Chapter 8b – Earth HistoryChapter 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, thenif the King files his fingernail once, he just removed all of human history.

Geologic Time ScaleGeologic 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 agoArchean – 4.0 to 2.5 billion years agoProterozoic – 2.5 to 0.542 billion years

agoPhanerozoic – 0.542 billion to present

Geologic Time Scale - ErasGeologic 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 - GSAGeologic Time Scale - GSA

Geologic Time Scale – Encyclopedia of Geologic Time Scale – Encyclopedia of LifeLife

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 1Geologic 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 rocksOldest evidence that there were rocks

is 4.42 billion years before present. Zircon.

Geologic Time Scale – Volume 1Geologic Time Scale – Volume 1

Evidence of meteorite bombardment.

Age of Earth determined from lunar rocks and meteorite radiometric ages.

Geologic Time Scale – Volume 2Geologic Time Scale – Volume 2

Volume 2 - 4.0 billion to 3.5 billion

No oxygen in atmosphere.Considerable evidence.

Sedimentary mineralsVolcanic 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 VentGeologic Time – Hydrothermal Vent

Geologic Time – Tube WormsGeologic Time – Tube Worms

Thermophile bacteria at the bottom of the food chain.

Geologic Time Scale – Volume 3 Geologic Time Scale – Volume 3

Volume 3 – 3.5 billion to 3.0 billion

Nothing new.

Geologic Time Scale – Volume 4 Geologic Time Scale – Volume 4

Volume 4 – 3.0 billion to 2.5 billion

Stromatolite

Geologic Time Scale – Volume 4 Geologic Time Scale – Volume 4

Stromatolite

Geologic Time Scale – Volume 4 Geologic Time Scale – Volume 4

At 2.5 billion years before present something really great is about to occur!

Geologic Time Scale – Volume 5 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 photosynthesisMore efficient!Oxygen is a deadly poison!

BotulismGangrene

How to safely get rid of deadly O2?Combine it with ferrous iron

(Fe2+)

Geologic Time Scale – Banded Iron Geologic Time Scale – Banded Iron FormationFormation

Alternating layers of magnetite iron and red chert.

Geologic Time Scale – Volume 5 Geologic Time Scale – Volume 5 continued 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!

Geologic Time Scale – Volume 6Geologic Time Scale – Volume 6

Volume 6 – 2.0 billion to 1.5 billion

Nothing new.

Geologic Time Scale – Volume 7Geologic Time Scale – Volume 7

Volume 7 – 1.5 billion to 1.0 billion

Nothing new.

Geologic Time Scale – Volume 8Geologic 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.

Temperatures drop.

Snowball Earth 716 million years before present.

Drop StoneDrop Stone

Snowball EarthSnowball Earth

Snowball EarthSnowball Earth

Earth is frozen over to the very low latitudes.

What color is earth?

What is earth’s reflectivity?0.1 albedo vs. 0.8 albedo for oceans

Will earth ever de-ice? Unlikely.

Except earth is currently not frozen.

What could have happened?

Snowball Earth Thaws OutSnowball Earth Thaws Out

Are volcanoes still erupting? What do they erupt?

CO2? Why is CO2 important?

Snowball Earth Environmental StressSnowball Earth Environmental Stress

First multi-cellular life evolves.

Burrowing organisms.

Change from fissile shales to siltstones that have no layering.

Snowball Earth Environmental StressSnowball Earth Environmental Stress

First multi-cellular life evolves.

Burrowing organisms.

Change from fissile shales to siltstones that have no layering.

Geologic Time Scale – Volume 9Geologic 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 – PhanerozoicGeologic 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 – PaleozoicGeologic Time Scale – Paleozoic

Paleozoic Era

Cambrian Period – first abundant life as seen in the fossil record.

Hard parts.Trilobite Brachiopod

Geologic Time Scale – PaleozoicGeologic Time Scale – Paleozoic

Ordovician Period – waterworld (bad movie). Jawless fish.

Geologic Time Scale – PaleozoicGeologic Time Scale – Paleozoic

Silurian Period – Jawed fish.

Geologic Time Scale – PaleozoicGeologic Time Scale – Paleozoic

Silurian Period – First land plants.

Falling sealevel

Major development.Surrounded by nutrients vs.

Separate systems above andbelow earth.

Geologic Time Scale – PaleozoicGeologic 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 – MesozoicGeologic 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. ReptileDinosaur vs. Reptile

Dinosaur Reptile

Dinosaurs Warm Blooded?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?Dinosaurs Warm Blooded?

Were dinosaurs warm or cold blooded?

Reptiles are cold blooded.Birds are warm blooded.

JurassicJurassic

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 FeathersFirst Feathers

CretaceousCretaceous

First flowering plants.Bird and bees proliferate. Why?One of the strangest means of symbiotic

reproduction.

CretaceousCretaceous

Cretaceous mammals are small burrowing organisms.

Cretaceous MammalsCretaceous Mammals

.

Cretaceous-Tertiary ExtinctionCretaceous-Tertiary Extinction

At the end of the Cretaceous, beginning of the Tertiary the dinosaurs and many other organisms become extinct.

1. Climate warming anddrying for 10 Mybp.

2. Deccan Traps volcaniceruption. Adds CO2. Shiva?

3. Chicxulub Impact.

CenozoicCenozoic

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.

WhalesWhales

How do we know they were originally land mammals and not fish?

Vestigial legs and pelvis.

Linked Horse and Grass EvolutionLinked Horse and Grass Evolution

At the beginning of the Cenozoic horses evolved first in mid-North America which was heavily forested.

Horse EvolutionHorse Evolution

Lots of places for horses to hide from predators.

Horse FoodHorse Food

What did early horses eat? We can tell from teeth. Browsers versus grazers.

Is it easier to eat grass or leaves?

Horse FoodHorse 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 GrasslandsForests 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 ExtinctionPleistocene 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”

ExtinctionExtinction

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?

HumansHumans

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 1____________ = __________ 4 500 000 000 900 000

Early HumansEarly Humans

Neanderthal Child Red Hair Very large brains

Neanderthal RangeNeanderthal Range