Geologic Time
Geologic Time
Chapter 17 section 1
(This is transcribed from a Prentice Hall
read only slide show)
Geologic Time Scale:
|Slide Number |Information |
|761 |To understand Earth, it is important to realize that our planet is very old. |
|762 |Modern methods of radiometric dating put Earth’s age at 4.5 billion years. |
|763 |This immense time span is hard to comprehend. Guess about how long it would |
| |take just to count to 4.5 billion if you could count one number per second |
| |without stopping. 150 years |
|764 |An appreciation for the magnitude of geologic time is important because many of|
| |Earth’s processes are so gradual that vast spans of time are needed for |
| |significant changes to occur. |
|765 |It took millions of years to create these mountains and it will take millions |
| |more to wear them away. |
|766 |Geologists have divided all of Earth history into units of varying magnitude. |
| |Together they comprise the geologic time scale. |
|767 |The time scale provides a framework for arranging events of the geologic past. |
|768 |Eon represents the greatest expanses of time. |
|769 |The eon that began about 540 million years ago is called the Phanerozoic, Greek|
| |for “visible life”. |
|770 |The sedimentary rocks and deposits of Phanerozoic eon contain an abundance of |
| |fossils. |
|771 |The Phanerozoic eon is divided into units called eras. |
|772 |The era names refer to import differences in dominant life-forms. |
| |Paleozoic refers to ancient life. Example Trilobite fossils. |
| |Mesozoic refers to middle life. |
| |Cenozoic refers to recent life. |
|773 |Each era is divided into smaller units called periods. |
|774 |The changing fossil record also played an important part in establishing each |
| |of the periods. |
|775 |Periods may be divided into epochs. Seven epochs are names for the periods of |
| |the Cenozoic era. |
|776 |The epochs of other periods usually are just termed early, middle, and late. |
|777 |The Pleistocene epoch, which ended just 10,000 years ago, coincides with a time|
| |span commonly known as the ice age. |
|778 |The detail on the time scale does not begin until about 540 million years ago, |
| |the date for the start of the Cambrian Period. |
|779 |The vast expanse of time prior to the Cambrian Period is divided into three |
| |eons-the Hadean, the Archean, and the Proterozoic. |
|780[pic] |This greater than 4 billion-year span is also commonly called the Precambrian. |
|781 |About what percent of Earth’s 4.5 billion-year history is represented by |
| |Precambrian time? 88% |
|782 |Why are the eons of Precambrian time not divided into numerous eras and |
| |periods? |
|783 |One reason is that Precambrian life was soft-bodied and therefore the fossil |
| |record is meager compared to the Phanerozoic eon. |
|784 |In addition, much of the Precambrian rock record is buried beneath younger |
| |rocks and/or altered by metamorphism. |
| |The Grand Canyon’s ancient Vishnu schist is buried beneath a huge pile of |
| |Paleozoic rocks. |
|785 |Which is the greatest expanse of time? eon |
|786 |Which is a subdivision of an epoch? None of these |
|787 |Mesozoic is an example of era. |
|788 |Eons are divided into these era. |
|789 |Which is the smallest time span on the geologic time scale? epoch |
|790 |Cambrian and Jurassic are examples of period. |
|791 |The age of the Earth is about: 4.5 billion years |
|792 |The Phanerozoic eon began about years ago. |
| | |
|793 |We are presently living in the Cenozoic era. |
|794 |The Hadean, Archean, and Proterozoic are: eons that collectively comprise the |
| |Precambrian. |
|795 |Which era of the Phanerozoic eon has the most periods? Paleozoic |
| | |
| |Eocene, Pleistocene, and Holocene are examples of: epochs |
|796 | |
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