the primordial earth hadean and archean eons

THE PRIMORDIAL EARTHHadean and Archean Eons

THE PRIMORDIAL EARTHHadean and Archean EonsFormation of the Solar System

The Solar Nebula Hypothesis




1. Planets revolve around sun in same directionCounter-clockwise




2. Planets lie roughly within sun's equatorial plane (plane of sun's rotation)




3. Solar system is disk-like in shape




4. Planets rotate CCW on their axes, except for: a. Venus - slowly CW b. Uranus - on its side c. Pluto - on its side




5. Moons go CCW around planets (with a few exceptions)




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




7. Age - Moon and meteorites 4.6 billion years




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).




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 EARTHHadean and Archean EonsMeteorites

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)


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)


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


Types of Meteorites

3. Achondrites - stony meteorites without chondrules, resembling basalt


Types of Meteorites

4. Iron meteorites Iron-nickel alloy

a. Coarse-grained intergrown crystal structure (Widmanstatten pattern)

b. About 5% of all 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.

Hadean Eon 3.8-4.6 byBP

Archean Eon 2.5-3.8 byBP

Proterozoic Eon 0.54-2.5 byBP

THE PRIMORDIAL EARTHHadean and Archean EonsAccretion and DifferentiationOrigin of the Earth's Internal Layering

1. Solar Nebular Theory or Cold Accretion Model(secondary differentiation):

Earth was originally homogeneous.

THE PRIMORDIAL EARTHHadean and Archean EonsAccretion and Differentiation

Origin of the Earth's Internal Layering

Earth formed by accretion of dust and larger particles of metals and silicates.



Origin of layering requires a process of differentiation.



Differentiation is the result of heating and at least partial melting.



Iron and nickel sink to form core.



Less dense material (silicon and oxygen mixed with remaining iron and other metals) forms mantle and lighter crust (primarily silicon and oxygen).



Presence of volatile gases on Earth today indicatesthat complete melting did not occur.


Source(s) of heat for melting?

1. Accretionary heat from bombardment

THE PRIMORDIAL EARTHHadean and Archean EonsManicouagan Crater, Quebec 206-214 myBP


Chicxulub (Mayan Tail of the Devil, Mexico)Cretaceous-Tertiary (K-T) Boundary

THE PRIMORDIAL EARTHHadean and Archean EonsBarringer Crater, AZ 49,000 yBP

Tunguska, Siberia 30 June, 1908


Samuel Taylor ColeridgeThe 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




2. Heat from gravitational compression



3. Radioactive decay


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 EARTHHadean and Archean EonsThe 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 EARTHHadean and Archean EonsThe Hadean Crust

THE PRIMORDIAL EARTHHadean and Archean EonsEarly Continental Crust

THE PRIMORDIAL EARTHHadean and Archean EonsModern Crust

THE PRIMORDIAL EARTHHadean and Archean EonsEvolution 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.


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


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

Second AtmosphereProduced 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).


the primordial earth hadean and archean eons

Documents

archean eonsformation

solar wind

solar system objects

jovian planets

terrestrial planets

asteroids moon rock

accretion of matter

protoplanets cold accretion