Earth’s History

4.6 Billion years ago Earth was formed

Uniformitarianism

• The theory of Uniformitarianism created by James Hutton as he studied Earth’s history • States:•Earth is an always changing place•The same forces that work today were at work in the past

Earth’s History is divided into sections•Eons The 1st Two Eons are not broken down any further

•Era only the Phanerozoic Eon

• Period • Epoch only the end of the Phanerozoic Eon

•Eons –

• Hadean ~ 4.6 – 3.9 billion years ago• Archeozoic (Archean) ~ 3.9 – 2.5 billion years ago• Proterozoic Eon ~ 2.5 billion years ago to 540 mya• Phanerozoic ~ 540 mya through today

Hadean Eon

• "Rockless Eon" - The solidifying of the Earth's continental and oceanic crusts

• No rocks on the Earth are this old, except for meteorites.

• During Hadean time, the Solar System was forming, probably within a large cloud of gas and dust around the sun

Archeozoic (Archean) Eon

• "Ancient Life" - The first life forms evolve - one celled organisms. Blue-green algae, archaeans, and bacteria appear in the sea

• Atmosphere has a low level of oxygen

Proterozoic Eon

• Broken into 2 periods• No name for the 1st period• First multicellular life: colonial algae and soft-bodied

invertebrates appear• Oxygen build-up in the Mid-Proterozoic.

• 2nd period is Vendian/Ediacaran Period ~ 600 to 540mya

• Vendian biota (Ediacaran fauna) multi-celled animals appear, including sponges• A mass extinction occurred• The continents had merged into a single supercontinent called

Rodinia

Phanerozoic Eon

• This Eon is also know as the Eon of “Visible Life”, we know a lot about the history at this point so it is broken down accordingly

• We will see organisms with skeletons or hard shells

• Time period is 540 MYA through today

Phanerozoic Eon

• Eras• Paleozoic Era ~ 540 to 248 mya• We will see fish and winged insects

• Mesozoic Era ~ 248 to 65 mya• Age of the Reptile• This is when we see the dinosaurs

• Cenozoic Era ~ 65 mya through today• Age of the Mammal

• Eras are broken into Periods• Periods are broken into Epochs

Phanerozoic EonCenozoic EraTertiary PeriodFirst mammalsDeer, pigs, horses, dogsGrass is common

Phanerozoic Eon Cenozoic Era Quaternary Period Pleistocene Epoch

• The first humans (Homo sapiens) evolve• Mammoths, mastodons, saber-toothed cats, giant

ground sloths• A mass extinction of large mammals and many

birds happened about 10,000 years ago, probably caused by the end of the last ice age

Phanerozoic Eon Cenozoic Era Quaternary Period Holocene Epoch

• This is where we are TODAY!!• Human civilization

http://www.timetoast.com/timelines/63215

•How do Scientists find out about Earth’s Past?•What type of Scientist studies Earth’s Past?

Types of Scientists

• Paleontologists study the Earth's past biosphere and current biosphere. Paleontology is the study of prehistoric life, including organisms' evolution and interactions with each other and their environments (their paleoecology)

• An Anthropologist is a scientist who studies prehistoric people and their culture

• An Archeologist is a scientist who studies past human life and culture by the recovery and examination of remaining material evidence, such as graves, buildings, tools, and pottery

• As well as Biologists, Chemists

Fossils

• Traces or remains of living things from long ago• Fossils can give us clues to Earth’s

past• Types of fossils: original remains,

natural evidence, fossils in rocks

Fossils Original remains

• Fossils that are the actual body parts (skin, muscle, bones, hair)• Conditions prevent decomposition• Ice – BEST preserver, large mammoths• Amber – harden resin of trees, insects• Tar- thick, oily liquid, large mammoths

Fossils Original remains Ice- Mammoth found in Siberia

Fossils Original remains Amber – about 40 mya

Fossils Original remains Tar – fossils found in tar pits

Fossils Natural Evidence

• Tree Rings – the width of the rings can give clues to the climate• Wide width = a wet season, good for growth• Thin width = dry season, may give hint to years of

famish• Ice Core – vertical timeline of Earth’s atmosphere

• Air content in different layers gives clues to temperature• Debris can give clues to volcanic eruptions

FossilsNatural Evidence – Tree Ring

FossilsNatural Evidence – Ice Core

Fossils in Rocks

• ONLY in Sedimentary rocks, conditions have to be right• Traces of the hard parts of an organism• 4 types

•Molds and Casts• Petrified Wood• Carbon Films• Trace Fossil

Fossils in Rocks Molds and Casts

• Mold is a visible shape left in sedimentary rock• Over time sediment buries an organism• The soft parts decay first, then the hard parts

decay• Leaving a hollow space to fill with minerals,

which makes a Cast of the organism

Fossils in Rocks Molds and Casts

Fossils in Rocks Petrified Wood

• A fallen tree that has been covered with sediment• Over time minerals replace the wood part of

the tree/ the cells

Fossils in Rocks Carbon Film

• ALL living organisms contain carbon• Sometimes when an organism dies it leaves

behind the carbon – a visible layer• You are able to see the soft parts

Fossils in Rocks Trace fossils

• Evidence of an organism’s presence• Foot prints• Dwellings• Feces

So that brings us back to the question…

How do Scientists KNOW how old the Earth is?

Finding the Age of Rocks

•Relative Age•Rock Layers• Index Fossils

•Absolute Age•Radioactive Dating

Relative Age

•The age of an event or object in relationship to something else

Relative Age

•Sedimentary Rock Layers•Undisturbed layers the youngest layer will

be on the top

Relative Age

• Sedimentary Layers that have been disturbed by folding…follow the layers

Relative Age

• Sedimentary Layers that have been disturbed by igneous rock…the igneous rock will be younger than the rock it goes through, but the sedimentary on top of that will be younger

Relative Age

•Index Fossils – fossils of organisms that lived in many areas and existed ONLY during a specific time

How to use Index Fossils

Absolute Age

• The ACTUAL age of an object or organism• Scientists use a process called Radioactive

Dating – using the half-Life of radioactive elements• Used mostly with igneous rock• This process can NOT be used on

sedimentary rocks (Why?)• Also used for organisms - Carbon

Radioactive Dating

• Everything is made of Atoms• The Atoms of many elements exist in various

forms• Some breakdown, and the way they breakdown is

predictable• The time it takes for half of the atoms in a sample

to change from an unstable form to a new form is called Half-Life

• Each element has its own unique Half-Life

Half-Life

0 Half-Life

1 Half Life

2 Half Lives

3 Half Lives

4 Half Lives

0%10%20%30%40%50%60%70%80%90%

100%

% Chaanged% Original