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How To Study The Origin of Life On Earth

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Title: How To Study The Origin of Life On Earth


1
Astrobiology The Origins of Life Monday, January
29, 2007
2
Origins of Life
  • today, we know of only one form of life life on
    Earth, all of which shares a common origin and
    uses DNA molecules as a fundamental means of
    reproducing itself
  • understanding how life originated on Earth may
    provide us with clues as to how life might
    originate elsewhere in the universe and how we
    might recognize it

3
Searching for Evidence of Early Life
  • there are two direct ways of searching for
    evidence of the existence of life during the
    earliest part of Earth history
  • using light and electron microscopy (SEM, ESEM,
    TEM) and most recently AFM to search for
    fossilized microbes
  • geochemical measurement, in rocks that are
    interpreted as metasediments, of putative organic
    traces in the geochemistry. These traces include
    clumps of carbon, which may or may not be
    biogenic, and biological isotopic fractionation,
    both of light elements such as C, N, S, O and D/H
    that make up the cell mass, and of the metals
    that constitute key housekeeping proteins (Fe,
    Cu, Zn). The geochemical approach also involves
    micro-scale in-situ analyses of isolated
    microfossils from shale and chert samples.

4
When Did Life Start on Earth?
  • the best estimate of the origin of the universe
    is 13.7 Ga
  • earliest possible emergence of life in the
    universe is 12.7 Ga
  • age of the Earth is 4.55 Ga
  • if the assumption that the Hadean period was
    relatively cool is correct, then from 4.4-4.3 Ga,
    the conditions for prebiotic chemistry and
    appearance for life were already met, i.e.,
    liquid water, continental crust, etc.
  • however, the Late Heavy (Meteoritic) Bombardment
    between 4.0 and 3.8 Ga likely sterilized the Earth

5
Isua Supracrustal Belt
  • the oldest known sedimentary rocks are from West
    Greenland (Isua Supracrustal Belt) and dated as
    no younger than 3.85 Ga (likely older) and
    include banded iron formation beds, metacherts,
    pillow lava structures, carbonates, and felsic
    metasediments

The world's oldest rocks may they contain the
earliest evidence for life on Earth. These rocks
are found in southwest Greenland, including Iron
Mountain of the Isua region.
6
Isua Supracrustal Belt
  • researchers have studied tiny graphite grains
    embedded in different rocks found in the Isua
    formations
  • by measuring the ratio of carbon isotopes, these
    researchers determined that the graphite
    contained carbon of biological origin
  • two common and stable isotopes of carbon, 12C and
    13C, occur in a mixture in the Earths atmosphere
  • biological processes build organic molecules with
    a higher carbon 1213 d13C ratio than abiotic
    processes

7
Isua Supracrustal Belt
  • and because both isotopes are stable, the ratio
    remains in all of lifes products, even after
    billions of years
  • this interpretation, however, remains
    controversial as processes such as metamorphism
    can change the original carbon isotope ratio
    (isotope exchange with carbonates or CO2-rich
    fluids and devolatilization reactions)

8
BIF, Akilia Island, West Greenland
  • the highly metamorphosed quartz-pyroxene rock on
    the SW tip of Akilia Island are dated at 3.8 Ga
    and has for long been the center of attention
    regarding the oldest traces of life on Earth
  • the BIF was found to contain graphite inclusions
    within apatite crystals

9
BIF, Akilia Island, West Greenland
  • the low d13C of these graphite inclusions
    suggested a biologic source material that had
    retained its original carbon isotope signature
  • it has been argued, however, that the protolith
    of this rock was not a BIF, but instead a highly
    metasomatized ultramafic rock, which does not
    represent a marine depositional setting and
    would, therefore, not be able to harbour traces
    of ancient life
  • the age of the rock has also been challenged and
    that the apatite crystals are much younger than
    the surrounding rock matrix

10
Apex Chert - Pilbara, Western Australia
  • microfossils from the Apex Chert, North Pole,
    Australia
  • these organisms are Archean in age, approximately
    3.465 Ga, and resemble filamentous cyanobacteria
  • the first appearance of cyanobacteria in the
    fossil record is a matter of great scientific
    interest because they gave rise to the
    oxygen-rich atmosphere that allowed the evolution
    of higher life forms

11
Apex Chert - Pilbara, Western Australia
  • researchers have recently suggested, however,
    that these are pseudofossils (artefacts) formed
    when carbonaceous glass associated with one of
    Earths oldest hot springs recrystallized into
    spherulitic silica (abiotic processes associated
    with hydrothermal activity)

12
Hamersley Range, West Australia
  • the oldest unambiguous fossil evidence for
    cyanobacteria is found in 2.15 Ga rocks of the
    Belcher Supergroup, Canada, but biomarkers, which
    are complex hydrocarbons (molecular fossils) that
    are derived from once living organisms, suggest
    the presence of cyanobacteria, methanotrophs or
    methylotrophs, and Eucarya in 2.77 Ga rocks of
    the Hamersley Basin, Australia.

