Layers of the Earth
18.1
The Geologic Time Scale
The Geologic column –
represents a timeline of Earth’s
history, with the oldest fossils at
the bottom.
Geologic Column
See Text p. 375 (Great uncomformity)
The Construction of the Geologic Column
No single area on earth contains
a record of all geologic time, so
scientists combine their
observations from around the
world to create a standard
arrangement of rock layers.
What do we call
the line between
layers B and C?
The Geologic Column is based on hundreds of
years of scientific research from all over the world.
• Divided by major changes in climate, or the
extinction of a large group of organisms.
Period – characterized by specific fossils
Named for the location in which the rocks
containing the identifying fossils were first found.
Epoch – subdivision of Cenozoic ONLY!
Cenozoic has an abundance of extremely
detailed fossil record. Only in the Cenozoic are Periods divided into Epochs.
We live in the Cenozoic Era,
the Quaternary Period,
and Holocene Epoch !
Divisions of Geologic Time
Extinction of species is predicted by evolution.
18.2 Geologic History
Theory of Evolution
Organisms change over time, and
new kinds of organisms are derived
from ancestral types.
1.
2.
3.
4.
Proposed by Charles Darwin in 1859
Individual in a population vary in each generation
Some of these variations are genetic, or inherited
More individuals are produced than live to grow up and reproduce
Individuals with some genes are more likely to survive and reproduce
than others.
The fossil record is more evidence for evolution. Many organisms do not survive.
If fact, 99% of all organisms that have ever lived are now extinct.
How species evolve
18.2
Geologic History
Era – largest unit of geologic time
1. Precambrian time
• oldest layers of the geologic column
• lasted much longer than other eras
• very few fossils have been found
o early Precambrian, bacteria & algae
o late Precambrian, primitive worms,
sponges, and coral
Evidence that life began in the ocean
2. Paleozoic Era – Meaning “ancient life”
From 325 – 180 million years ago
Wide variety of fossils, both marine and land
plants and animals
Periods:
Permian – Pangaea comes together; 95% mass extinctions
Carboniferous – Amphibians flourish, sea stars common; forests & swamps; giant insects
Devonian – Age of fishes; 1st amphibians; ferns & cone-bearing plants develop
Silurian – 1st Echinoderms; eurypterids (sea scorpions); 1st land plants and animals appear
Ordovician – Trilobites decline; 1st vertebrates appear (fishes)
Cambrian – Trilobites & brachiopods common
Brachiopods
Trilobite
Earliest fish: ostracoderms
Eurypterids
Horsetails
3. Mesozoic era – Meaning “middle life”
From 180 – 65 million years ago
More-complex fossils like reptiles
and birds
Periods:
Cretaceous – 1st flowering plants; mass extinction of all non-avian dinosaurs
(~ 75% of species mass extinction)
Jurassic – Dinosaurs dominant; flying reptiles & first birds
Triassic – Ammonites common; cycads & conifers; first mammals appear
4. Cenozoic – Meaning “recent life”
From 65 million ago
Fossils of mammals common
Periods:
Quaternary –
Holocene: End of last ice age; complex human societies
Pleistocene: Woolly mammoths, rhinos, and early humans
Tertiary –
Pliocene: large carnivores (bears, dogs, cats)
Miocene: Grazing herds abundant; raccoons, wolves
Oligocene: deer, pigs, horses, a, cats, and dogs
Eocene: horses, flying squirrels, bats, whales
Paleocene: Age of mammals begins; lemuroids
Timeline compressed to 1 Year
Jan 1 – Earth is formed
Feb 25 – First cells
July 17 – First cells with nuclei
Nov 18 – First animals evolve
Dec 1 – First tetrapods (4 legs)
Dec 14 – First mammals
Dec 26 – Mass extinction of the dinosaurs
Dec 31 – Humans first appear at 11:35 pm
Dec 31 – Humans build Stonehenge about 11:59:30
http://www.slate.com/blogs/bad_astronomy/2012/12/31/history_of_earth_video_of_earth_s_timeline_compressed_into_one_minute.html
Earth time Music video
Geologic Time Music Video- BlethwynFilms (by “The Script”)
http://www.youtube.com/watch?v=7PQURsc2SYs
Words to song above
http://www.youtube.com/watch?v=FXpeovWDi9k
National Geographic: The Story of Earth HD (1:30:01)
http://www.youtube.com/watch?v=Xsn3wpVAcjk
Timeline Pictures
Early fishes
bacteria
crinoids
brachiopods
cyanobacteria
early life
Early echinoderms
eurypterids
trilobites
echinoderms
Paleozoic