SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCES
Intro Cell & Molecular Biology (BIOL 210); Instructor: Elmar Schmid, Ph.D.
Origin of life theories & Evolutionary theory
“Oh, in truth, at that moment I deprived the culture medium of the only thing
not given to man to produce (… life).”
L. Pasteur, 1864

There is more than 2 million different forms of life on planet earth today and we have to
assume (based on fossil records and other found traces of life) that there existed an
even greater number of different life forms in the millions of years before us

Even though modern science is still not able to explain how life got on this planet, it
offers a series of intellectually very interesting theories, or origin of life theories,
which are strongly founded on important experimental observations and which will be
laid out in some detail in this chapter

A significant body of scientific evidence shows that life is on earth since approximately 1
billion years and strongly supports the idea that primitive life forms may have existed on
earth as early as 3.5 - 4 billion years ago

during this tremendously vast period of time life may have evolved from primitive precellular structures and out of a “molecular broth” (see “theories on the origin of life” in
the sections below) into millions of genetically and morphologically different species
which call this fascinating blue planet home
 today 2 million different species are known to live on Earth and they
populate almost all regions on this life-supporting planet

early biologists, most prominently Karl von Linne, started to classify the huge variety of
species into so-called taxa and introduced the first taxonomic system into biology;
 this early taxonomic system was primarily based on morphological characteristics,
i.e. existence or absence of certain body features; body shape, etc. in biological
organisms

with the discovery of DNA, the isolation of proteins and other biomolecules, together
with the introduction of a plethora of molecular biological techniques e.g. DNA
sequencing, protein sequencing, chromosome analysis, NMR analysis, karyotyping, etc.
and the establishment of comprehensive DNA and protein data bases, modern
biologists started to classify organisms based on their molecular similarities, e.g. DNA
homologies, protein sequence similarities, rather than due to their morphological
characteristics
- most of the existing “traditional” phylogenetic trees and relationships are challenged
these days by new findings or these new approaches

today, all existing species on our planet are classified into the so-called five major
kingdoms of organisms

for each of these 5 kingdoms a so-called phylogenetic tree has been developed on the
basis of morphological and genetic features of each of its members
1
SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCES
Intro Cell & Molecular Biology (BIOL 210); Instructor: Elmar Schmid, Ph.D.

the five kingdoms of living organisms on planet Earth are:
1.
2.
3.
4.
5.
Bacteria
Protista
Fungi
Planta
Animalia

As different as all these different forms of life might be on the tissue land organ level
and regarding their intricate body morphologies, “deep down” they all share a plethora
of structures and molecules on the cellular and molecular level, such as ATP, DNA,
RNA, proteins made up from amino acids, and phospholipids-made cell membranes
and organelles

This modern day information is important in the critical and fair evaluation of
contemporary and also future theories about one of the most challenging questions to
be answered in the biological science; the question about where life came from, how it
established itself on planet earth and how it turned itself into one of the great wonderful
success stories in this known universe with more than 2 million different life forms today
Origin of Life Theories

Indeed, the question of how and when life arose on planet Earth has fueled the scientific
discussion and our imagination ever since the dawn of human mankind, the evolution of
the human brain and conscience

the origin of life on Earth has been dated back to 3.5 – 4.0 billion years; the earliest,
morphologically primitive life forms appear in certain rock formations during that time
period
- various fossil records of the Precambrian period (4,600 – 600 Mio. years ago)
have been found in certain geological rock formations (see Images below)
- the images below show fossilized cyanobacterial colonies, so-called stromatolithes
(left panel) as well as fossilized images of filamentous (top right) and colonial (top
bottom) photosynthetic cyanobacteria (e.g. Gloeocapsomorpha), which have been
found in 1- 3 billion year old Archean rock formations, e.g. in West Australia (Bitter
springs chert)
 they were identifiable by chemical breakdown products of their
photosynthesis pigments (“chemical fossils”)
- further evidence comes in form of Pisolites, which are small concentrically layered
structures of fossilized bacteria
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SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCES
Intro Cell & Molecular Biology (BIOL 210); Instructor: Elmar Schmid, Ph.D.
filamentous cyanobacterium
Palaeolyngbya
Layered stromatolite
(= calcium carbonate precipitate)
colonial chroococcalean
cyanobacterium
( 850 mya)

but how and under which circumstances did already complex organized and structured
life get there?

