Transcript Earth History - Lower Hudson Regional Information Center

Earth History
Precambrian Time
Geologic Time

Geologic time can be measured two
ways:
– Relative Time: Subdivisions of the Earth's
history in a specific order based upon
relative age relationships
– Absolute Time: Numerical ages in "millions
of years" or some other measurement
The Geologic Time Scale
The geologic time scale is based on
relative time, and is ALWAYS written
with the oldest part at the bottom.
 Use your ESRT (pg 8-9) to follow along
with this presentation.
 We will talk about/see a quick review of
all of the life on the Earth during its
earliest history (the Precambrian).

Divisions of Precambrian Time
The Precambrian is the longest division
of Earth’s history (87% of all time).
There are three major subdivisions of
Precambrian time.

– Hadean
– Archaean
– Proterozoic
• Vendian
Hadean Time
(4.5 - 3.8 Billion Years Ago)
 This is the time when the solar system
was forming from a nebula.
– The age of the formation of the solar
system (and earth) come from the ages of
the oldest meteorites.
The earth formed, and was probably a
hot ball of molten rock.
 There are no rocks (and therefore, no
fossils) from Haden Time.

Hadean Time
Asteroid/
Meteorite
Nebula
Archaean Time
(3.8 - 2.5 billion years ago)
The Earth cooled enough so that rocks
could form.
 Earth’s atmosphere was MUCH different
than it is now.

– Little to no O2
– More CO2
The Oldest Fossils

The oldest fossils are approximately 3.7
billion years old.
– The first fossils: Bacteria
– The only fossil found for the first billion
years of biological history on the Earth are
bacteria.

The first bacteria were probably
responsible for creating oxygen in the
atmosphere through photosynthesis.
Bacteria
• Single-celled organisms
• They currently live in
almost every environment
on Earth’s surface today.
Ancient Bacteria
Modern Bacteria
Stromatolites
Mounds of algae and
bacteria with layers
of sediment.
 Still found in some
few areas today’s
oceans

– Shark Bay, Australia.
Proterozoic Time
(2.5 billion to 544 million years ago)

Most fossils from the Proterozoic are
single-celled organisms.
– Prokaryote (no nucleus) and Eucaryote
(with a nucleus) cells.
– Stromatolites are still very common.
In the late Proterozoic (Vendian) some
“soft” organisms began to appear.
Most of these organisms died out at the
end of the Proterozoic.
Proterozoic Fossils
(Vendian Time)
Charnia
Cyclomedusa
Proterozoic Fossils
(Vendian Time)
Dickinsonia
Spriggina
Proterozoic Fossils
(Vendian Time)
End of the Precambrian

The end of the Precambrian is marked
with the extinction of several of the
“strange” animals and the first
appearance of hard shells on Cambrian
animals.