Silicified microbial mats, Belcher Supergroup
13
Indirect evidence for the activity of
methanogenic Archaea derived from global carbon
isotopic anomalies in the kerogen of 2.8 to 2.5
Ga sedimentary rocks. Biomarker evidence
(2a-methylhopanes) for cyanobacteria. Oldest
known fossils with diagnostic cyanobacterial
morphology from the 2.15-Ga Belcher Supergroup,
Canada, Biomarker evidence (diverse steranes) for
Eucarya. Oldest known fossils with possible
eukaryotic morphology from the 1.87-Ga Negaunee
Iron Formation, Michigan. Previous oldest
sterane biomarkers from the 1.64-Ga Barney Creek
Formation, McArthur Basin, Northern Territory.
Oldest known eukaryotic fossils assigned with
confidence to an extant phylum (Rhodophyta) from
the 1.26 to 0.95 Ga Hunting Formation, Somerset
Island, Canada. Sulfur-isotopic evidence for
mesophilic sulfate-reducing Bacteria from North
Pole, Pilbara Craton, Western Australia.
14
When Did Life Start on Earth?
  • if life originated on Earth, it did so in a
    window of at most 1 Ga (4.55 Ga to 3.5 Ga), most
    plausibly 400 Ma (3.9 Ga to 3.5 Ga), and possibly
    lt100 Ma (3.9 Ga to 3.85 Ga), if the Greenland
    (3.85 Ga) carbon isotopic signal is correct
  • if life originated elsewhere, the window expands
    to 12 to 9 Ga
  • that full length of time might not be available
    on a single planet, but the Earth has provided a
    life-friendly environment for at least 3.5 Ga

15
Origin of Life
  • no consensus for a theory or model of precellular
    life
  • theories of the origin of life fall into two
    categories
  • extraterrestrial origin
  • terrestrial origin

16
Models for the Origin of Life
17
History of the Origins of Life
  • abiogenesis is the generation of complex life
    from non-living matter
  • earlier notions of abiogenesis, i.e., autogenesis
    or spontaneous generation (or "Aristotelian
    abiogenesis"), held that living organisms are
    generated by decaying organic substances, e.g.,
    mice spontaneously appear in stored grain or
    maggots spontaneously appear in meat

18
History of the Origins of Life
  • in the 1800s, chemist Louis Pasteur developed the
    "germ theory of medicine and argued that people
    became ill because they were infected by
    invisible things in the surrounding environment
    called germs which were not acceptable to
    most medical experts of the early 1800s

19
Modern Abiogenesis
  • in 1871, Charles Darwin made the suggestion that
    life may have begun in a "warm little pond, with
    all sorts of ammonia and phosphoric salts, light,
    heat, electricity, etc. present, that a protein
    compound was chemically formed ready to undergo
    still more complex changes, at the present day
    such matter would be instantly devoured or
    absorbed, which would not have been the case
    before living creatures were found."
  • thus, when Earth was ripe for life, the basic
    compounds necessary for metabolism might have
    existed in surplus with no competition from oxygen

20
Modern Abiogenesis
  • the modern definition of abiogenesis is concerned
    with the formation of the earliest forms of life
    on Earth from primordial chemicals, in an
    environment regarded as similar to that at the
    time shortly after the formation of the Earth

21
Current Models of the Origins of Life
  • most currently accepted models build in one way
    or another upon a number of discoveries
    concerning the origin of molecular and cellular
    components for life

22
Five Steps to the Origins of Life
  • plausible pre-biotic conditions result in the
    creation of certain basic small molecules
    (monomers) of life, such as amino acids.
  • demonstrated in the Urey-Miller experiment by
    Stanley Miller and Harold Urey in 1953
  • phospholipids (of an appropriate length) can
    spontaneously form lipid bilayers, one of the two
    basic components of a cell membrane
  • the polymerization of nucleotides into random RNA
    molecules might have resulted in self-replicating
    ribozymes (RNA world hypothesis)