Speculation about the true origin of life and where life comes from has a long human
history and can be traced back to the early human civilizations (for an overview see the
Graphic below)
3
SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCES
Intro Cell & Molecular Biology (BIOL 210); Instructor: Elmar Schmid, Ph.D.
Origin of Life Theories & Milestone Discoveries
Molecular
Biology
Organic Chemistry
Alchemy
Microbiology
Graphic©E.Schmid/2003
Ancient Times
1700
1800
1861
1828
“life arose from
non-living matter”
(Aristotle)
“Molecular
Evolution Theory”
(M. Eigen,
L. Orgel)
Proteinoid
Microspheres
(S. Fox)
“Phlogiston
Theory”
(J. Becher,
G. Stahl)
“Vitalism
Theory”
(G. Stahl)
1850
Synthesis
of glycine
(W. Loeb,
Klages, et al.)
Chemical synthesis
of urea
(F. Woehler)
 from silver cyanite &
Ammonium chloride
 vis vitalis exists
1900
Synthesis
of alanine
(Strecker)
Synthesis
of sugar
(Butlerov)
1970s 2000
1938 1953 1980s
Miller-Urey
Experiment
(S. Miller)
“RNA world theory”
Ribozymes
(T. Czech)
“life begets
life”
(Virchov,
Pasteur)
“Anoxic
Early Earth
Atmosphere
Theory”
(A.I. Oparin,
J.B.S. Haldane)

in aanncciieenntt ttiim
meess, the Greek philosopher Aristotle speculated that life arose from nonliving matter
- when Aristotle introduced his “spontaneous generation” idea, he together with
other thinkers of his time, such as Democritus and Epicurus, had no doubt that life
naturally originated from inert, inorganic matter

The concept of spontaneous generation was widely accepted and unquestioned far into
the middle of the 17th century and was supported by some of the thinkers, teachers and
scholastics of the Church, including Saint Basil (329 – 379), Saint Augustine, Saint
Thomas of Aquinas as well as naturalists like J.B. van Helmont
- since the existence and true nature of seeds, egg cells and molecules has not been
discovered yet, it was common believe that flies and maggots form from components
of rotten meat by spontaneous generation and that bacteria are directly created form
broth components over time

In 1668, the Italian physicist Florencia Francisco Redi (1626 – 1697) performed his
famous maggot experiment which experimental outcome lead to serious doubts about
the correctness of the upheld spontaneous generation idea of his time
- he used two glass containers in both of which he brought pieces of meat; while he
left the neck of one of the vials open, he blocked the entry into the second vial by
placing some loose cotton wool
4
SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCES
Intro Cell & Molecular Biology (BIOL 210); Instructor: Elmar Schmid, Ph.D.
-
maggots only developed in (and flies only flew out of) the first vial, while no insect
development occurred in the second container
the maggots must have got there by some inoculation by flies (which as we know
today) laid their eggs into the piece of meat

Around the 1700s, the Italian physician Antonio Vallisnieri (1661 – 1730) proved that
hatched insects from plant galls derive from previously laid eggs into the plant tissue,
which later on grew in size and helped to nourish the developing caterpillars of the
insect
- this careful observation gave a further argument against the popular spontaneous
generation theory

in the 1177ttthhh cceennttuurryy, the German physicians and university professors J. Becher and G.
Stahl develop the so-called “Phlogiston theory” (from the Greek word phlogistos =
burning) to explain chemical combustion reactions
- Stahl further believed living matter contained a “soul” (vis vitalis) that differed in
composition from nonliving matter (“Vitalism theory”)
- He and many generations of vitalism supporters after him searched without success
to collect the phlogiston and to find proof for the “mysterious life force” in living
beings

