IN: HOW DO FOSSILS EXPLAIN THE HISTORY OF THE EARTH?

6.5 Time Marches On Pages 151-155

12-16-14

REMEMBER….

Rock layers form oldest on the bottom first, newest on top, so as you go down you go back in time.

HOW DO WE KNOW HOW OLD THE EARTH IS?

Geologic Column is an ideal sequence of rock layers that contain all the known fossils and rock formation on Earth arranged from oldest to youngest.

SCIENTISTS HAVE MEASURED THAT THE EARTH 4.6 BILLION YEARS OLD!

Geologic Time Scale:divides Earth’s 4.6 billionyear history into distinct intervals of time.

HOW IS IT DIVIDED?

Eons are the largest divisions of time. Eons are divided into four eras. Eras are divided into periods. Some periods are divided into epochs.

4.6 billion years ago – 3.8 billion years ago

The only rocks that scientists have found from this eon are meteorites and rocks from the moon.

HADEAN EON

3.8 billion years ago – 2.5 billion years ago

The earliest known rocks on Earth formed during this eon.

ARCHEAN EON

2.5 billion years ago – 540 million years ago

The first organisms with well-developed cells appeared during this eon.

PROTEROZOIC EON

540 million years ago – present The rock and fossil record mainly

represents the Phanerozoic eon. This is the eon in which we live.

PHANEROZOIC EON

The Phanerozoic Eon is divided into three eras and spans 540 mya to present.

THE PALEOZOIC ERA

“Old life” from 540 to 248 mya and the first era that is well represented by fossils.

Beginning with no land organisms ending with as mass extinction of the amphibians and insects that had moved onto the land.

THE MESOZOIC ERA

“Middle-Life” from 248-65 mya, the age of the reptiles.

Dinosaurs dominated the Earth and birds and small mammals began to evolve, ending with 50% of all species becoming extinct.

CENOZOIC ERA

“Recent Life” mya to the present. We live in the Cenozoic era, and other

mammals are abundant. Many mammals that once lived in this

era are now extinct.

CAN YOU IMAGINE 4.6 BILLION YEARS? Humans appearin the last second!

The Colorado River has cut the canyon exposing rock layers that represent nearly 2 billion years of geologic time.

GRAND CANYON

Extends the geologic time scale

Include Zion Canyon and Bryce Canyon

THE GRAND STAIRCASE

OUT: What future event will mark the end of the Cenozoic era?