23
  • selection pressures for catalytic efficiency and
    diversity result in ribozymes that catalyse
    peptidyl transfer (hence formation of small
    proteins), since oligopeptides complex with RNA
    to form better catalysts - thus the first
    ribosome is born, and protein synthesis becomes
    more prevalent
  • proteins outcompete ribozymes in catalytic
    ability, and therefore become the dominant
    biopolymer - nucleic acids are restricted to
    predominantly genomic use

24
Origin of Organic Molecules
We must always recognize that there were both
endogenic and exogenic sources of organic
materials.
25
Exogenic Origin of Organic Molecules
  • the origin of life in Universe was influenced by
    organic compounds from space or even a product of
    organics present in the nebula
  • these organic molecules have been detected in
    comets, meteorites, and interplanetary dust
    particles (IDPs)
  • much of the infalling material during the era of
    bombardment consisted on comets, which contained
    not only water but CH4, NH4, methyl alcohol,
    hydrogen cynanide and formaldehyde
  • these molecules along with CO and CO2 provide the
    raw materials in building complex organic
    molecules

26
Red Giant CRL 2688
  • A.K.A., the Egg Nebula, this Red Giant 3,000
    light-years from us is ejecting material out into
    space in cloud of dust and gas moving out from
    the star, at 20 km/s
  • this material is where we encounter our first
    organic molecules

27
Nebular Chemistry
Nothing survives
Reactions on surfaces (Fischer-Tropsch)
Interstellar ice is stable
28
there is a class of molecules that has been found
in meteorites. . .
. . . in fact, you might even know what they
taste like...
29
Polycyclic Aromatic Hydrocarbons (PAHs)
  • PAHs are stable, complex netwoks of benzene
    rings made mostly of carbon, and are everywhere
  • these sooty molecules may take up 10-15 of all
    the galactic carbon!
  • they are also carcinogens

30
Dense Interstellar Clouds
  • dusty cold and dark in these clouds the average
    temperature is 10 K (-263 C) and nearly
    everything freezes out onto microscopic grains
    forming ice mantles
  • UV radiation and cosmic rays bombard the ice,
    breaking bonds

radiation
CH3OH
PAH
H2O
CO
CO2
more complex organic molecules
31
  • in January 2004, a team led by A. Witt discovered
    the spectral signatures of the polycyclic
    aromatic hydrocarbons anthracene and pyrene in
    the UV light emitted by the Red Rectangle nebula
    - potentially vital organic molecules for the
    formation of life

32
  • laboratory simulation of PAHs in cometary ice
    analogs showed that during irradiation of comets
    by a young star, biogenic types of PAHs could be
    formed such as quinines
  • quinones are found in all living organisms on
    Earth and thus a part from being the largest
    fraction of carbonaceous matter in the universe,
    PAH molecules might be important for early life

33
Polycyclic Aromatic Hydrocarbons (PAHs)
34
Endogenesis Organic Synthesis by Other Energy
Sources
  • organic synthesis initiated by impact shock
  • Miller-Urey, Uro and Sagan Experiments
  • polymerization
  • Iron-Sulphur World

35
Organic Synthesis by Impact Shock
  • laboratory experiments have shown that in
    strongly reducing atmospheres, shock waves
    emanating from meteoroids either traversing the
    Earths atmosphere or during impacts can produce
    large quantities of organics
  • shock heating of reducing gas mixtures can
    produce amino acids
  • however, in the apparently more likely case of a
    mildly reducing or intermediate oxidizing
    atmosphere, atmospheric shocks were probably of
    little importance for direct organic production

36
Miller Urey Experiments
  • in 1953, Stanley Miller designed an experimental
    test for Darwins conception of the origin of
    life in ponds or tide pools
  • the experiment used a highly reduced mixture of
    gases (methane, ammonia, hydrogen and oxygen),
    which was at that time considered to be the
    composition of the prebiotic atmosphere
  • other less reducing gases produce a lower yield
    and variety
  • Miller discharged an electric spark into a
    mixture thought to resemble the primordial
    composition of the atmosphere

37
Miller Urey Experiments
  • a mixture of CH4, NH3, H2O, and H2, thought to
    represent Earths prebiotic atmosphere, was
    circulated through a liquid water solution and
    continuously sparked by an electrical discharge
    as an energy source
  • chemical analysis of the liquid pool revealed the
    formation of organic molecules including several
    amino acids, which are the building blocks of
    life, and fatty acids from inorganic components