until the m
miidd--11880000''ss scientists widely accepted the Vitalism theory and generally
believed that organic (= carbon-containing) chemicals could only form through living
things and with the help of a mysterious “vital force”

in 11882288, the German chemist Friedrich Woehler synthesizes the first organic
compound, called urea, from silver cyanite and ammonium chloride, two purely
inorganic materials; his ground-breaking chemical experiment disproved the dominating
Vitalism theory of his time

Lingering doubts on the validity of the experimental design of the experiments which
claimed to disprove the spontaneous generation idea were put aside when the great
French scientist Louis Pasteur (1822 – 1895) conducted his famous experiment at the
Paris Academy of Sciences
- after heating the nutritional broth in the bulb of his designed swan neck flask, no
bacterial growth and life arose in the open flask after even extended period of time
- due to the long curvature of the flask neck, no bacteria or spores were able to reach
the broth in the interior of the flask to trigger growth of new life after the lifedestroying heating procedure
- the outcome of this elegant experimental setup finally disproved the long upheld
spontaneous generation idea
“There is no spontaneous generation of life possible under the currently
existing life conditions and in our currently existing highly oxidative earth
atmosphere of today … “
5
SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCES
Intro Cell & Molecular Biology (BIOL 210); Instructor: Elmar Schmid, Ph.D.

in the llaattee 1199ttthhh cceennttuurryy, LLoouuiiss P
Paasstteeuurr and R
Ruuddoollff V
Viirrcchhoow
w concluded from their
observations and studies, that life arises only through reproduction of pre-existing life;
“life begets life”
- there is no spontaneous generation of new biological organisms possible under the
current Earth conditions
- generation of new life requires unique reproductive structures, e.g. spores, or a
special type of cells, i.e. generative cells, such as sperm and egg cells

in 11886611, the Russian chemist Butlerov succeeds to chemically synthesize the six
carbon-molecule glucose from inorganic precursors

Around 11990000, the Swedish scientist Svente Arrhenius (1859 – 1927) proposes and
advocates the hypothesis that life did not originate on Earth but was seeded from outer
space ( begin of the cosmic ancestry hypothesis)

in 11993388, the Russian biochemist A.I. Oparin and the British scientist J.B.S. Haldane
suggested that carbon-molecules that served as the basis of life were formed in an early
(primordial), oxygen-less (= anoxic) Earth atmosphere which consisted of methane,
ammonia, hydrogen, and water vapor  “Primordial Anoxic Earth Atmosphere
Theory”
- according to the core ideas of this theory, the early anoxic earth had a reducing
atmosphere which may have favored the spontaneous, reductive build-up (chemical
synthesis) of more complex molecules
- today, the modern earth atmosphere with its 21% oxygen content is a strongly
oxidizing environment which rather favors spontaneous oxidative chemical
processes

in 11995533, the American biochemist Stanley Miller tested this idea and showed for the
first time, that complex, organic compounds, such as amino acids, form spontaneously
under controlled lab conditions; the foundation of the “prebiotic broth theory” is laid
out
his famous “Miller-Urey apparatus” was a closed experimental system which
simulated the primordial composition of the oxygen-free atmosphere of the ancient
Earth (= primordial earth atmosphere), atmospheric discharges (lightning), volcanic
activity and considered the presence of an early ocean made of water (see Figure
below)
it contained methane, ammonia, water (vapor), and hydrogen which circulated
past a source of electric discharges
it resulted in the generation of amino acids (alpha-alanine, beta-alanine,
aspartic acid, alpha-amino-n-butyric acid, and several other unidentified amino
acids)
“The prebiotic broth theory is introduced into the origin of life discussions.”
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SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCES
Intro Cell & Molecular Biology (BIOL 210); Instructor: Elmar Schmid, Ph.D.
Simulation of the ancient Earth atmosphere and Earth
by Urey & Miller (1950s) in their famous Urey- Miller apparatus
 lead to the build-up of amino acids and other complex organic
molecules in their “pre-biotic soup”
Primordial
atmosphere
simulated
Electrical
discharges
CH4, H2
NH3
simulated
Lightning
yielded
Amino acids,
Organic molecules
H2O
simulated
Ancient
oceans
simulated
Volcanic activity/
Lava
-
different energy sources and proportions of gases used in the same experimental
setting even yielded purines, pyrimidines, and carbohydrates: all essential
building block molecules for life
7
SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCES
Intro Cell & Molecular Biology (BIOL 210); Instructor: Elmar Schmid, Ph.D.

