarthGlobal Perspective of Earth
Figure 1-07
Figure 1-18B
• Thickness on the model is calculated using a proportion.
119 mm X
(6371 km) X = (119 mm)(16 km)
X = (119 mm)(16 km)
X = 0.3 mm
6371 km 16 km
6371 km
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
The Geologic Time ScaleThe Geologic Time Scale
• Earth history is subdivided into time units based on:– The fossil record– Extinctions
Geologic Time Scale – Temporal Scales of Geologic Time Scale – Temporal Scales of ObservationObservation
• 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.
Ph
aner
ozo
ic
Temporal Scales of ObservationTemporal 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
Figure 1-01
Scale Model of Earth HistoryScale Model of Earth History