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

Eon Longest time unit measured in billions of year. The Archean, Proterozoic, and Phanerozoic are eons.

Era Measured in hundreds of millions to billions. Defined by the differences in Life- forms found in rocks.

Period Measured 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

Epoch Measured 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 s 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