Transcript Origins (Chapter 1)

Origin of the Universe, Matter, Elements and
Nucleosynthesis
Matter and the Origin of Elements:
•Much of what we know today of the distant past is
secondhand information.
•Elementary particles and chemical elements are ashes
of star explosions.
•Background radiation known from FOUR regions of
the electromagnetic spectrum; radio waves,
microwaves, x-rays and gamma rays. These are
remnants of special events.
•The background of the radio sky are uniform and
basically the sum total of all universal radio emissions.
•Penzias and Wilson won the Nobel Prize in 1978 for
work on 3K microwave background radiation, redshifted remnants of photons moving away from 3000K
flash.
Microwave, 3K, background came into existence ~
500,000 years after Big Bang.
Hubble- Light from distant galaxies is progressively redshifted so that photons are observed with energies lower
than those their point of emission.
1 photon = hv where h = Plank’s constant and v =
frequency of radiation s-1
SUN
The sun derives its
energy through
thermonuclear
processes-fusion reactor
in the core. In principle
2 protons collide
forming deuterium and
emit 1 positron and a
neutrino. The
deuterium nucleus will
pick up 1 proton to form
He3 and emit a gammaray photon. Two of the
He3 nuclei will combine
to form He4 plus the
release of 2 protons.
•Radiogenic nuclides are those that
decay by emission of alpha, beta and
gamma radiation - or by electron
capture.
•The periodic table contains 92
elements of which 90 are known
from earth. Technetium (Tc)-from
stars and Promethium (Pm) from
stars.
•By bombarding an element with
neutrons of fast-moving protons it is
possible to synthesize elements with
atomic numbers above 92
(transuranium elements)
•Among the stable nuclei
generated the course of less
than 3 minutes, deuterium,
He-3, He4, Li-7
•The essential protons and
neutrons needed for the
synthesis of elements were
believed to be generated
when the Universe was a
few seconds old.
•More stable and eventually
became most prominent, H
and He-4
•The remainder of the 90
elements have their origin
in stars-during birth and
death.
•When He reserve was
exhausted, Red Giants -all H
to He then gravitational
contraction of He core which
raise the density and
temperature and He is ignited.
•Dying stars that have cooled
off - known as White Dwarfs
•Supernova- rapid collapse of
star-with rapid increase in
temperature, an explosion.
•Nuclear fusion up to Fe,
Fe56 is very stable
•Fusion of 2 Si28 via
Ni56 +Co56
intermediates
Solar System
•~ 95% of the mass
in our galaxy resides
in the stars though
the rest is interstellar
dust.
•Clouds circle
around a galactic
center and pick up
gases and particles
that were previously
ejected from dying
stars.
•Expansion due to
pressure of the gases
and contraction - due
to gravitation will
affront the critical
mass of the
interstellar cloud.
Magnetic fields from within
or outside the cloud
complex could trigger a
collapse.
Supernova explosions in
the vicinity of a cloud
might generate large shock
waves and cause the cloud
to collapse. Isotope records
in lunar and meteoritic
material strongly suggest
that some isotope anomalies
are caused by supernova
events.
They type of events are
believed to be responsible
for triggering the collapse
of the interstellar cloud that
produced our solar system.
• The fusion of hydrogen atoms
into helium (i.e., star birth) is
known as the T-Tauri Event!
• simultaneously, particles of the
surrounding disc collide and
form larger particles
• particle aggregates collect mass
and form 'planetismals' or
protoplanetary discs
• onset of fusion (star formation, or
the T-Tauri Event) results in
energy release
• energy release pushes gas and
dust out of the solar nebula
• loss of gas and dust prevents
further accretion of
• rotational motion of the
protoplanets eventually slows,
and orbits stabilize
• Formation of the Earth:
• theory of nebular formation explains the
development of the Earth's solar system
• planetary formation took place ~4.6 billion
years ago
• proto-Earth accumulated dust, gas, debris
prior to the 'birth' (T-Tauri) of the sun
• clearing of nebular matter by solar winds
permitted warming of planetary surface
• resulted in the volatilization of certain
compounds – H, He, NH3, CH4, H2O
• intense internal planetary heating
occurred simultaneously
• decay of radioactive elements (U, K, Rb) in
the newly formed earth produce heat
• also heat energy release associated with
particle collisions (compression)
• resulted in melting of the planetary
interior and segregation of elements
• heavier elements (Fe, Ni) sank while
lighter elements (Si) floated upward
Following completion of
planet formation, the
remaining planetesimals
were destroyed by heavy
bombardment that lasted
for 0.5 billion years.
Craters on moon are a
vivid display of “terminal
lunar cataclysm” which
peaked 3.9 billion years
ago. Also well preserved
on Mercury-on earth,
most of this evidence has
been weathered away.
•More than 95% of all the mass
retained by the solar system is
collected by the proto-sun which is
the remaining 5% proto-planets
and proto-moons.
•As the proto-sun collapsed the
core temperatures were raised to a
point of ignition. This caused an
outburst of energy (T-Tauri wind),
swept the atmosphere (H & He) of
the terrestrial planets (Mercury,
Venus, Earth, Mars) away.
•By contrast the 2 largest planets,
Jupiter and Saturn, retained their
atmosphere, Uranus and Neptune
lost ~ 90% and there is not enough
information on Pluto. There is
some speculation that Pluto is a
comet of sorts (Giant Dirty
Snowball)
EVOLUTION OF EARTH’S
ATMOSPHERE AND HYDROSPHERE
Past theories have suggested as the Earth accreted,
cooled, and the atmosphere was formed from
outgassing from the interior.
