6.5 Time Marches On Pages
Rock layers form oldest on the bottom first, newest on top, so as you go down you go back in time.
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.
Geologic Time Scale: divides Earth’s 4.6 billion year history into distinct intervals of time.
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.
3.8 billion years ago – 2.5 billion years ago The earliest known rocks on Earth formed during this eon.
2.5 billion years ago – 540 million years ago The first organisms with well-developed cells appeared during this eon.
540 million years ago – present The rock and fossil record mainly represents the Phanerozoic eon. This is the eon in which we live.
The Phanerozoic Eon is divided into three eras and spans 540 mya to present.
“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.
“Middle-Life” from 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.
“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.
Humans appear in the last second!
The Colorado River has cut the canyon exposing rock layers that represent nearly 2 billion years of geologic time.
Extends the geologic time scale Include Zion Canyon and Bryce Canyon
OUT: What future event will mark the end of the Cenozoic era?