in 11996600, Juan Oro’ experimentally obtains the biomolecule adenine after mixing
ammonia (NH3) and hydrocyanic gas with water and heating it to 194oC
adenine is the crucial precursor molecule for many important biomolecules, most
importantly ATP, DNA, RNA, FAD and NAD

in the 11997700ss, Sidney W. Fox demonstrates that amino acids, the building blocks of
proteins found in all living things, spontaneously organize themselves into cell-like
structures, so-called "protenoid microspheres” or proto-cells (see Figure below); he
showed the formation of organic polymers after dripping dilute aqueous solutions of
organic monomers on hot sand or clay
the proto-cells studied by S. Fox exhibited some of the features of living cells, such
as growth, membranous responses, metabolism and transfer of chemical
information
Spontaneous formation of Proto-cells
( Sidney Fox experiments)
Formation of free protocells on the surface of
abiotic thermal protein TP9
Protocell
Multi-protocells of thermal protein SIU-2
(diameters range from 0.3-0.6 μm)
8
SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCES
Intro Cell & Molecular Biology (BIOL 210); Instructor: Elmar Schmid, Ph.D.

in the 11998800ss, the American biochemist Tom Czech showed for the first time that certain
RNA molecules have enzymatic activity and work as so-called ribozymes (see Figure
below)
the idea was developed whereas early life-like processes, e.g. a primitive form of
metabolism, my have started in a so-called “RNA-world” with ribozymes as the
primordial enzymes on this planet
in modern living organisms today, catalytic RNAs or ribozymes still play a
significant role in many biological processes
ribozymes and catalytic active RNA molecules are known to be required:
1. for the viability of certain plant pathogens
2. for the “RNA business” of the human hepatitis delta virus (HDV)
 self-cleaving/RNA processing
3. as functional units of ribosomes (23S rRNA) for protein synthesis
4. as functional units of telomerases to protect the chromosomal ends
from “replicative erosion”
5. for gene self-splicing processes in the protozoan Tetrahymena
Five classes of ribozymes have been described of which the “hammerhead”
ribozyme is the best studied one (see detail A of Figure below)
Consensus structure (A) and turn-over cycle (B)
of a “hammerhead’ ribozyme
A

B
By the 11998800ss, many scientists consider protenoid microspheres with entrapped RNA
molecules as proto-cells and therefore the smallest unit of proto-life
9
SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCES
Intro Cell & Molecular Biology (BIOL 210); Instructor: Elmar Schmid, Ph.D.

