Early Evolution of Life
Life on Earth originated
between 3.5 & 4.0 bya
Origin of earth
crust solidified
Oldest evidence of life - stromatolites
The first cells may have originated
by chemical evolution on a young
Earth.
Based on protobiont evolution
Process:
abiotic synthesis & accumulation of small
organic molecules
joining of monomers into polymers
formation of protobionts
origin of heredity
Abiotic synthesis of organic
monomers is a testable hypothesis
Formation of monomers
Oparin’s Hypothesis
Miller’s Experiment
Abiotic synthesis of organic
monomers is a testable hypothesis
Laboratory simulations of early Earth
conditions have produced organic
polymers.
protenoids - definition
known that small
organic molecules
polymerize when they
are concentrated on
hot sand, rock, clay
Protobionts can form by
self-assembly
Organic molecules synthesized in the lab
have spontaneously assembled into a variety
of droplets with some properties associated
with life.
microspores
Protobionts can form by
self-assembly
Organic molecules
synthesized in the lab
have spontaneously
assembled into a
variety of droplets
with some properties
associated with life.
liposomes
Protobionts can form by
self-assembly
Organic molecules
synthesized in the lab
have spontaneously
assembled into a
variety of droplets
with some properties
associated with life.
coacervates
RNA was probably the
first genetic material.
The first genes may have been abiotically
produced RNA, whose base sequence served
as a template for both alignment of amino
acids and polypeptide synthesis & alignment
of complementary nucleotide bases in a
primitive form of self-replication.
RNA was probably the
first genetic material.
Why genes?
RNA was probably the
first genetic material.
how genes operated
RNA was probably the
first genetic material.
polymers of RNA have been produced
abiotically
RNA can act as catalysts
ribozymes
The origin of hereditary information
made Darwinian evolution possible
Once genetic information became
incorporated inside membrane-enclosed
compartments, protobionts would have
acquired heritability and the ability to evolve
as units.
The origin of hereditary information
made Darwinian evolution possible
Process
protobiont incorporates genetic information into the aggregates of
molecules
selectively accumulates monomers from surroundings & uses enzymes
programmed by genes to form polymers and carry out chemical
reactions
grows, splits, distributes copies of genes to offspring
Even if one protobiont survived, its descendants would vary because
of mutations (copying errors)
The origin of hereditary information
made Darwinian evolution possible
Differential reproductive success of varying
individuals led to accumulated refinements to
primitive metabolism & inheritance.
Example - evolution of DNA from RNA
Debate abounds
regarding origins
Was abiotic synthesis of organic molecules
necessary first step?
Panspermia
Debate abounds
regarding origins
Challenge to RNA world of evolution
self-replication of RNA difficult
some simple organic molecules are capable
of self-replication - perhaps something
similar preceded the gene
Debate abounds
regarding origins
Site of evolution
shallow water vs. deep-sea vents
Debate abounds the
origin of life abounds.
RNA as genetic material