Transcript The Proterozoic Eon

THE PRIMORDIAL EARTH
Hadean and Archean Eons
Formation of the Solar System
The Solar Nebula Hypothesis
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Formation of the Solar System
The Solar Nebula Hypothesis
1. Planets revolve around sun in same direction
Counter-clockwise
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Formation of the Solar System
The Solar Nebula Hypothesis
2. Planets lie roughly within sun's equatorial plane
(plane of sun's rotation)
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Formation of the Solar System
The Solar Nebula Hypothesis
3. Solar system is disk-like
in shape
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Formation of the Solar System
The Solar Nebula Hypothesis
4. Planets rotate CCW on their axes, except for:
a. Venus - slowly CW
b. Uranus - on its side
c. Pluto - on its side
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Formation of the Solar System
The Solar Nebula Hypothesis
5. Moons go CCW around planets
(with a few exceptions)
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Formation of the Solar System
The Solar Nebula Hypothesis
6. Distribution of planet densities and compositions is
related to their distance from sun
Inner, Terrestrial planets have high density
Outer, Jovian planets have low density
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Formation of the Solar System
The Solar Nebula Hypothesis
7. Age - Moon and meteorites 4.6 billion years
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Formation of the Solar System
The Solar Nebula Hypothesis
Cold cloud of gas and dust, contracts, flattens,
and rotates.
Turbulence in cloud caused matter to collect in
certain locations.
Accretion of matter around central mass to form
protoplanets (cold accretion).
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Formation of the Solar System
The Solar Nebula Hypothesis
90% of mass to center.
Cloud condensed, shrank, and heated by gravitational
compression to form Sun.
Solar wind drove lighter elements outward causing
observed distribution of masses and densities.
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Meteorites
Meteorites are chunks of rock from the solar system
that have impacted the Earth.
They include fragments of the following objects that
were broken off by collisions with other solar system
objects:
1. Asteroids
2. Moon rock
3. Planets, such as Mars (Martian meteorites)
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Meteorites
Types of Meteorites
1. Ordinary chondrites
a. Most abundant type of meteorite
b. About 4.6 billion years old,
c. May contain chondrules (spherical bodies that
solidified from molten droplets thrown into space
during solar system impacts)
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Meteorites
Types of Meteorites
2. Carbonaceous chondrites
a. Contain about 5% organic compounds, including
amino acids (building-blocks of proteins, DNA,
and RNA)
b. May have supplied basic building blocks of life to
Earth
c. Contain chondrules
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Meteorites
Types of Meteorites
3. Achondrites - stony meteorites without chondrules,
resembling basalt
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Meteorites
Types of Meteorites
4. Iron meteorites
Iron-nickel alloy
a. Coarse-grained intergrown crystal structure
(Widmanstatten pattern)
b. About 5% of all meteorites
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Meteorites
Types of Meteorites
5. Stony-irons
Composed partly of Fe, Ni and partly of silicate
minerals, including olivine (like Earth's
mantle).
a. About 1% of all meteorites.
Least abundant type.
Proterozoic Eon 0.54-2.5 byBP
Archean Eon 2.5-3.8 byBP
Hadean Eon 3.8-4.6 byBP
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Accretion and Differentiation
Origin of the Earth's Internal Layering
1. Solar Nebular Theory or Cold Accretion Model
(secondary differentiation):
Earth was originally homogeneous.
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Accretion and Differentiation
Origin of the Earth's Internal Layering
Earth formed by
accretion of dust and
larger particles of
metals and silicates.
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Accretion and Differentiation
Origin of the Earth's Internal Layering
Origin of layering requires a process of differentiation.
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Accretion and Differentiation
Origin of the Earth's Internal Layering
Differentiation is the result of heating and at least
partial melting.
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Accretion and Differentiation
Origin of the Earth's Internal Layering
Iron and nickel sink to form core.
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Accretion and Differentiation
Origin of the Earth's Internal Layering
Less dense material (silicon and oxygen mixed with
remaining iron and other metals) forms mantle
and lighter crust (primarily silicon and oxygen).
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Accretion and Differentiation
Origin of the Earth's Internal Layering
Presence of volatile gases on Earth today indicates
that complete melting did not occur.
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Accretion and Differentiation
Source(s) of heat for melting?
1. Accretionary heat from bombardment
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Manicouagan Crater, Quebec 206-214 myBP
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Accretion and Differentiation
Chicxulub (Mayan Tail of the Devil, Mexico)
Cretaceous-Tertiary (K-T) Boundary
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Barringer Crater, AZ 49,000 yBP
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Tunguska, Siberia 30 June, 1908
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Samuel Taylor Coleridge
The Rime of the Ancient Mariner:
The upper air burst into life!
And a hundred fire-flags sheen,
To and fro they were hurried about!
And to and fro, and in and out,
The wan stars danced between
And the coming wind did roar more loud,
And the sails did sigh like sedge;
And the rain poured down from one black cloud;
The Moon was at its edge
may have been inspired by the Leonid meteor shower that he witnessed in 1797
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Accretion and Differentiation
Source(s) of heat for melting?
2. Heat from
gravitational compression
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Accretion and Differentiation
Source(s) of heat for melting?
3. Radioactive decay
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Accretion and Differentiation
2. Hot Accretion Model - (primary differentiation):
Originally hot, heterogeneous Earth
Zoning developed during cooling
High-temperature crystallization elements
(Fe, Ni) cool first and form Earth's core
Low-temperature crystallization (Si, O)
elements cool late to form Earth's crust
THE PRIMORDIAL EARTH
Hadean and Archean Eons
The Hadean Crust
Dominated by iron and magnesium silicates.
If Earth experienced heating and partial melting,
it may have been covered by an extensive magma
ocean in the Hadean.
Magma cooled to form rocks called komatiites.
Komatiites form at temperatures greater than those
at which basalt forms (greater than 1100oC).
Komatiites are ultramafic rocks composed mainly of
olivine and pyroxene.
Formed Earth's Hadean crust.
THE PRIMORDIAL EARTH
Hadean and Archean Eons
The Hadean Crust
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Early Continental Crust
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Modern Crust
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Modern Crust
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Evolution of the Atmosphere
First Atmosphere
Earth's atmosphere has evolved or changed over time.
Earth's first, primitive atmosphere lacked free oxygen.
The primitive atmosphere was derived from gases
associated with the comets and meteorites
which formed the Earth formed during accretion.
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Evolution of the Atmosphere
First Atmosphere
Composition - Probably H2, He
These gases are relatively rare on Earth compared
to other places in the universe and were probably
lost to space early in Earth's history because
Earth's gravity is not strong enough to hold
lighter gases
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Evolution of the Atmosphere
First Atmosphere
Earth still did not have a differentiated core
(solid inner/liquid outer core) which creates
Earth's magnetic field
(magnetosphere = Van Allen Belt) which deflects
solar winds.
Once the core differentiated the heavier gases could
be retained
THE PRIMORDIAL EARTH
Hadean and Archean Eons
Evolution of the Atmosphere
Second Atmosphere
Produced by volcanic out gassing.
Gases produced were probably similar to those
created by modern volcanoes
H2O, CO2, SO2, CO, S2, Cl2, N2, H2, and
NH3 (ammonia) and CH4 (methane)
No free O2 at this time (not found in volcanic gases).