in 11999922, Guenter Waechtershaeuser introduces the “Pressurized iron-sulfur world
theory” which suggests a deep ocean hydrothermal origin of a primitive autotrophic
metabolism of small carbon molecules, most importantly pyruvate and acetate, in a
deep ocean vent environment of earth crust iron sulfides and hot magmatic exhalations
(for an overview see Graphic below)
on the early, protein-less world, mineral-bound iron and nickel sulfides may have
had the function of inorganic catalysts of a primitive metabolic cycle
according to this theory, the inorganic iron and nickel sulfides surfaces of deep
ocean vent clefts may have served as early catalysts, before they were eventually
succeeded by the more effective protein-embedded minerals in form of cofactors of
enzymes
the mineral-bound iron and nickels sulfates may have mimicked the catalytic
activity of acetyl coenzyme A (CoA) synthase, an enormously important iron- and
nickel-containing enzyme complex present in modern chemoautotrophic organisms
 Literature: G. Waechtershaeuser, Science 289: 1307 – 1308 (2000)
Chemical reactions & End products in the Iron-Sulfur world cycle
 Primitive chemical cycle of the deep ocean vent environment?
CH3
C
CH3 – SH
CO2
O Acetic Acid
OH
Carbon dioxide
O
HO
CH3
Heat
CH3
OC
C
C
C
H2S
HCO2
CH3
CO
O
O
Methyl
thioacetate
S – CH3
O
C – C – CH3
Fe2+, Co, Ni2+
Mineral
Heat
library
CO
O
Carbon
O
C – C – CH3
NH3
Ammonia
Peptides
O
Graphic©E.Schmid/2004
 adopted with modifications
from G. Waechtershaeuser
O
HO
Pyruvic Acid
NH2
C – C – CH3
HO
Alanine
10
SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCES
Intro Cell & Molecular Biology (BIOL 210); Instructor: Elmar Schmid, Ph.D.

In 22000000, G. D. Cody et al. shows experimental evidence that the crucial cell metabolism
molecules pyruvic acid, acetic acid and alanine, form from formic acid in the
presence of carbon monoxide, nonylmercaptane and iron sulfilde at high pressures (0.2
-200 MPa) and temperatures (100 - 250oC) (see Graphic above)
he introduces the idea that important cell metabolism intermediates may have
formed through the reaction of alkyl sulfurs and carbon monoxide (CO) with iron
sulfide in ancient deep ocean hydrothermal vents (“cold smokers”)
he speculates that this chemistry may have provided the critical biomolecules for
early, primitive metabolic processes on the prebiotic earth
 Literature: George D. Cody, et al., Science 289: 1337 – 1340 (2000)
“The maxim of the prebiotic broth theory is “order out of chaos”. In contrast,
the iron-sulfur world experiments are serial, aimed at long reaction cascades
and catalytic feedback (metabolism) from the start. The maxim of the ironsulfur world theory should therefore be “order out of order out of order”
G. Waechtershaeuser

in 22000033, C. Huber & G. Waechtershaeuser (Technical University Munich, Garching,
Germany) showed proof for a primitive peptide cycle with the amino acid
phenylalanine under test tube conditions which may have occurred on the primordial
world, e.g. in certain deep ocean environments (“black smokers”)
the observed peptide cycle had anabolic and catabolic segments resembling a
modern metabolic cycle operating in living organisms
they showed carbon monoxide (CO)-driven build-up of short peptides from α-amino
acids under hot aqueous test tube conditions in the presence of colloidal iron-nickel
sulfide [ (Fe,Ni)S ] minerals
they also reported the CO- and (Fe,Ni)S ] mineral-dependent degradation
(hydrolysis) of a dipeptide (L-Phe- L-Phe) down to amino acid monomers
Literature: C. Huber, et al., Science 301: 938 – 940 (2003)

in 22000044, the NASA scientist Jason Dworkin (Goddard Space Flight Center, Maryland),
introduces the idea that early biological membranes might have been formed inside
dense interstellar clouds and may have been seeded on earth via impacting asteroids
his idea his based on the experimental results he received with lab-simulated
space dust he mixed with water, methanol, ammonia, carbon monoxide in the
extreme cold (- 258 oC) under the influence of strong UV irradiation
under these experimental set-up conditions he found organic membranes that selfassembled into hollow, spherical structures

Even though our modern scientific understanding of one of the greatest mysteries in the
universe, the origin of life, is far from being understood, today, the scientific community
favors 3 major theories how life may have started out and evolved on our planet
11
SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCES
Intro Cell & Molecular Biology (BIOL 210); Instructor: Elmar Schmid, Ph.D.
1.
Prebiotic broth theory & Organic chemical evolution theory

