1. Ch.3, Sec.5 – Time Marches On Geologic Time
- Earth is 4.54 billion years old or 4,540 million years old!
- our solar system is 4.6 billion years old & the Universe is billion years old!
- we can observe almost 2 billion years of earth’s history in the rock layers in the Grand Canyon

2. Ch.3, Sec.5 – Time Marches On The Geologic Time Scale
- geologists created the geologic time scale as a way to divide Earth’s 4.5 billion year history into distinct intervals
- the largest divisions of time are called eons & there are 4 of them
- the second largest division of time is called an era there are 3 of them

3. Ch.3, Sec.5 – Time Marches On
- the third largest division of time is called a period & there are 13 of them
- the smallest division of time is called an epoch & there are 7 of them
- species of creatures have increased or decreased dramatically during Earth’s history

4. Ch.3, Sec.5 – Time Marches On

5. Ch.3, Sec.5 – Time Marches On
- many species have suffered extinctions, or the death of every member, from climate changes, changes in ocean currents, and asteroids

6. Ch.3, Sec.5 – Time Marches On The Paleozoic Era – Old Life
- the first well represented era by fossils was the Paleozoic Era, which lasted from 543 mya to 248 mya
- most of the species were aquatic in the early stages, but reptiles, amphibians, and plants began to flourish by the end of the era
- scientists believe ocean changes caused the largest mass extinction in Earth’s history around 248 mya

7. The Paleozoic Era – Old Life
Ch.3, Sec.5 – Time Marches On
The Paleozoic Era – Old Life

8. Ch.3, Sec.5 – Time Marches On The Mesozoic Era – The Age of Reptiles
- the age of the reptiles began about 248 mya & ended around 65 mya
- dinosaurs, mammals, and birds began to show up on the planet during this era
- 15 to 20% of all species, including the dinosaurs, went extinct at the end of the era from climate change caused by an asteroid

9. The Mesozoic Era – The Age of Reptiles
Ch.3, Sec.5 – Time Marches On
The Mesozoic Era – The Age of Reptiles

10. Ch.3, Sec.5 – Time Marches On The Cenozoic Era – The Age of Mammals
- the age of the mammals began about 65 mya & is still going strong
- mammals were more adapted for climate change than the dinosaurs, so they flourished after the dinosaurs went extinct

11. The Cenozoic Era – The Age of Mammals
Ch.3, Sec.5 – Time Marches On
The Cenozoic Era – The Age of Mammals