38
Miller Urey Experiments
  • the simple inorganic molecules that Miller placed
    into his apparatus, produced a variety of complex
    molecules
  • the interactions of these molecules would have
    increased as their concentrations increased and
    reactions would have led to the building of
    larger, more complex molecules

39
Miller Urey Experiments
  • subsequent experiments substituted ultraviolet
    light or heat as the energy source or have
    altered the initial abundances of gases - in all
    experiments representatives or precursors of all
    four organic macromolecular classes amino acids
    formed
  • Miller's (and subsequent) experiments have not
    proven life originated in this way, only that
    conditions thought to have existed over 3 Ga were
    such that the spontaneous (inorganic) formation
    of organic macromolecules could have taken place
  • simple organic molecules are a long way from a
    fully functional self-replicating life form
    however, in an environment with no pre-existing
    life these molecules may have accumulated and
    provided a rich environment for chemical
    evolution ("soup theory")

40
Endogenesis
  • while there is still debate on the generality of
    the experimental synthetic pathways and on the
    stability of the molecules produced most if not
    all of the essential building blocks of proteins,
    carbohydrates, and nucleic acids can be readily
    produced under quite general primitive reducing
    conditions
  • while such experiments have not led to the
    synthesis of living things from the basic
    materials of the early Earth, they do give
    biologists more reasons to believe that the
    chemical steps that led to life are not as
    difficult to reproduce as was once thought

41
Iron-Sulphur World Theory
  • is a hypothesis for the origin of life advanced
    by Günter Wächtershäuser involving forms of iron
    and sulfur
  • Wächtershäuser claims that an early form of
    metabolism predated genetics, i.e., chemical
    reactions that produce energy in a form that can
    be harnessed by other processes
  • once a primitive metabolic cycle was established,
    it began to produce ever more complex compounds

42
Iron-Sulphur World Theory
  • key idea of the theory is that this early
    chemistry of life occurred not in bulk solution
    in the oceans, but on mineral surfaces (e.g. iron
    pyrites) near deep submarine vents
  • carbon-rich molecules could accumulate on iron
    pyrite crystals and acquire new carbon atoms from
    material ejected by the hydrothermal vents
  • the first 'cells' would have been lipid bubbles
    on the mineral surfaces

43

Pyrite as a Source of Energy and Molecular Order
Polymerization Reaction Adsorption of
glyceraldehyde-3- phosphate to the surface of
pyrite followed by polymerization (Wachterhauser
1988)
44
Formation of Pyrite
  • CO2 H2 ? HCOOH ?Go 30.2 kJ/mol
  • Fe2 2H2S ? FeS2 4H 2e-
  • FeS H2S ? FeS2 H2 ?Go -41.9 kJ/mol
  • Fe CO3 H2S (aq) ? FeS2 2H2 H2O CO2 ?Go
    -61.7 kJ/mol
  • CO2 FeS H2S (aq) ? FeS2 H2O HCOOH ?Go
    -11.7 kJ/mol
  • Formation of pyrite can serve as a source of
    reducing power.

45
Iron-Sulphur World Theory
  • however, like those who hypothesize that life
    began in ponds or tide pools, Wächtershäuser has
    no clear way to pass from the building blocks to
    living creatures
  • nevertheless, with his emphasis on the high
    temperature origin of life, he may be on the
    right track

46
From Organic Molecules to Protocells
  • there are many different hypotheses regarding the
    path from organic molecules to protocells
  • virtually all biologists now agree that bacterial
    cells cannot form from nonliving chemicals in one
    step - if life arises from nonliving chemicals,
    there must be intermediate forms, "precellular
    life
  • three basic approaches
  • genes-first - the early appearance of nucleic
    acids
  • metabolism-first - the evolution of biochemical
    reactions and pathways
  • hybrid models - combine aspects of both

47
The Beginnings of Life on Earth
The only premise that all precellular theories
share is that it would be an extremely long time
before the first bacterial cells evolved
How long would it take?
ratio of actual useful proteins to possible
random proteins up to one in something like
10500, barring incredible luck, something like
10500 trials to probably find one
48
"Genes First" Models RNA World
  • the RNA world hypothesis proposes that RNA was
    actually the first life-form on Earth, later
    developing a cell membrane around it and becoming
    the first prokaryotic cell
  • hypothesis is supported by the RNA's ability to
    store, transmit, and duplicate genetic
    information, just like DNA does
  • RNA can also act as a ribozyme (an enzyme made of
    ribonucleic acid)
  • because it can reproduce on its own, performing
    the tasks of both DNA and proteins (enzymes), RNA
    is believed to have once been capable of
    independent life