The core idea of the prebiotic broth theory is that life slowly originated from inorganic
matter in a prebiotic broth under the influence of natural physico-chemical forces either
on earth of out there in the universe; according to this theory, carbon-based molecules
(once formed through physico-chemical forces) created a molecule-enriched prebiotic
broth in which self-assembly eventually formed self-sustaining and stable high
molecular weight carbon-structures, such as RNA, proteins and lipids through a rigorous
“sorting out mechanism” ( selective pressure & chemical evolution)

The core idea of the organic chemical evolution theory assumes that the early life
forms evolved by macromolecular build-up from simple carbon precursor molecules by
chemical synthesis processes; according to this theory macromolecules assembled
spontaneously and evolved in a totally different earth atmosphere than the one we know
today and which we breathe; the theory (which is associated with the scientists M.
Eigen & L. Orgel) is strongly based on scientific evidence supporting an oxygen-free,
ancient, so-called anoxic primordial earth atmosphere (for an overview see table
below) and also includes key ideas of the evolutionary theory, such as natural selection
and selective pressure
Scientific evidence strongly suggests that the early earth atmosphere existed
mainly of hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2), nitrogen
gas (N2), methane (CH4), ammonium (NH3) and water vapor
Gas composition of the different atmospheres in Earth’ history

Chemical Composition of the Earth’ atmosphere today:
Nitrogen (N2)
78%
Oxygen (O2)
21%
Carbon dioxide (CO2)
0.03 %
other miscellaneous gases, e.g. H2O

the ancient, primordial Earth atmosphere was most likely composed of:
Hydrogen (H2) and
Helium (He)
these two gases are relatively rare on Earth today compared to other places
in the universe
they were probably lost to space early in Earth's history

the second atmosphere establishing on Earth was primarily produced by volcanic
outgasing and most likely consisted of:
Water (H2O)
Carbon dioxide (CO2)
Sulfuroxide (SO2)
Carbon monoxide (CO)
Sulfur (S2)
Nitrogen (N2)
Hydrogen (H2)
Ammonia (NH3) and
Methane (CH4)
12
SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCES
Intro Cell & Molecular Biology (BIOL 210); Instructor: Elmar Schmid, Ph.D.
 this atmosphere most likely contained no free oxygen (O2) at this time, since it is
not traceable in gases of modern volcanoes
 traces of existing oxygen may have been quickly reduced by transition metals
as part of the earth crust, such as iron (Fe2+  Fe3+)

the chemically reducing (= oxygen-free) earth atmosphere, rather than oxidizing
atmosphere favored anabolic (= chemical build-up) reactions and the formation and
accumulation of small organic molecules, e.g. amino acids and even more complex
polymers
in his famous ‘pre-biotic soup’ experiment in the 1950s, S. Miller confirmed the
formation of organic molecules under conditions where he simulated the early earth
atmosphere conditions in his lab
electrical sparks (which simulated atmospheric lightning) triggered the formation of
amino acids, nucleotides and other bio-molecules in an atmosphere consisting of
water vapor, CH4, NH3 and molecular hydrogen
the amount of free O2 in the atmosphere gradually rose from 1 - 10 % during the
Proterozoic era due to the activity of photoautotrophic organisms, most importantly
the photosynthesizing cyanobacteria and purple bacteria

scientists favoring the chemical evolution theory assume that the polymers of life (RNA,
peptides) were formed by so-called dehydration synthesis on hot rock or clay
formations originating from volcanic activities
these regularly flooded clay and rock formations may have served as the first
polymerization sites
these first genes in form of short strands of RNA laid the basis for reproduction; the
most important hallmark of life

