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.

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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