Time Periods
Period Dates Notable facts
Hadean 4.6Ga - 4Ga This is the first named geologic eon.
The ICS describes the Hadean as “informal”.
The eon is named for Hades the Greek God of the
Underworld, to describe the hellish conditions that were
found on Earth at the time. The planet was very hot due to
its recent accretion and the abundance of many radioactive
elements.
Archean 4Ga – 2.5Ga During Archean, the Earth had cooled enough to for water to
pool on the surface and for continental crust to form,
however the Earth was still many times hotter that it is
today, this was mostly caused by a mix of remanent heat
left over from planetary accretion, the formation of the iron
core and the decay of radioactive materials.
The start and end date for the Archean has been formally
recognised by the ICS.
Archean rocks can be found in Greenland, Siberia, the
Canadian Shield, Montana, Wyoming, the Baltic Shield,
Rhodope Massif, Scotland, India, Brazil, and Western
Australia
The most predominate rock is Granite, usually in the form of
massive melt sheets. There often large plutonic masses of
Granite, diorite, layered intrusions and anorthosites.
The atmosphere lacked any free oxygen, with the sun only
about 70-75% of its current luminosity with most of the
heat on Earth being generated internally.
Evidence of liquid water is provided by clear weathering on
Archean rocks.
Most scientists agree that life first arose on Earth either at
the very end of the Hadean or the Early Archean.
The earliest confirmed fossils are stromatolites which are
microbial mats that form in shallow water. The oldest were
discovered in sandstone in Western Australia and have been
dated to about 3.48Ga
Proterozoic 2.5Ga – 541Mya This eon is defined as the time when oxygen first became
prevalent in the Earth’s atmosphere to just before life began
to diversify and multiply.
There are several well-studied events in this eon.
The hypothesized Snowball Earth.
The evolution of soft-bodied multicellular organisms.
The first advanced single-celled Eukaryotes and multi-
cellular life appears in this time-period.
We also see the first symbiotic relations between
Mitochondria and Chloroplasts develop with their hosts.
Cambrian 541mya – 485.4mya The first global supercontinent Pannotia was breaking up in
the Early part of the Cambrian. Laurentia, Baltica and
Siberia had separated from the main supercontinent to form
isolated land masses. Most of the continental land was in the
Southern Hemisphere however it was drifting North.
Large, high-velocity rotational movement of Gondwana
appears to have occurred during the Early Cambrian.
Period Dates Notable facts
Hadean 4.6Ga - 4Ga This is the first named geologic eon.
The ICS describes the Hadean as “informal”.
The eon is named for Hades the Greek God of the
Underworld, to describe the hellish conditions that were
found on Earth at the time. The planet was very hot due to
its recent accretion and the abundance of many radioactive
elements.
Archean 4Ga – 2.5Ga During Archean, the Earth had cooled enough to for water to
pool on the surface and for continental crust to form,
however the Earth was still many times hotter that it is
today, this was mostly caused by a mix of remanent heat
left over from planetary accretion, the formation of the iron
core and the decay of radioactive materials.
The start and end date for the Archean has been formally
recognised by the ICS.
Archean rocks can be found in Greenland, Siberia, the
Canadian Shield, Montana, Wyoming, the Baltic Shield,
Rhodope Massif, Scotland, India, Brazil, and Western
Australia
The most predominate rock is Granite, usually in the form of
massive melt sheets. There often large plutonic masses of
Granite, diorite, layered intrusions and anorthosites.
The atmosphere lacked any free oxygen, with the sun only
about 70-75% of its current luminosity with most of the
heat on Earth being generated internally.
Evidence of liquid water is provided by clear weathering on
Archean rocks.
Most scientists agree that life first arose on Earth either at
the very end of the Hadean or the Early Archean.
The earliest confirmed fossils are stromatolites which are
microbial mats that form in shallow water. The oldest were
discovered in sandstone in Western Australia and have been
dated to about 3.48Ga
Proterozoic 2.5Ga – 541Mya This eon is defined as the time when oxygen first became
prevalent in the Earth’s atmosphere to just before life began
to diversify and multiply.
There are several well-studied events in this eon.
The hypothesized Snowball Earth.
The evolution of soft-bodied multicellular organisms.
The first advanced single-celled Eukaryotes and multi-
cellular life appears in this time-period.
We also see the first symbiotic relations between
Mitochondria and Chloroplasts develop with their hosts.
Cambrian 541mya – 485.4mya The first global supercontinent Pannotia was breaking up in
the Early part of the Cambrian. Laurentia, Baltica and
Siberia had separated from the main supercontinent to form
isolated land masses. Most of the continental land was in the
Southern Hemisphere however it was drifting North.
Large, high-velocity rotational movement of Gondwana
appears to have occurred during the Early Cambrian.