the first strands of RNA assembled with complementary RNA molecules in the prebionic atmosphere without the assistance of protein structures, but probably with the
(catalytic) help of the net charges of transition metals being part of clay or rock surfaces
the first rounds of replication occurred
these simple replication/assembly processes may have been aided by specially
formed and catalytically active RNA molecules, called ribozymes
today we now that ribozymes can catalyze RNA splicing and polymerization
more recently scientists discovered that the polypeptide-forming cellular complex
called ribosome is actually a ribozyme!
in the pre-bionic so-called RNA world, RNA build the first genes long before DNA
took over this important functional part of life

scientists assume that early forms of so-called molecular cooperation must have
occurred in chemically unique micro-environments, e.g. electrically charged clay
surfaces/cavities on our young planet
the first polypeptide chains arose on self-replicating RNA polymers/ribozymes
some of these generated polypeptide chains started to act as primitive enzymes
and protective/stabilizing proteins
the first primitive RNA polymerase may have evolved and started to aid the RNA
replication process
13
SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCES
Intro Cell & Molecular Biology (BIOL 210); Instructor: Elmar Schmid, Ph.D.

spherical membranes made from hydrated (= flooded) lipid molecules started to enclose
the RNA-polypeptide cooperations may have formed the first simple cell-like structures
or so-called proto cells

after millions of years of repeated rounds of trial and error and millions of probed
molecular cooperations and combinations the first efficient, self-replicating prokaryote
evolved on our planet
Summary of the prebiotic broth & Organic chemical evolution theory
1. Formation of complex organic molecules, such as amino acids, nucleotides,
occurs from simple precursor molecules, e.g. CO, H2, N2 in an early, oxygen-free
Earth atmosphere and accumulate to form a prebiotic broth
2. Formation of the first complex polymers, e.g. nucleic acids, polypeptides, from
organic monomers by dehydration synthesis in hot springs on charged surfaces,
such as metal-containing rocks or clay formations
3. Establishment of the first primitive metabolic cycles on iron-nickel sulfides
minerals
4. RNA established itself as the first self-replicating genetic material; in this “RNA
world”, short strands of RNA copy themself accelerated with the help of
Ribozymes
5. The first molecular cooperations (“coops”) form between many polymers and
many other complex organic molecules
6. the first “useful” polypeptide chains show enzyme activity and trigger the
evolution of reciprocal molecular cooperation between nucleic acids and
proteins; RNA/protein coops form
7. formation of coops between self-replicating RNA/protein complexes and
microscopic spheres enter the scene; so-called micelles made of early
phospholipids create the first pre-biotic “cells” (= chambers)
8. Ongoing molecular evolution creates the first membrane-surrounded and selfreplicating primitive proto cells
14
SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCES
Intro Cell & Molecular Biology (BIOL 210); Instructor: Elmar Schmid, Ph.D.
2.
The pressurized iron-sulfur world theory
 this theory suggests a fast origin of life via a primitive autotrophic metabolism of small
carbon-based molecules, such as pyruvic acid, acetic acid and alanine, in the hot and
high pressure environment of deep ocean vents with the catalytic help of iron-nickel
sulfur mineral surfaces (see section above)
this idea is supported by a series of lab experimental evidence (see Corvis &
Waechtershaeuser in the sections above) and the interesting observation that
transition metal (e.g. nickel, iron, cobalt) sulfide clusters play a crucial role for the
catalytic activity of many metabolically important enzymes in diverse groups of
biological organisms
also, iron-nickel-containing mineral sulfides are very common in deep ocean
hydrothermal and volcanic vents
3.
The panspermia (or cosmic ancestry) theory

this theory favors the idea that life originated out in space and was carried to Earth in
form of “seeds”/”endospores” traveling on/inside a meteorite; a meteorite impact
early in Earth history may have triggered (“seeded”) the evolution of life

this idea which recently gained increased popularity in the scientific community is
supported by the discovery of extraterrestrial (ET) organic compounds in meteorites
1. the so-called Allende Meteorite, a meteorite which landed in 1969 near Allende,
Mexico, was found to contain amino acids in its structure
2. a meteorite believed to be from Mars, discovered in 1996 in Antartica, shows
several ET life-supporting features:
it contains hydrocarbon molecules (the same as breakdown products of
dead micro-organisms on Earth)
its mineral phases are consistent with by-products of bacterial activity
it shows tiny carbonate globules which may be microfossils of the primitive
bacteria

these findings also re-fueled the discussion about the possible existence of life
elsewhere in the Solar System and the universe

it also created further interest in the newly inaugurated biological sub-discipline of
Astrobiology

