Geologic History

Historical Geology studies the origin of

Earth and the development of the

planet through its 4.6- billion-year history.

Historical geology investigates the

sequence of events that have occurred

in the past.

Paleontology - the study of fossils

(living organisms, animals and plants

that once existed on the plant).

Geologic time• Thinking in terms of “millions of years”

• Try it in seconds, just for fun: 1,000,000 seconds

How many minutes is this? 1,000,000 seconds / 60 seconds per minute This = 16,667 minutes

How many hours is this? 16,667 / 60 minutes per hour = 278 hours

How many days? 278 hours / 24 hours per day = 11.6 days

• So, 1 million seconds ~ 12 days

How does 1 million compare to 1 billion?

• Again, in seconds just for fun: 1,000,000,000 seconds

How many minutes is this? 1,000,000,000 seconds / 60 seconds per minute This = 16,666,667 minutes

How many hours is this? 16,666,667 / 60 minutes per hour = 277,778

hours How many days?

277,778 hours / 24 hours per day = 11,574 days

Keep going…

• 11,574 days--how many weeks is this?

• 11,574 / 7 days per week = 1,653 weeks Great, now how many years is this?

• 1,653 weeks / 52 weeks per year

• This equals 32 years

• So, one billion seconds = 32 years

• And one million seconds = 11 days

• Now instead of seconds, lets think in YEARS

Understanding the evolution of Earth

requires an appreciation of the immensity of

geologic time

Geologic time

Time is the main aspect of Geology

Geologic time

To understand geologic time, do not think in terms

of seconds, minutes, hours days and years (human perspective)

Geologic time

To understand geologic time you

must think in millions of years.

Geologic time

Example:

Himalayas start to develop 50 mya. It is difficult to say that Himalayas formed 50,000,000 years ago or

18,250,000,000 days ago.

Geologic time

Geologic Time

• The time divisions are:

Eon

Era

Period

and

Epoch

EonLongest time unit

measured in billions of year. The Archean,

Proterozoic, and Phanerozoic are eons.

EraMeasured in hundreds of millions to billions.

Defined by the differences in Life-

forms found in rocks.

PeriodMeasured in terms

of tens of millions to hundreds of millions

of years.

Period Defined by the life-

forms that were abundant or became

extinct during the time in which specific rocks

were deposited

EpochMeasured in millions to tens of millions of

years. Defined by different

groups of organisms.

Regardless of how a geologic time division was defined, each unit

contains specific characteristics that set it

apart from the rest of geologic history.

“The Present is the Key to the Past”

Geologic Time

Earth Development

Catastrophism - everything

happened at once

Hypotheses for Earth Development: Catastrophism

• 1600-1700s

• Landscape formed through a series of catastrophes Mountains, canyons formed during sudden

world-wide disasters triggered by unknowable causes that no longer operate

Uniformitarianism - the processes occurring today

have been occurring since Earth formed.

Uniformitarianism means:• Geological processes operate over

extremely long periods of time• Catastrophic events are included as

punctuated events• Rates and intensities vary but physical and

chemical laws have remained the same• Example: erosion