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Nucleosythesis
Life: DNA – proteins – amino acids - water
Question - where did they come from in the
first place ?
Need to take a step back
Waaaaaaay back……..to
The Big Bang!!!!
Big Bang Basics
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Universe emerged from a single spot out of nothing. Universe is currently
thought to be 13.7 billion years old.
Decoupling of matter from radiation at about 379,000 years to form
protons and electrons
Radiation seen today as microwave background radiation
Most of early universe made of about ¾ hydrogen, ¼ helium and
trace (.000,000,001) of lithium. No elements produced with an
atomic number higher than lithium !!!!!!
Heterogeneous universe from a homogenous one ?
Quantum fluctuations in early universe produced “framework” of galaxy
formation. Attracted gas and dark matter that coalesced to form first
galaxies at only 500 million years. Formed in “cosmic web”.
Large Scale Structure of Universe
How did we get here from there?
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Nuclear Fusion - nucleosynthesis
Stars form mutual gravitational attraction of
original matter from Big Bang into clumps
called protostars.
Hysdrostatic equilibrium is established where
outward radiation pressure balances gravity.
A Star is born!
Early stars had very little metallicity (i.e. no
heavy elements).
Stellar evolution - (main sequence) – Life
cycle of a star depends on it’s size
Small stars – last a long time – perhaps longer
than the universe.
Larger stars – burn through their fuel faster –
most of the first stars were large stars that
burned up quickly and then exploded.
Creation of the “heavy” elements
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Star will fuse elements into different elements with
higher atomic numbers until it reaches iron. Iron
does not “burn”
Mediums star (sun) will shed most of its
accumulated matter into a planetary nebula.
Larger suns will supernova – creates all elements
heavier than iron by an intense burst of nuclear
reactions that typically last mere seconds during
the explosion of the supernova core. Scatters
elements into cosmos into giant clouds.
All elements heavier than Lithium are formed in
the heart of stars.
Planetary nebula
Supernova
You are Stardust
Formation of Solar System
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Solar system began with collapse of a giant
molecular cloud approx. 4.5 billion years ago.
Disturbance by supernova ? Disturbed
equilibrium of cloud.
As it collapsed it gained angular momentum.
Proto-planets began forming.
10 million Kelvin – fusion reaction started
Cleared out inner solar system of volatiles –
left the rocky worlds.
Frost line at asteroid belt.
Gas giants kept their volatiles.
Accretion Disk
Formation of Planet Earth
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4.6 BY - Formation of the approximately homogeneous solid Earth
by plantiesmal accretion
4.3 BY - Melting of the Earth due to radioactive and gravitational
heating – most heavy elements sink to core.
Outgassing of molecules such as water, methane, ammonia,
hydrogen, nitrogen, and carbon dioxide
4.0 BY - Bombardment of the Earth by planetesimals stops.
3.8 BY – the Earth’s crust solidifies – formation of the oldest rocks
found on Earth.
3.5 BY Single cell life develops.
Implication was that as soon as life COULD exist it did.
Early Earth was a Rough
Neighborhood