Based on noble gas content of atmosphere for example
- If primitive Earth contained atmosphere, expect that
its gases would be similar to cosmic abundance
Ne20: no production by radioactive decay, too heavy to
escape, and it is inert.
Using other gases that may have also been
retained can calculate expected mass:
Cosmic = N/Ne = 5.33
If, present day atmospheric mass of Ne =16 x
1016g is all from primary sources, 5.33 x 6.5
x1016g should yield mass of N that is also from
primary sources.
However, the product (35 x 1016g) is less than
the current amount of N (38 x 1020g). This may
suggests that the atmosphere formed later in
time.
Perhaps a steam
atmosphere existed
during the accretionary
phase ~ 100 mya
Cooling and heating
during impacts, ocean
may have started to
form numerous times.
If steam atmosphere
existed -T(tauri) wind
might have swept
volatiles away during
proto-sun collapse
If so, comets and
asteroids that impacted
Earth during “terminal
lunar cataclysm” may
have brought volatile
inventory.
•Once the primary accretion endedmost of the water vapor would
have condensed to form oceans leaving atmosphere dominated by
C compounds mostly CO2, CO and
N2
•Free oxygen absent, except at high
altitudes via photo-dissociation of
CO2 + H2O
•Exactly how much CO2 was
present in early atmosphere is
uncertain.
Conversion of silicate minerals to
carbonates
Crustal abundance of C in
carbonates 1023g
•Earliest sedimentary rocks 3.8
(bya)
• Development of
Planetary Life:
• Miller and Urey (1953)
suggested a process
known as 'biosynthesis'
• synthesis of amino acids
through energy
activation (e.g.,
lightning strikes)
• early oceans contained
the building blocks of
amino acids – H20,
CH4, H, and NH3
Flux of Solar UV
Radiation
•Ozone was also absent
•Formation of large
complex molecules
destroyed by UV.
•Formation of organic
compounds?
•Importance of Sulfur
photochemically volcanoes would have
emitted sulfur
The ocean was probably
formed along with the planet
and could have been close to
its volume at 4.5 bya - pH
and composition very
different.
Deep Ocean pH and
composition~8
An ocean underlying an
anoxic CO2 rich atmosphere
should have been different
in composition, FeS2 would
not be oxidized
A dense CO2 atmosphere
HCO3 would be in
equilibrium with this, thus
the bicarbonate might be
comparable to chloride.
“Soda Ocean” Concept
•High pH and high pCO2
very high HCO3- probably
much saltier
•Low Ca and Mgprecipitated up in dissolved
•Alkalis mostly Na and K
served as counter ions for
bicarbonate
•Soda ocean like worlds
largest carbonate lakesLake Van
•These lakes hold
dissolved carbonates
that exceed ocean
bicarbonates by 1000 x
before sodium
carbonate precipitation
PREBIOTIC
SYNTHESIS
Energy sources:
Sparks source
most extensively
investigated.
Not formed
directly in electric
charge but resulted
from several
reactions of
smaller molecules.
1969
carbonaceous
chondrite, large
amount of amino
acids
Now recent
information on
interstellar
molecules:
CH2O,
HCN, CH3CHO,
HC2CN
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oldest fossils (anaerobic organisms) date to
~3.5 billion years ago
– graphite concentrations (carbon) in
many sedimentary rocks
– stromatolites (mats of cyanobacteria
or blue-green algae)
microbial life lacking a nucleus
(prokaryotes) – each cell chemically selfsufficient
many microbes flourished in the hot oceans,
probably around volcanic vents
metabolized hydrogen-rich compounds
and/or organic materials to derive energy
– sulfate reducing bacteria that produce
H2S
– fermentative bacteria that produce
CO2 and alcohols
– methanogenic bacteria
reduced meteoric bombardment allowed
anaerobic microbes to diversify
many adapted to new biological niches –
some on land – but stayed single celled
~2.8 billion years ago bacteria
(cyanobacteria) developed photosynthetic
ability
photosynthesis produced O2 which was
released into the oceans and atmosphere
rise in atmospheric O2 levels occurred
between 2.4 and 1.8 billion years ago
Faint Sun and Decline of
CO2
High CO2 counteracted
climatic effects of a faint
sun. Loss of CO2 as
carbonates weathered
Free oxygen absent until
about 2 bya
Disappearance of uraninite
and pyrite deposits and
appearance of “Red Beds”
Deep ocean still anoxic
based on banded iron
formations BIFs (ferrous
iron)
As O2 increased so did
ozone, decreasing UV early
Proterozoic proliferation of
phytos 2 bya
Earth inhabited by
life at start of
sedimentary record
3.8 bya
Biosedimentary-3.5
bya stromatolites
Sedimentary
organic carbon and
derivatives:
Kerogen and
graphite
molecular oxygen in air
and water became
abundant by ~2.3
billion years ago
• accompanied by
conversion of a
fraction of the O2 into
a tri-atomic form
• known as ozone
(O3)
• formed a
protective layer in
the atmosphere
(reduced
ultraviolet
radiation)
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eukaryotic metabolism
began after O2 had
risen ~1% of its
present abundance
probably occurred ~2
billion years ago,
according to the fossil
record