The Geologic Time ScaleGeologic time is divided into Eons.
1. Precambrian Eon
a) Archean Eon
b) Proterozoic Eon
2. Phanerozoic Eon
The Geologic Time ScaleEons are further divided into Eras.
1. Archean Eon• Eoarchean Era• Paleoarchean Era• Mesoarchean Era• Neoarchean Era
2. Proterozoic Eon• Paleoproterozoic Era• Mesoproterozoic Era• Neoproterozoic Era
3. Phanerozoic Eon• Paleozoic Era• Mesozoic Era• Cenozoic Era
The Geologic Time ScaleThe Phanerozoic Eon is further divided into Periods.
1. Phanerozoic Eon• Paleozoic Era
• Cambrian Period• Ordovician Period• Silurian Period• Devonian Period• Carboniferous Mississippian Period• Carboniferous Pennsylvanian Period• Permian Period
• Mesozoic Era• Triassic Period• Jurassic Period• Cretaceous Period
• Cenozoic Era• Tertiary Period• Quaternary Period
The Geologic Time ScaleThe Cenozoic Era is further divided into Epochs.
• Cenozoic Era• Tertiary Period
• Paleocene Epoch• Eocene Epoch• Oligocene Epoch• Miocene Epoch• Pliocene Epoch
• Quaternary Period• Pleistocene Epoch• Holocene Epoch
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 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
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 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.
The Precambrian Eon
The first primitive prokaryotic single-celled organisms appeared in the
oceans in the form of bacteria
(eubacteria or Achaea).
The earliest life forms were prokaryotes
that evolved in the seas, possibly as early as 3.8 Ga.
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 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 With the eukaryotes comes sexual
reproduction, enabling genetic diversity and the concomitant ability to adapt to and
survive environmental changes.