49
Metabolism First Models
  • several models reject the idea of the
    self-replication of a "naked-gene" and postulate
    the emergence of a primitive metabolism that
    could provide an environment for the later
    emergence of RNA replication
  • in 1924, Alexander Oparin suggested the idea of
    primitive self-replicating vesicles - basic
    organic chemicals might form into microscopic
    localized systems (e.g., coacervates) - possible
    precursors of cells - from which primitive living
    things could develop
  • more recent variants in the 1980s and 1990s
    include Günter Wächtershäuser's iron-sulfur world
    theory and models introduced by Christian de Duve
    based on the chemistry of thioesters (compounds
    resulting from the bonding of sulfur with an acyl
    group an alkyl group attached to a carbon-oxygen
    double bond)
  • however, the idea that a closed metabolic cycle,
    such as the reductive citric acid cycle proposed
    by Günter Wächtershäuser, could form
    spontaneously remains unsupported

50
Aerosols as Prebiotic Chemical Reactors
  • aerosol sizes with significant atmospheric
    lifetimes are the same as those of single-celled
    organisms
  • aerosols that are coated with organic surfactant
    layers may act as a chemical reactor in the
    prebiotic production of polymeric molecular
    species

(Dobson et al. 2000)
51
Clay Minerals and the Origin of Life
  • clay minerals have a very complex crystalline
    structure, with a complex pattern of positive and
    negative charges
  • clay minerals can grow, adding new atoms while
    maintaining its crystal structure (Genetic
    Takeover)
  • it has been shown experimentally that clay
    minerals can catalyze the formation of at least
    small amino acids and nucleotide polymers

52
Genetic Takeover and the Mineral Origins of Life
  • Genetic Takeover
  • the original replicator (i.e., life) probably was
    not DNA possibly a primitive genetic system such
    as clay minerals or crystal medium, which RNA
    replaced
  • a mechanism by which evolution may produce
    changes in the genetic substrate of organisms

53
Genetic Takeover
  • the yellow regions represent phenotypes - G1 is
    the primary genetic substrate, and G2 is the
    secondary one. Arrows within organisms indicate
    paths of genetic expression
  • a simple organism with genetic substrate G1
    produces substance G2 as a component of its
    metabolic processes
  • G2 is inherited - and comes to carry heritable
    information. Gradually, G2 displaces G1 as the
    primary genetic material for the organism
  • secondary genetic material arises not as a
    modification of the primary one, but rather from
    molecules synthesized under its control

54
Clay Minerals and Genetic Takeover
  • CairnsSmith (1982) proposed that clay minerals
    were lifes ultimate ancestor
  • characteristics of clay minerals
  • products of processes of weathering and
    diagenesis
  • main component of soils and sediments
  • extensive structural variation
  • high affinity for adsorption of H2O and organics
  • high ion exchange capacity
  • clay minerals could provide the basis for an
    evolution through natural selection

55
  • the tetrahedral layer consists of a 2D network of
    corner linked tetrahedras the cation is mostly
    Si, with some Al-substitution - the interlayer
    space is filled by cations such as K, Na, Ca, and
    Mg - the octahedral layer consists of a 2D
    network of edge-linked octahedras the octahedral
    cation is predominantly Al, Fe, Cr, and Mg

Smectite
i t o t
Illite
i t o t
56
Replication of Clay Crystals
Zone A Clay crystals are impervious, deflecting
the flow of nutrients. Zone B Clay crystals
do not adhere and are washed out of
system. Zone C Some clay crystals stick to the
walls but let nutrient solutions flow.
57
Polymerization of Organic Molecules onMineral
Surfaces
  • it is difficult if not impossible to synthesize
    long polymers of amino acids, nucleotides, etc.,
    in homogeneous aqueous solutions
  • minerals with ion-exchange properties (e.g., clay
    minerals), however, may have functioned in the
    prebiotic synthesis of negatively-charged
    polymers
  • the lattice structure of clay minerals such as
    kaolinite may acts as templates for the
    organization of organic matter into polymers
  • polymers are long-chain molecules composed of
    many similar or identical molecular subunits,
    e.g., starch

58
Structural relationship between kaolinite-amino
acid-peptide system
59
(No Transcript)
60
Clay Minerals and Origins of Life
  • it is likely that if clays or like minerals
    played a role in the origin of life, aluminum and
    silicate would be more widely distributed in
    biology - instead, these compounds are rare

