Geologic Time Scale

What are your observations?

What can the Grand Canyon tell us about the Earth’s History?

Geologic Time Scale Geologic Time Scale is a record of Earth’s history from its origin 4.6 billion years ago to present.

older younger Oldest time is at the bottom As you move upward each division is younger

Think about it… Would you explain to someone how far away Sonic is from school? Would you explain how far away summer break is by using seconds?

Periods of time You would use miles to explain how far Sonic is from school. You would use weeks or months to explain how far summer break is from today. We do the same thing when we measure Earth’s history. We use different units to measure different periods of time.

Periods of Time What would you do if you had to come up with names for long periods of time (millions or billions of years)?

Geologic Time Eon- The longest time unit: measured in billions of years Ex) Proterozoic, Phanerozoic

Eras Era- The next longest span of time: measured from hundreds of millions to billions of years. Eras are defined by different life forms found in the rocks.

Names of eras are based on relative age Paleo = old meso= middle Ceno= recent zoic= of life See Page 231

Literally what does Paleozoic Era mean? Old Life

Even though its only represented by a small part of this scale, Precambrian time makes up 90% of geologic time During the Paleozoic era the oceans became full of diverse plants and animals! During the Mesozoic Era dinosaurs ruled the land!

If we puts Earth’s history into a year, it would look like this… Precambrian from January 1 – November 17 (10 months) Paleozoic from November 18-December 12 (< 1 month) Mesozoic from December 13 – December 26 (<2 weeks) Cenozoic from December 27 – January 1 (< 1 week)

Geologic Time Periods- the third longest span of time: measured in tens of millions to hundreds of millions of years. Defined by the life forms that were abundant or became extinct during that time Some are named for geographic regions Ex) Mississippian, Pennsylvanian

Geologic Time Epochs- The smallest division of geologic time: measured in millions to tens of million years. Different groups of organisms are used to distinguish the various epochs.