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Transcript
Methods for Estimating the Age of the Earth
Fossils and evolution
Rates of deposition of sediments
Cooling of the Earth from a molten state
Radiometric Dating
Half-Lives of Radioactive Isotpes
Examples of Very Old Rocks Found on Earth:
3.4 billion year old granites - South Africa.
3.7 billion year old granites - Greenland.
Oldest terrestrial rocks > 3.8 billion years.
Oldest terrestrial rocks (4.0 billion years?) are deep in
the interiors of continents.
Oldest terrestrial rocks (4.0 billion years?) are deep in
the interiors of continents.
But, rocks on the Earth have been weathered,
metamorphosed and recycled through a very
dynamic planet.
Thus, the Earth's earliest rocks have been
recycled, and we need to look beyond Earth to
find evidence of when the Earth solidified.
Rock
Cycle
Mountain
Building
and
Erosion
Oldest terrestrial rocks (4.0 billion years?) are deep in
the interiors of continents.
Similar Rock Structures
Reconstruction of Pangaea
But, rocks on the Earth have been weathered,
metamorphosed and recycled through a very
dynamic planet.
Thus, the Earth's earliest rocks have been
recycled, and we need to look beyond Earth to
find evidence of when the Earth solidified.
Solar System
Meteorites
Meteorites are the remains of rocky and metallic
material that fall to the earth from inter-planetary
space.
These meteorites are thought to be representative
samples of material that formed the early solar
system, and they are believed to have solidified at
about the same time as the earth.
Meteorites
Meteor Crater, Arizona (about 0.75 miles across
and about 560 feet deep). The crater was created
approximately 50,000 years ago.
Major Impact Structures
200-million-year-old
eroded impact
structure in Quebec,
Canada
(42 miles across)
Radiometric Dating of Meteorites
Meteorites have been found to be about 4.4 to 4.6
billion years old.
Since these meteorites are thought to be
representative samples of material that formed the
early solar system, the earth is now believed to be
about 4.4 to 4.6 billion years old.
Astronauts on Moon
Lunar Rocks
Unlike the Earth, the Moon does have rocks that are
remnants of the early formation of the solar system.
Radiometric dating: The oldest lunar rocks have been
found to be about 4.4 to 4.5 billion years old.
The Moon
Maria
Craters
Highlands
Origin
of the
Solar
System
Origin of the Solar System
Nebular Hypothesis:
The orderly nature of our
solar system leads
astronomers to conclude
that all of the planets
formed at essentially the
same time and from the
same primordial material
as the sun.
Origin of the Solar System
Nebular Hypothesis:
The planets formed from the
accretion of tiny particles
that condensed out of a
primordial solar nebula.
This hypothesis was proposed
by the German philosopher
Immanuel Kant in 1755, and
was also proposed by the
Fench mathematician Pierre
Simon LaPlace in 1796.
Origin of the Solar System
Nebular Hypothesis:
The planets formed from the
accretion of tiny particles
that condensed out of a
primordial solar nebula.
Between about 5.0 billion
years ago and about 4.6
billion years ago: The solar
nebula condensed into a
number of discrete clusters
of mass that eventually
formed into the planets.
Solar System
Meteorites
Age of the Earth
Oldest Rocks
on Earth
3.9 - 4.0
Billion Years
4.6
Billion
Years
Evidence from meteorites and lunar rocks leads scientists to
conclude that the Earth and the other planets were formed about
4.6 billion years ago.