The Precambrian TimeThe Precambrian Time

Last from 5 billion years ago – 544 million Last from 5 billion years ago – 544 million years agoyears ago

Key Events of Precambrian timeKey Events of Precambrian time

Acasta Gneiss is dated at3.96 bya. It is near Yellowknife Lake , NWT CanadaZircons possibly a bit older in Australia

PrecambriaPrecambriann

• 4.6 billion years to 544 million years.

• Represents 88% of Earth’s history

• 3 divisions• Hadean• Archaen• Proterozoic

EarlyEarly Hadean (hellish) TimeHadean (hellish) Time• 4.6 billion years ago – Earth forms from

“stardust”

• Earth is bombarded by impactors adding to Earth’s mass (adds heat)

• Hot spinning planetary mass caused materials to layer according to density (crust, mantle, core).– Heavy iron and nickel migrate to center (core) – Medium density silicate material moves out to mantle– Lightest float to the crust

•Early earth surface was magma sea, gradually cooled to form the crust.

Hadean Hadean

Formation of ContinentsFormation of Continents

EarlyEarly ArchaeanArchaean• Huge glancing blow from a Mars-sized impactor

created the moon. (Collision Theory)

PrecambrianPrecambrian

Early AtmosphereEarly Atmosphere•1st atmosphere was H + He

•lost to solar wind•Later mostly Nitrogen (inert) and CO2•Liquid water rids CO2 from atmosphere

–Mars is too cold to have liquid water.–Venus is too hot.–Both have CO2 atmospheres.

•On Earth, most of the world’s CO2 is locked up in rock and life!

MarsMars EarthEarthVenusVenus

PrecambrianPrecambrian

Early Oceans about 4 billion Early Oceans about 4 billion years agoyears ago•volcanic stem condenses•Part of the earth’s water probably came from comets

–comets are large dirty snowballs–provide fresh water

•salt in oceans from weathering and carried to the oceans by rivers

–. 3.5 bya - Origin of Life3.5 bya - Origin of Life

OOrigin of Archaebacteriarigin of Archaebacteria• Archaebacteria are the most primitive

fossil life forms –likely ancestors of all life–thermophiles –in deep-sea volcanic vents–feed directly on sulfur

(chemosynthesis)

Why at the vents?Why at the vents?• chemical and heat energy• abundant chemical and mineral compounds, including sulfur

• protection from oxygen and ultraviolet radiation

Fossil Fossil BacteriaBacteria

Move to PhotosynthesisMove to PhotosynthesisBy 2 billion yrs ago CYANOBACTERIACYANOBACTERIA

• Moved from vents to water surface

• Began using sunlight to make food

2 bya Photosynthesis2 bya PhotosynthesisModern Stromatolites Modern Stromatolites Shark Bay AustraliaShark Bay AustraliaUsed to dominate the landscape in Pre-Cambrian and Early Cambrian.

RedbedsRedbeds

2bya - Proterozoic Time:2bya - Proterozoic Time:Oxygen - Rich AtmosphereOxygen - Rich Atmosphere

• Oxygen in atmosphere irradiated - Ozone layer forms, protecting shallow water and land life forms from UV

1.9 bya - Rodinia 1.9 bya - Rodinia

Metamorphic alteration of magnetic minerals makes arrangement uncertain.

Most of North America “Boxed-In”

Note orientation and neighbors of “North America”

N

Snowball Earth Snowball Earth 600 million years ago600 million years ago

• Atmosphere’s CO2 tied up in extensive limestones.

• No greenhouse effect. • Atmosphere can’t trap heat –

gets colder• Oceans froze

•Multi-cellular organisms appear (algae strands, jellyfish, etc.)

•Ediacaran (Vendian) consist of simple flat, platelike organisms.

570-545 million year ago-570-545 million year ago-late Proterozoic Timelate Proterozoic Time

Proterozoic LifeProterozoic Life

Ediacara Fauna

Check yourselfCheck yourself

You may choose more than one letter for some questions! Select ALL that apply for each question.

1. During which Precambrian 1. During which Precambrian division do the oceans form?division do the oceans form?

A.PhanerozoicB.HadeanC.ArchaeanD.Proterozoic

2. What formed the oceans?2. What formed the oceans?

A.Water from the coreB.CometsC.Volcanic vaporsD.Asteroids

3. During which Precambrian 3. During which Precambrian division is Snowball Earth?division is Snowball Earth?

A.PhanerozoicB.HadeanC.ArchaeanD.Proterozoic

4. Put the following events in 4. Put the following events in order as they occurred during order as they occurred during

the Precambrian Eonthe Precambrian EonA. jellyfish & ediacaransB. hydrogen & helium atmosphereC. Single-celled thermophile bacteriaD. cyanobacteriaE. Oceans formF. Oxygen-rich atmosphere

5. What is a major difference between Precambrian

archaebacteria & cyanobacteria?

A. Cyano came firstB. Archae used photosynthesis, while

cyano used chemicals like sulfurC. Cyano lived closer to the ocean’s

surface than the archae didD. Cyano lived along volcanic vents in

the ocean floor and archae lived on land

6 – 10. Explain IN DETAIL how the Precambrian Earth was different than modern day Earth with respect to temperature, biota (life),

atmosphere, age.