Future studies and discoveries will have to bring final proof which of the introduced
theories turns out to be correct and best describes the currently enigmatic scenario
which led to the development of life on our planet

despite of the (currently) fragmented knowledge of the origin of life on our planet and
the controversial discussions regarding the evolution of life, the earliest, traceable
organisms evidently lived in form of primitive prokaryotes in the early oceans
evidence of the first fossilized prokaryotes can be found in form of unique
Precambrian rock formations called stromatolites, some of which have been dated
back to more than 3 billion years
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SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCES
Intro Cell & Molecular Biology (BIOL 210); Instructor: Elmar Schmid, Ph.D.

between 3.5 and 2.5 billion years, prokaryotes diversified already and appear in
different shapes and forms in geological formations

due to the metabolic activity of the photosynthesis-active cyanobacteria, the
concentration of molecular oxygen (O2) increases in the Earth’s atmosphere
this “first mass pollution” of the atmosphere in earth history led to a radical change
in the bio-diversity on planet earth
the increased oxygen concentration in the air triggered the mass extinction of
anaerobic forms of life
Under this slow but steady selective pressure and as a consequence, new,
oxygen-adapted forms of life arise

about 1.7 billion years ago the first ‘respirating’ eukaryotic cells appear on Earth and
start their victorious evolution

between 600 and 500 million years ago during the Cambrian period (590 – 505 mya),
the first, primitive but structurally distinctive multi-cellular organisms appear which
leave their traces in fossil records (see Images below)
the first animal-like fossils appear at the end of the Proterozoic age (650 – 544
mya), also known as the Vendian period
the first diversification of soft-bodied organisms, such as Dickinsonia, Tribrachidium
and Leanchoilia illecebrosus, collectively known as the “Vendian fauna” or
“Ediacaran fauna“ falls into this time period
in many cases, scientists are not sure whether these ancient life forms were algae,
lichens, giant protozoans, or even a separate kingdom of life
Life form of the Cambrian period (590 – 505 million years ago)
Leanchoilia
illecebrosus
16
SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCES
Intro Cell & Molecular Biology (BIOL 210); Instructor: Elmar Schmid, Ph.D.
Life forms of the Cambrian period (590 – 505 million years ago)
Image of fossil record
Name
Dickinsonia
- Phylum ??
Tribrachidium
- Cnidarian?
- Echinoderm?

about 500 – 400 million years ago the first primitive plants enter the scene in form of
colonial green algae

As mentioned at the very beginning of this chapter, today, more than 2 million different
life forms or species call this planet home and testify the great success story of the
great phenomenon called life

Biologists classified these life forms into three major domains which include the
Eubacteria (monerans), the Archaea bacteria and the Eukaryotes (see Graphic below)
and seven kingdoms of life

According to a very recently published findings, which are based on a bio-informaticsbased complete genome (DNA) analysis of selected prokaryotic and eukaryotic
genomes, some scientists introduce the idea of a “ring of life” rather than to continue
to speak of a tree of life with individual unconnected branches
17
SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCES
Intro Cell & Molecular Biology (BIOL 210); Instructor: Elmar Schmid, Ph.D.
-
-
this new model showing the different major domains of life arranged in a connected
ring considers the widely observed genetic phenomenon of horizontal gene
transfer (“gene grapping”) amongst different species
the ring includes following six major domains of life:
1.
2.
3.
4.
5.
6.
Bacilli (Eubacteria)
Cyanobacteria
Proteobacteria
Archaea bacteria
Eocyta
Eukaryota
The 3 major domains of life on Earth
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