Warm-up:

• Set-up a new page of Cornell Notes: The Precambrian Eon, then:

• Draw a picture of the Earth’s Layers and label the inner core, the outer core, the crust, and the mantle.

Early Evolution of EarthFormation of Earth’s Layered

Structure o As Earth formed, the decay of

radioactive elements and heat from high-velocity impacts caused the temperature to increase.

o Iron and nickel began to melt and sink toward the center

o Lighter rocky components floated outward, toward the surface

o Gaseous material escaped from Earth’s interior to produce the primitive atmosphere

The Atmosphere

• What are the Jovian planets mostly made of?

• The Earth’s atmosphere started out the same – but it didn’t last.

• So where did the air we have now come from?

The Atmosphere

• VOLCANOES and COMET IMPACTS• Volcanoes released carbon dioxide, methane

and water vapor trapped in the mantle• The rest of the water came from comets

The Atmosphere

• As the atmosphere cooled, the water vapor rained out and formed the oceans.

• Where did all the oxygen come from?

The Precambrian Eon It was during the Precambrian Eon

that life first began on the

Earth.Although the

Precambrian Eon contains some 88%

of Earth's history, its fossil record is poor because organism were soft-bodied during this time, resulting in little

remaining evidence.

The Precambrian Eon The earliest life

forms were prokaryotes

that evolved in the seas, possibly as early as 3.8 Ga.The first primitive

prokaryotic single-celled organisms appeared in the

oceans in the form of bacteria

(eubacteria or Achaea).

The Precambrian Eon Earth’s first living organisms were probably

chemotrophs existing in an anoxic world and producing H2S or CO2.

The Precambrian Eon Nearly 3.5 Ga, photosynthezing

cyanobacteria began releasing oxygen into the atmosphere as a by-product of the

process of photosynthesis.

The Precambrian Eon The majority of Precambrian fossils are stromatolites that

are often heavily metamorphosed or deeply

buried.However, preserved cells have been discovered at selective sites, such as the 2.0 Ba Gunflint Formation Jasper stromatolites

from Gunflint Formation near Mackies, northern Ontario.

Modern Stromatolites

• http://www.sharkbay.org/default.aspx?WebPageID=129

• http://www.sharkbay.org/Assets/Multimedia/Test/Stromatolite.swf

The Precambrian Eon The first multi-cellular organisms appeared

toward the end of the Precambrian Eon, sometime prior to 542 Ma.

The Precambrian Eon When the eukaryotes (single-celled

organisms with a nucleus) evolved through endosymbiosis is disputed, with claims as

early as 3.4 Ga, but with less equivocal fossils dating from 1.8 to .8 Ga.

The Precambrian Eon The Precambrian

Eon, which is divided into the Archean and the Proterozoic Eons, spans about 88% of

Earth’s history. Much of Earth’s stable continental crust was created during this time.Partial melting of

the mantle formed volcanic island arcs and ocean

plateaus.

The Precambrian Eon These crustal

fragments collided and accreted to

form larger crustal provinces.

Larger crustal areas were

assembled into larger blocks

called cratons.Cratons form the core of modern

continents.

Formation of Continental Crust

According to one model, the growth of large continental masses were accomplished through the collision and

accretion of various types of terrains, including volcanic arcs and oceanic plateaus.

The Extent of Crustal Materials Remaining From the Archean and Proterozoic Eons

Map showing the major geological provinces of North America and their ages in billions of years

(Ga). It appears that North America was

assembled from crustal blocks that were joined

by processes very similar to modern plate

tectonics. These ancient collisions produced

mountainous belts that include remnant island

arcs trapped by colliding continental fragments.

The Precambrian Eon The

Supercontinents The supercontinents

were large landmasses that consisted of all, or

nearly all, of the existing continents.

Pangaea was the most recent supercontinent, but perhaps an even larger one, Rodinia,

preceded it.Splitting and

reassembling of supercontinents have

generated most of Earth’s major mountain

belts.Supercontinents have

also profoundly affected Earth’s climate over

time.

Possible configuration

of the supercontinent

Rodinia

Figure 12.15