TOPICS: • THE CONCEPT OF LIFE • WHAT QUALIFIES SOMETHING AS “LIVING”? o MOVEMENT o SENSITIVITY o DEATH o COMPLEXITY • THEORIES ON THE ORIGIN OF LIFE o EXTRATERRESTRIAL ORIGIN o PANSPERMIA o DIVINE CREATION o ORIGIN FROM NONLIVING MATTER (PHYSICO-CHEMICAL THEORY) • FORMATION OF THE FIRST CELL • EARLY LIFE FORMS

1. INTRODUCTION
TO LIFE SCIENCE

2. I. THE CONCEPT
OF LIFE

3. WHAT QUALIFIES SOMETHING
AS “LIVING”?
1. Movement
– Most animals move
• movement from one
place to another is not
diagnostic of life
– The criterion of
movement is neither
necessary nor
sufficient.

4. WHAT QUALIFIES SOMETHING
AS “LIVING”?
2. Sensitivity
– Almost all living things respond
to stimuli
– Plants grow toward light, and
animals retreat from fire
– Not all stimuli produce
responses
– This criterion is inadequate to
define life.

5. WHAT QUALIFIES SOMETHING
AS “LIVING”?
3. Death
– All living things die, while inanimate objects do
not.
– Unless one can detect life, death is a meaningless
concept

6. WHAT QUALIFIES SOMETHING
AS “LIVING”?
4. Complexity
– All living things are
complex.
– Complexity is a
necessary criterion of
life, but it is not
sufficient in itself to
identify living things.

7. It took the Earth nearly 1
billion years to cool enough
for the first life forms to
appear

8. • Earth is much older than life
– Earth= 4.5 billion years old
– Oldest Fossil= 3.5 billion years old
*Based on radioactive decay studies of
rocks

9. A. HOW DID LIFE BEGIN?
THEORIES ON THE ORIGIN OF LIFE
- Basic enigma of life
HOW DID LIFE ORIGINATE?
Several intelligent explanations
account for the origin of life

10. THEORIES ON THE ORIGIN OF LIFE
1. Extraterrestrial Origin
– life originated on another
planet outside our Solar
System
– life was then carried to
Earth on a meteorite or an
asteroid and colonized
Earth
* not proven

11. THEORIES ON THE ORIGIN OF LIFE
2. Panspermia
– Gk., “seeds everywhere”
– a.k.a Cosmozic Theory
– the “seed” of life exists all
over the universe and can be
propagated through space
• contains extremophile
organisms or organisms that
survive in extreme conditions
• life, then had come to earth in
the form of resistant spores.
Illustration of a comet
(center) transporting a
bacterial life form (inset)
through space to the Earth
(left)

12. PANSPERMIA THEORY
• Proposed by Richter in 1865 and supported
by Arrhenius.
– Life had come to earth from other planets of the
universe, in the form of resistant spores.
• British astronomers Fred Hoyle and Chandra
Wickramasinghe proposed that:
– interstellar dust and comets contain organic
compounds.
– comets, which are largely made of water (ice),
carry bacterial life across galaxies and protect it
from radiation damage along the way.
• the 2005 Deep Impact mission to Comet Tempel 1
discovered a mixture of organic and clay particles inside
the comet.

13. 2005 DEEP IMPACT MISSION
• Deep Impact was a NASA space probe
launched from Cape Canaveral Air
Force Station at 18:47 UTC on January
12, 2005.
• It was designed to study the interior
composition of the comet Tempel 1
(9P/Tempel), by releasing an impactor
into the comet.
• At 05:52 UTC on July 4, 2005, the
impactor successfully collided with the
comet's nucleus.
• The impact excavated debris from the
interior of the nucleus, forming an
impact crater.
• Photographs taken by the spacecraft
showed the comet to be more dusty and
less icy than had been expected.
• Analysis of data from the Swift X-ray
telescope showed that the comet
continued outgassing from the impact
for 13 days, with a peak five days after
impact.
• A total of 5 million kilograms (11
million pounds) of water and between
10 and 25 million kilograms (22 and 55
million pounds) of dust were lost from
the impact.

14. VARIATIONS OF PANSPERMIA
THEORY
1. Lithopanspermia (interstellar panspermia)
– impact-expelled rocks from a planet's surface
serve as transfer vehicles for spreading biological
material from one solar system to another.
2. Ballistic Panspermia (interplanetary panspermia)
– impact-expelled rocks from a planet's surface
serve as transfer vehicles for spreading biological
material from one planet to another within the
same solar system

15. VARIATIONS OF PANSPERMIA
THEORY
3. Directed Panspermia
– the intentional spreading of the seeds of life to
other planets by an advanced extraterrestrial
civilization or the intentional spreading of the
seeds of life from Earth to other planets by
humans
• there is a chance that humans, at some point in our
space explorations, may unintentionally transport
microorganisms on manned craft or unmanned probes
to other planetary bodies.