61
Deep-Hot Biosphere Model
  • deep subsurface offers infinite possibilities for
    the mixing of water with various chemical and
    physical conditions
  • life in subsurface environments is protected
    towards meteoritic impacts, ultraviolet
    irradiation, volcanic eruptions and desiccation
    and is rich in surfaces with
  • the oxygen-poor water reacts with iron-bearing
    minerals such as olivine and pyroxene to make H2
  • bacteria use the H2 and dissolved CO2 to make CH4
    and other hydrocarbon molecules needed to build
    cell material

62
Deep Basins
Life on our planet may have evolved first at
depth, then migrated to the surface as the
environment became more tolerable.
63
Cold Environments
  • organic compounds such as aminoacids have finite
    lifetimes in solution,and their stability
    decreases markedlyas the temperature increases
  • at the highest temperatures associated with
    hydrothermal vents,amino acids cannot survive at
    all
  • a global ice cover and colder temperatures would
    afford significant protection against thermal
    degradation
  • a concentrated mixture of solutes available
    during thaws could undergo a burst of chemical
    reactions leading to more complex molecules, a
    few of which could be on the evolutionary pathway
    to life.

64
Hydrothermal Vents
  • the first cellular life forms may have evolved
    inside so-called black smokers at seafloor
    spreading zones in the deep sea
  • many of the basic components of
    biochemical/biological systems reflect ancestry
    in a hydrothermal system, including metal
    proteins, especially those involving
    ironsulphur, nickel, molybdenum, copper, cobalt
    and zinc, some of which, such as metal-nitrogen
    structures
  • hydrothermal vents systems would have allowed
    sulphate reducers to exploit the oxidation
    contrast between the atmosphere-ocean system,
    open at the top to space, and the more reduced
    fluids in contact with mantle derived magma

65
A. On land, around a volcano
B. On seafloor, a mid-ocean ridge
66
Hydrothermal Vents
  • the micro-caverns provide a means of
    concentrating newly synthesised molecules,
    thereby increasing the chance of forming
    oligomers
  • the steep temperature gradients inside a black
    smoker allow for establishing "optimum zones" of
    partial reactions in different regions of the
    black smoker (e.g. monomer synthesis in the
    hotter, oligomerisation in the colder parts)
  • the flow of hydrothermal water through the
    structure provides a constant source of building
    blocks and energy (freshly precipitated metal
    sulfides)

67
Hydrothermal Vents
  • the model allows for a succession of different
    steps of cellular evolution (prebiotic chemistry,
    monomer and oligomer synthesis, peptide and
    protein synthesis, RNA world, ribonucleoprotein
    assembly and DNA world) in a single structure,
    facilitating exchange between all developmental
    stages
  • synthesis of lipids as a means of "closing" the
    cells against the environment is not necessary,
    until basically all cellular functions are
    developed - the synthesis of a lipid membrane
    would allow the organisms to leave the
    microcavern system of the black smokers and start
    their independent lives

68
Exogenesis
  • proposes that life originated elsewhere in the
    universe and was transferred to Earth
  • panspermia - the theory that microorganisms or
    biochemical compounds from outer space are
    responsible for originating life on Earth and
    possibly in other parts of the universe where
    suitable atmospheric conditions exist
  • panspermia can be either interstellar (between
    star systems) or interplanetary (between planets
    in the same solar system)
  • interplanetary transfer of material is well
    documented, as evidenced by meteorites of Martian
    origin found on Earth - claims that these carry
    evidence of extraterrestrial lifeforms have
    either been proven unfounded as a result of
    terrestrial contamination, misinterpretation, or
    hoaxing

69
Panspermia Cosmic Ancestry
  • Cosmic Ancestry holds that life on Earth was
    seeded from space, and that life's evolution to
    higher forms depends on genetic programs that
    come from space
  • according to Hoyle Wickramasinghe's expanded
    theory of panspermia, there can be no origin of
    life from nonliving matter in the finite past
  • without supernatural intervention, therefore,
    life must have always existed

70
Panspermia
A low temperature transfer of Martian Meteorite
(ALH84001) from Mars to Earth. Magnetic
microscopy image of ALH84001 the exterior
(upper left) has been remagnetized by the heat of
entry into the Earths atmosphere, while the
interior of the meteorite retains the weaker,
mixed magnetism it acquired on Mars
71
A
C
B
north
south
Magnetization of magnetic material. (A) Above
Curie temperature (B) Below Curie point without
external magnetic field (C) Below Curie point
with external magnetic field.
72
(Weiss et al. 2000)
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