For the exam, you must know all of the information listed on the slides (unless otherwise stated), but not all of the dates. Here are the dates that you

For the exam, you must know all of the information listed on the slides(unless otherwise stated), but not all of the dates. Here are the dates

that you need to know:

4.6 Byr – age of the Earth, beginning of the Hadean Eon3.8 Byr – first possible evidence for bacteria3.5 Byr – stromatolites, first credible evidence of life (bacteria)2.0 Byr – BIFs, presence of oxygen in the atmosphere670 Myr – first evidence of multi-cellular life545 Myr – Precambrian-Cambrian boundary – Explosion of Life245 Myr – The Great Permian-Triassic Extinction (The largest extinction)65 Myr – The KT (Cretaceous-Tertiary) Extinction (Dinosaurs)4 Myr – First hominids

The Geologic Timescale is divided (not evenly) into 4 “Eons”

From oldest to youngest, the Eons are:

Hadean Archaen Proterozoic Phanerozoic

The first 3 Eons are referred to as the Precambrian

Precambrian

The Phanerozoic Eon is the most recent and best understood Eon. It spans from 545 million years to the present day.

The Phanerozoic Eon is divided into 3 time sections called “Eras”.

Paleozoic Era (“old life”) 545-245 million years ago Mesozoic Era (“middle life”) 245-65 million years ago Cenozoic Era (“recent life”) 65 million years ago until now!

The Phanerozoic Eras are subdivided into “Periods.”

The boundaries between periods are determined by distinct changes in the fossil record (for example, an extinction).

The Hadean Eon 4.6 – 3.8 Billion Years ago

The Hadean Eon is the oldest eon, and it lacks a rock record.

The age of the Earth is determined by meteorites to be 4.6 Billion years old. Oldest minerals found on the Earth are 4.1 Billion years old.

It is hypothesized by many geologists that during this Eon, the Earth was extremely hot due to meteorite bombardment.

The surface was covered by an ocean of magma.

There was no liquid water on the surface.

Note: Scientists are not in agreement with what the Earth was like in the Hadean. There are multiple, competing hypotheses.

The Archean Eon 3.8 – 2.5 Billion Years ago

At the beginning of the Archean, the magma ocean cooled enough to form a solid crust on the Earth’s surface. In other words, rocks started to form! Oceans also formed at this time.

The Archean marks the time when the Earth begins recording geologic history in the rock record. It also marks the time when life began.

The first possible evidence of life comes from organic carbon and fossil bacteria in 3.8 Billion year old rocks.



The earliest credible evidence for life comes from 3.5 billion year old stomatolites.

Stromatolites are fossilized mounds of layered bacteria. They still occur today.

The Proterozoic Eon 2.5 Billion Years to 545 million years ago

The Proterozoic Eon marks the time when the Earth cooled enough for plate tectonics to work as it does today.


About 2 Billion years ago, a type of rock called a banded iron formation (BIF) began to appear.

The presence of BIFs indicates that oxygen appeared in the atmosphere, most likely due to photosynthesis of single-celled organisms.

Without oxygen, iron ions exist as Fe2+ that is easily dissolved in water. The early oceans (before 2 Billion years ago) had lots of dissolved Fe2+ in them. Once oxygen appeared in the atmosphere, Fe2+ started to ‘oxidize’, turning into Fe3+. Fe3+ is not soluble in water (cannot be dissolved), so it precipitates and is deposited into layers on the seafloor.

Photosynthesis allows organisms to use sunlight to convert water and carbon dioxide into sugar. A byproduct of that reaction is oxygen. The sugar can then be used for energy.


BIFs have alternating layers of hematite and chert

Hematite

Chert


670 Million years ago - the first evidence for multi-cellular life.

These creatures are called the Ediacaran fauna

They were soft-shelled animals similar to jellyfish or worms (no shells)

The Phanerozoic Eon 545 million years ago until today

Paleozoic Era (545-245 million years ago)

545 million years ago (at the Precambrian-Cambrian boundary), an abundant amount of hard-shelled, multi-cellular organisms appear in the fossil record. This is often referred to as “The Explosion of Life.”The diversity of fossils dramatically increased.

