Chapter 8b – Earth History
Earth’s age is between
4.53 and 4.56 billion years
old. A difficult to fathom
length of time.
To put this in perspective:
Yard is the distance
from King’s nose to his
index finger. If all of
earth’s history is on that
yard stick, then if the
King files his fingernail
once, he just removed all
of human history.
Geologic Time Scale
Geologists and Paleontologists divide relative time into
“zones” that reflect differing earth characteristics.
Eon: Largest interval of geologic time.
Four
Hadean – 4.5 to 4.0 billion years ago
Archean – 4.0 to 2.5 billion years ago
Proterozoic – 2.5 to 0.542 billion years ago
Phanerozoic – 0.542 billion to present
Geologic Time Scale - Eras
The Phanerozoic Eon is divided into three Eras based on
the major life types.
Paleozoic Era – Ancient Life: “Age of
Invertebrates”
Mesozoic Era – Middle Life: “Age of Reptiles and
Dinosaurs”
Cenozoic Era – Recent Life: “Age of Mammals”
Eras are further divided into Periods based
on additional distinctions of life.
Geologic Time Scale - GSA
Geologic Time Scale – Encyclopedia of Life
Let’s divide earth history into a nine volume
encyclopaedia.
Each volume would comprise 500 million years.
Let’s make each volume have 500 pages. Each
page would then represent 1 million years. A very
long time, but very short compared to the age of
earth.
Geologic Time Scale – Volume 1
Volume 1 - 4.5 billion to 4.0 billion
No rocks of these ages present on Earth.
Why?
500 million years of intense meteorite
bombardment.
Plate tectonics.
Erosion of old rocks
Oldest evidence that there were rocks is
4.42 billion years before present. Zircon.
Geologic Time Scale – Volume 1
Evidence of meteorite bombardment.
Age of Earth
determined
from lunar
rocks and
meteorite
radiometric
ages.
Geologic Time Scale – Volume 2
Volume 2 - 4.0 billion to 3.5 billion
No oxygen in atmosphere.
Considerable evidence.
Sedimentary minerals
Volcanic gases
H2O, CO2, SO2, CH4, NH3
Hotter earth because of higher CO2
Sun produces less heat
3.8 billion – earliest evidence of life
Carbon isotope evidence – life is lazy?
Requires self replication – DNA from RNA?
Geologic Time – Hydrothermal Vent
Geologic Time – Tube Worms
Thermophile
bacteria at the
bottom of the
food chain.
Geologic Time Scale – Volume 3
Volume 3 – 3.5 billion to 3.0 billion
Nothing new.
Geologic Time Scale – Volume 4
Volume 4 – 3.0 billion to 2.5 billion
Stromatolite
Geologic Time Scale – Volume 4
Stromatolite
Geologic Time Scale – Volume 4
At 2.5 billion years before present something
really great is about to occur!
Geologic Time Scale – Volume 5
Volume 5 – 2.5 billion to 2.0 billion
Banded Iron Formations are found all over Earth.
First oxygen producing photosynthesis
More efficient!
Oxygen is a deadly poison!
Botulism
Gangrene
How to safely get rid of deadly O2?
Combine it with ferrous iron (Fe2+)
Geologic Time Scale – Banded Iron
Formation
Alternating layers of magnetite iron and red chert.
Geologic Time Scale – Volume 5 continued
Volume 5 – 2.5 billion to 2.0 billion
Major advance in evolution at about 2.2 billion
years ago.
Prokaryote bacteria – reproduces by fission
(asexual reproduction)
Eukaryote bacteria – reproduces by mixing DNA
from two individuals (sexual reproduction).
Advantage: genetic diversity!
Cell nucleus and organelles
Geologic Time Scale – Volume 6
Volume 6 – 2.0 billion to 1.5 billion
Nothing new.
Geologic Time Scale – Volume 7
Volume 7 – 1.5 billion to 1.0 billion
Nothing new.
Geologic Time Scale – Volume 8
Volume 8 – 1.0 billion to 0.54 billion
A great disaster?
Or the best thing to have ever happened?
Photosynthesis is using up CO2 and creating O2 in earth’s
atmosphere.
Global temperatures drop.
Snowball Earth 716 million years before present.
Drop Stone
Paul Hoffman
Snowball Earth
Snowball Earth
Earth is frozen over to the very low latitudes.
What color is earth?
What is earth’s sunlight absorbtion?
0.1 albedo vs. 0.8 albedo for oceans
Will earth ever de-ice? Unlikely. Earth remains frozen.
Except earth is currently not frozen.
What could have happened?
Snowball Earth Thaws Out
Are volcanoes still erupting? What do they erupt?
CO2? Why is CO2 important?
Snowball Earth Environmental Stress
First multi-cellular animal life evolves.
Burrowing organisms.
Change from fissile shales to siltstones that have
no layering.
Snowball Earth Environmental Stress
First multi-cellular life evolves.
Burrowing organisms.
Change from fissile shales to siltstones that have
no layering.