16. VARIATIONS OF PANSPERMIA
THEORY
3. Directed panspermia
– Proposed by:
• The late Nobel prize winner Professor Francis Crick,
and British chemist Leslie Orgel
– Crick found it impossible that the complexity of
DNA could have evolved naturally.
– He proposed that small grains containing DNA, or
the building blocks of life, could be loaded on a
brace of rockets and fired randomly in all
directions.

17. THEORIES ON THE ORIGIN OF LIFE
3. Divine Creation
– life was put on Earth by
divine forces
– common to many of the
world’s religions and
cultures

18. INTELLIGENT DESIGN
• Creationists
– tried to imply that:
• life is so complex and specialised that it
could only have come about through the
design of a supernatural creator
• once created it remained the same through
time
– reject the fact that
• new species can come about by the natural
selection of chance mutations

19. SPECIAL CREATION IS BASED ON
BELIEF
• As these ideas are developed from a
theological view point they are impossible to
test
• Creationists focus on trying to disprove the
theory of evolution rather than by testing
their own hypothesis
• A scientific fact is an observation that has
been repeatedly confirmed and for practical
purposes is accepted as true
– special creation fails this criterion

20. SPECIAL CREATION IS BASED ON
BELIEF
• The non-scientific hypothesis
• Some supernatural being brought life into
existence from nothing
• Literal interpretation of religious documents
– 9:00am on 23rd October 4004BC

21. THEORIES ON THE ORIGIN OF LIFE
4. Origin from Nonliving
Matter (Physico-chemical
Theory)
– life arose form inanimate
matter after Earth cooled
– random events probably
produced stable molecules
that could self-replicate

22. THEORIES ON THE ORIGIN OF LIFE
4. Origin from Nonliving
Matter (Physico-chemical
Theory)
– natural selection favored
changes in the rate of
reproduction
• eventually led to the first
cell

23. THEORIES ON THE
ORIGIN OF LIFE
1. Extraterrestrial Origin
2. Panspermia
3. Divine Creation
4. Origin from Nonliving
Matter (Physico-
chemical Theory)
*Abiogenesis Theory

24. B. ORIGIN FROM NONLIVING MATTER
• Life began when conditions were quite
different from the current environment
– Atmosphere before
• lack of oxygen
• rich in carbon dioxide, carbon monoxide, hydrogen
and nitrogen
– Earth’s surface before
• bombarded with meteorites, volcanic eruptions and
intense radiation from the sun

25. B. ORIGIN FROM NONLIVING MATTER
• Under those conditions, life may have
originated from nonliving matter
– nonliving matters = chemicals that already
existed in the environment
• water and clay
• minerals in the ocean
• gases present in the atmosphere

26. Atmospheric water vapor condensed into rain.
Eroded surface. Washed minerals into seas.
Chemicals from atmosphere mixed and
reacted with those in the waters
=PRIMORDIAL SOUP
formed many hydrocarbons.

27. B. ORIGIN FROM NONLIVING MATTER
• The energy present on Earth caused the chemicals
to react with one another, forming the complex
molecules:
• Amino acids
• DNA
• Carbohydrates and Lipids
* these made life possible
• Energy for chemical reactions between these gases
could come from electric discharge in storms or
solar energy (no ozone layer)
– the Earth’s surface temperature probably hotter than
today.

28. Oparin pointed out that the transformation of lifeless chemicals
into living matter extended over a period of almost a billion years.
He also argued that such a transformation would not be possible
today, since any particle approaching the form of life would be
decomposed by the oxygen of the air or destroyed by
The view that life
emerged through a long
process of chemical
evolution was set forth by
the Russian biochemist
Alexander Oparin in 1924.