During much of the Paleozoic, shallow seas covered parts of the continents, providing a rich environment for sea plants and animals.


Cambrian Period (545-510 million years ago)

Trilobites, Brachiopods, and Molluscs (snails, clams, and squids) appear in the fossil record.

Trilobites make up 50% of all species.

trilobitebrachiopod

mollusc


Ordovician Period (510-440 million years ago)

Armored fishes, corals, and graptolites (floating colonies of organisms) appear in the fossil record.

armored fish

coral

graptolite


Silurian Period (440-408 million years ago)

Coral reefs develop.First land plants (Before this time the continents were barren)


Devonian Period (408-360 million years ago)

Also called ‘the age of fishes.’ Fish species become diverse.Land becomes forested.First land animals (Insects and amphibians).


Carboniferous Period (360-286 million years ago)You don’t need to know this, but the Carboniferous is often called the Mississippian and Pennsylvanian Periods instead.

Many swamps existed in North America and Europe (forming much of the coal that we mine today).

Appalachian mountains begin to form. Very large mountain range!

First reptiles (can lay eggs on land, unlike amphibians)

http://upload.wikimedia.org/wikipedia/commons/8/83/Tortoise-Hatchling.jpg


Permian Period (286-245 million years ago)

Dimetrodons (sail backed reptiles) and Therapsids (mammal-like reptiles) are first observed in the fossil record.

The supercontinent Pangea has formed, drastically changing the environment. The internal parts of Pangea have a harsh, dry climate.

dimetrodon

therapsid

The Great Permian-Triassic Extinction (245 Million years ago)

90-95% of all species disappeared from the fossil record!

This is the greatest extinction known; much larger than that associated with the death of the dinosaurs (which occurs later).

Geologists are unsure of what caused this extinction, but it is thought to have been caused by either:

Formation of Pangea Reduced continental shelf (shallow sea regions off the coast) Large landmass leads to harsh climates in interior regions

Massive flood basalt volcanism that occurred in Siberia

A meteorite impact?

Mesozoic Era (245-65 million years ago) – Age of the Dinosaurs

Triassic Period (245-208 million years ago)

Dinosaurs first appear

First mammals – small and probably nocturnal


Jurassic Period (208-144 million years ago)

Stegosaurus and Sauropods appear

The first feathered bird-like reptile Archaeopteryx appears (perhaps the ancestor of birds!)


Cretaceous Period (144-65 million years ago)

Tyrannosaurus Rex and Triceratops appear

The first flowering plants appear The Rocky Mountains start to form

The Cretaceous-Tertiary Extinction(also called the K-T Extinction)

Dinosaurs, and most plankton and plant species became extinct

In recent years, there has been an abundance of evidence supporting the hypothesis that a large asteroid caused this extinction.

An impact site of the same age as the extinction was found on the Yucatan Peninsula in Mexico. This is called the Chicxulub crator.

Geophysical evidence of impact crater

Cenozoic Era (65 million years ago until today) – Age of the Mammals

Tertiary and Quaternary Periods

Some reptiles survived the K-T extinction (crocodiles, alligators, turtles, and lizards).

Mammals rapidly diversifyIncrease in sizeIncrease in brain capacitySpecialization of teeth and limbs

Birds rapidly diversify

Grasses become widespread plants, and large grazing mammals appear

First Hominids (4 million years ago)

For the exam, you must know all of the information listed on the slides(unless otherwise stated), but not all of the dates. Here are the dates

that you need to know:

4.6 Byr – age of the Earth, beginning of the Hadean Eon3.8 Byr – first possible evidence for bacteria3.5 Byr – stromatolites, first credible evidence of life (bacteria)2.0 Byr – BIFs, presence of oxygen in the atmosphere670 Myr – first evidence of multi-cellular life545 Myr – Precambrian-Cambrian boundary – Explosion of Life245 Myr – The Great Permian-Triassic Extinction (The largest extinction)65 Myr – The KT (Cretaceous-Tertiary) Extinction (Dinosaurs)4 Myr – First hominids

Documents

For the exam, you must know all of the information listed on the slides (unless otherwise stated), but not all of the dates. Here are the dates that you