Origin of Life -
Was it an astrobiological event
or chemical evolution ?
Did
Minerals play a Role
in Chemical Evolution?
work of Robert Hazen at Carnegie Institute (Geophysical Lab)
Current Paradigm...
evidence favors a chemical evolutionary origin of life
"simple chemical self-assembly has lead to self-replicating systems"
Earth forms 4.5 billion years ago
from 4.5 to 4.0 bya - Asteroids bombard & sterilize planet surface
4.0 bya - first fossil evidence of microscopic life
Initial event may have been evolution of
Carbon based molecules
ancient atmosphere (was reducing) with single carbon gases
carbon monoxide, carbon dioxide, methane
next
1953 - Miller & Urey @ U Chicago
recreate ancient atmosphere [ammonia,
methane, water, &
electricity]
produce amino acids, which many assume can now link into complex polymers
rocky surfaces allow concentration via evaporations
§ Origin of Life research is no longer philosophical, but rather experimental
1977
- discovery of deep hydrothermal vents
suggests that origin of life organic reactions
may have occurred in intense
heat & pressure of
these vents
Hazen's lab designed experiments to
mimic high temp/pressure of
hydrothermal vents
& look at the role minerals may have played in producing
self-replicating molecules
next
ROLE of MINERALS -
minerals (calcite,
feldspar,
magnetite,
clay, etc...)
may have fostered organic chemistry of early life.
1998 - began in
Robert Hazen's lab
[Carnegie Institute, Washington]:
showed that amino acids decompose at 200
oC under pressure,
but when
FeS
(iron-sulfur) minerals are added, amino acids
remain intact.
the ROLE of MINERALS is one of SCAFFOLDING SUPPORT
by the minerals...
an easy way to assemble molecules in dilute solution is to
concentrate the molecules
on a
flat surface,
which is exactly what minerals may have helped provide:
feldspar* -
a tectosilicate
mineral
that houses microscopic pits that could shelter life's
precursor
molecules from UV radiation and destruction...
allows concentrating
of components
and greater chemical reactivity
magnetite* (iron oxide) - triggers combination of nitrogen & hydrogen
into
ammonia (NH3), a reduction reaction essential for organic life
next
clay* - layered clays can
trap organics [helps concentrate
them] between clay sheets;
held close together molecules can
then form more complex molecules...
montmorillonite clays can sharply accelerate the formation of
membranous
fluid-filled sacs;
these vesicles can grow and undergo a simple form of division, giving them
properties akin to primitive cells & might be a mechanism that helped create
RNA
molecules enclosed in a membrane?
Minerals may provide some possible answers to
one chemical
anomaly:
the selection of only 1 specific optical isomer [
L-amino acids
]
out of 2 (D &
L)
enantiomers*
in the making
of cellular proteins... today's proteins contain
only L-amino acids.
Miller's experiments produces
50-50 mix of
the 2 isomers, the D &
L amino acids...
Could the Earth's minerals have help select one
isomer over the other isomer?
calcite*
-
calcium
carbonate mineral that attracts
D &
L- amino acids isomers
to
different crystal faces,
thus in the origin of life
one
amino acid isomer could have been selected over the other.
next
Pre-Biotic Chemical
Evolution (current
paradigm)
origin of life was
not a single event...
it was most likely a
gradual sequence of modest chemical
compound formations,
which added a degree of
order and
complexity to molecular structure.
1st step - abiotic formation of building blocks...
either ala...
Miller & Urey or
hydrothermal vents
or via 'space debris'
2nd step -
minerals provide structural basis for
concentrating,
confining, ordering, & selecting molecules;
may have lead to first
primitive self-replicating molecular systems
next step - competition for limited
chemical resources leads to...
MOLECULAR NATURAL SELECTION
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