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EARLY EARTH
• The Precambrian is a time period that include
90% of Earth’s history
• Including Hadean, Archean, and Proterozoic
Eons
• Absolute age dating has revealed that
– Old crustal rocks are between 3.96 and 3.8 billion
years in age
– Earth is older than 3.96 billion years old because
of Zircon
What is Zircon
• Zircon is a mineral found in metamorphosed
Precambrian rocks in Australia.
• Can survive erosion and metamorphism
• Often used to age-date old rocks
Solar System Evidence
• Evidence from meteorites and other bodies in
the solar system suggest Earth is more than
4.4 billion years old.
• Scientists agree that everything in the solar
system (Planets, Meteorites, Satellites, and
Rocks) formed at the same time.
Earth’s Early Heat Sources
• 3 likely sources of heat
Gravitational Contraction
• Earth formed by an accumulation of small
rocky bodies around the sun. Overtime they
grew in size. As they grew so did the increase
in gravity, causing the internal temperature
rise with the pressure
Radioactivity
• Because the amount of uranium and other
radioactive isotopes were so abundant in early
Earth, caused more heat to be generated
Asteroid and Meteorite Bombardment
• Today most asteroids orbit Mars and Jupiter.
• Evidence from the surface of the moon and
other planets suggest that for the first 500 to
700 million years asteroids were throughout
the solar system.
• As asteroids impacted the earth they
generated a great amount of heat.
Cooling
• With the effects of heat, eventually Earth
cooled enough for an atmosphere and ocean
to form.
• It’s unknown how long it took for the cooling
to happen
• It’s estimated water formed within Earth’s 200
million years.