Geologic Time Scale – Volume 9
Volume 9 – 0.54 billion (542 million) to present
Phanerozoic Eon
The “good stuff”
Only 1/9 of earth history (11%)
Abundant life seen as fossils
Geologic Time Scale – Phanerozoic
Volume 9 – 0.54 billion (542 million) to present
Phanerozoic Eon
The “good stuff”
Only 1/9 of earth history (11%)
Abundant life seen as fossils
Divided into three Eras
Geologic Time Scale – Paleozoic
Paleozoic Era
Cambrian Period – first abundant life as seen in
the fossil record.
Hard parts.
Trilobite
Brachiopod
Geologic Time Scale – Paleozoic
Ordovician Period – waterworld (bad movie). Jawless
fish.
Geologic Time Scale – Paleozoic
Silurian Period – Jawed fish.
Geologic Time Scale – Paleozoic
Silurian Period – First land plants.
Falling sealevel
Major development.
Surrounded by nutrients vs.
separate systems above and
below earth’s surface.
Geologic Time Scale – Paleozoic
Devonian Period – Age of Fishes. First tetrapods
(amphibians) from lobe-finned lungfish. First seed plants
(conifers). Insects migrate onto land.
Mississippian – sea-level rises. Amphibians everywhere.
Pennsylvanian – sea-level drops. Amphibians in trouble.
Reptiles evolve amnoionic (hard-shelled) egg. Yippee!
Permian – First mammal-like reptiles.
Greatest extinction of life ever.
80-95% of all species become extinct.
Geologic Time Scale – Mesozoic
Following the extinction of most species of
invertebrates, reptiles become the advanced organisms.
Three periods of the Mesozoic.
Triassic – Pangaea begins to break apart. Species
are isolated and development of new
species occurs.
Reptiles dominate early Triassic. Dinosaurs
evolve towards end of Triassic and dominate
land. Reptiles still dominate the world’s
oceans.
Dinosaur vs. Reptile
Dinosaur
Reptile
Dinosaurs Warm Blooded?
Were dinosaurs warm or cold blooded?
The ratio of oxygen-18 to oxygen-16 can be
used as a thermometer.
Oxygen isotope studies of large (pelvic) vs.
small (finger) bones of cold and warm blooded
organisms indicate:
Some dinosaurs were warm-blooded.
Some dinosaurs were cold-blooded.
Dinosaurs Warm Blooded?
Were dinosaurs warm or cold blooded?
Reptiles are cold blooded.
Birds are warm blooded.
Jurassic
During the Jurassic dinosaurs dominate land.
Jurassic Park dinosaurs are not Jurassic in age. They
are Cretaceous! Why?
Birds evolve from the dinosaurs.
Atlantic Ocean begins to fully form.
First Feathers
Cretaceous
First flowering plants.
Bird and bees proliferate. Why?
One of the strangest means of symbiotic
reproduction.
Cretaceous
Cretaceous mammals are small burrowing organisms.
Cretaceous Mammals
.
Cretaceous-Tertiary Extinction
At the end of the Cretaceous, beginning of the Tertiary
the dinosaurs and many other organisms become extinct.
1. Climate warming and
drying for 10 Mybp.
2. Deccan Traps volcanic
eruption. Adds CO2.
Shiva?
3. Chicxulub Impact.
Cenozoic
There are now new environmental niches for the
mammals to evolve and come to dominate Earth.
The “Age of Mammals”.
Mammals dramatically increase in size since they don’t
have to live in burrows any more.
Some large mammals move back into the oceans.
Whales.
Whales
How do we know they were originally land mammals and
not fish?
Vestigial legs and pelvis.
Linked Horse and Grass Evolution
At the beginning of the Cenozoic horses evolved first in
mid-North America which was heavily forested.
Horse Evolution
Lots of places for horses to hide from predators.
Horse Food
What did early horses eat? We can tell from teeth.
Browsers versus grazers.
Is it easier to eat
grass or leaves?
Horse Food
What did early horses eat? We can tell from teeth.
Browsers versus grazers.
Is it easier to eat
grass or leaves?
You’re right!
It’s easier to eat and
digest leaves than
grass.
Forests Replaced by Grasslands
Over millions of years there are fewer trees and more
grass covered meadows.
Harder for horses to hide from predators. How to
escape?
Run faster? How to accomplish this?
Fewer leaves to eat? Eat grass! How?
Pleistocene Extinction
What happened to these organisms a scant 12,000
years ago?
Humans migrated to North America over the
Bearing Strait. Ate them.
Climate was warming and drying from 21,000 to
18,000 years ago with rapid warming at 12,000
to 11,000 years ago. Environmental stress.
Comet impact? See your handout: “It Came Like
Yesterday”
Extinction
Paleotologists have observed that generally organisms
become larger through time. Why?
Paleotologists have observed that during great
extinctions, it is usually the large organisms that
become extinct. Why?
Humans
Modern humans, as we think of them, have been on
earth for about 5000 years.
What percentage of earth history have humans been
here?
5000
____________
4 500 000 000
=
1
__________
900 000
Early Humans
Neanderthal Child
Very large brains
Red Hair
Neanderthal Range