29. 1.5 U.2 The first cells must have arisen from non-living material.
Primitive ‘Soup’ (ocean surface)
• Haldane and Oparin (~1920s)
proposed that life arose from
nonliving conditions by means
of a series of changes (and
increasing complexity) in
molecular composition as a
result of the reducing, high
energy environment that
existed on early Earth (between
4.6-3.8 bybp (billion years
before present)
• Proposed the Prebiotic Broth
Hypothesis
• Not tested until 1950s
• Tested by Stanley Miller and
Harold Urey

30. C. HOW THE MOLECULES WERE
FORMED
• Stanley Miller
– American chemist
– performed experiment that replicated the early
Earth conditions
– together with Harold Urey, they proved that
amino acids and other organic molecules can be
formed

31. C. HOW THE MOLECULES WERE FORMED
• Stanley Miller’s
experiment:
– water was heated
– water vapor mixed with
hydrogen, carbon dioxide,
carbon monoxide,
nitrogen, ammonia and
methane
– the mixture of gases was
sparked with electricity to
simulate lightning

32. D. HOW THE MOLECULES WERE FORMED
• Stanley Miller’s experiment:
– the gases were cooled using a
glass tube filled with
circulating cold water
RESULT:
• a dark mixture containing
amino acids and other complex
molecules were formed
• Amino acids= building blocks of
proteins

33. • Using slightly different combinations of
starting molecules, Miller and other
scientists were able to generate:
• Many amino acids
• RNA and DNA nucleotides
• Lipids
• Carbohydrates
• Adenosine Triposphate (ATP)

34. C. FORMATION OF THE FIRST CELL
• scientists think that the formation of tiny
spheres of lipids may have been the first
stage in the origin of the cell
– when lipids mix with water, they form bubbles
called coacervate

35. Coacervates (Microspheres)

36. Ocean Froth
• The waves crashing
on the shore
consisted of bubbles
(froth)
• The “membranes” of
the bubble were
either made of
– hydrocarbon
chains/lipids
– Protenoids (chains of
amino acids)

37. Experiments have shown that
phospholipids natural assemble into
bilayers, if conditions are correct.
Formation of the bilayer creates an
isolated internal environment.
The formation of an internal
environment means that optimal
conditions, e.g. for replication or
catalysis can be maintained.
C. FORMATION OF THE FIRST CELL

38. C. FORMATION OF THE FIRST CELL
• double layered membranes of bubbles
– similar to the lipid bilayer of the cell membrane
• cell membrane
– the crucial feature that separates the cell from
its environment
– contain lipid

39. C. FORMATION OF THE FIRST CELL
• It was believed that:
– the early oceans might have contained
numerous small lipid coacervates that formed
and eventually dispersed
• Coacervates are unable to obtain energy
from materials found in its environment
– however, they might have developed these
capabilities and were able to transfer these to
other coacervates over time

40. C. FORMATION OF THE FIRST CELL
• Scientists further hypothesized that
– for millions of years, coacervates that floated in
the oceans joined together to form larger
molecules
• these molecules reacted with each other forming a
more complicated structures that has the ability to
replicate
– The molecules then developed into cell-like
structures

41. • An addition to the theory that life may have
formed close to the oceans surface, early life may
have formed at hydrothermal vents on the ocean
floor
• Today, hydrothermal vents provide basic materials
to support living organisms in environments where
there is no light, very little energy, and little other
perturbation
• Ammonia is produced in abundance at such
locations, suggesting that it could possibly be built
into nucleic acid bases and the possibly into amino
acids

42. Sea Vents
http://upload.wikimedia.org/wikipedia/commons/b/b8/Deep_sea_vent_chemistry_diagram.jpg

43. •The current “most accepted“ theory of life evolving hypothesizes an
RNA world
•RNA in the early world would have functioned as a self replicating
molecule, eventually developing a number of minimal catalytic
properties
self-replicates Proteins take
over catalysis
DNA becomes
long term storage
and major coding molecule
Packaging evolves
- RNA codes
and catalyses
RNA
Molecular Reproduction

44. The RNA World Hypothesis
• Proposed by Walter Gilbert, mid 1980s
• Concept of RNA catalyzing critical pre-biotic and early biological
reactions
• RNA would give rise to RNA as an informational molecule
• RNA would give rise to protein
• RNA might bind amino acids proteins
• RNA might give rise to DNA
• Proteins might take over some functions
• DNA would take over informational functionality
• Eventually giving rise to the DNA RNA protein scheme
found today

45. C. FORMATION OF THE FIRST CELL
• Scientists believe that the
first cells were the
prokaryotes
– PROKARYOTES= organisms
whose cells have no nucleus
• The first prokaryotes were
anaerobic
= they did not need and could
not tolerate free oxygen

46. C. FORMATION OF THE FIRST CELL
• Organisms that need oxygen could not have
survived because Earth lacked free oxygen
• Many anaerobic prokaryotes still live today
in places where there is no free oxygen

47. First Eukaryotes (about 2 billion years ago)
• Development of internal membranes
– create internal micro-environments
– advantage: specialization = increase efficiency
• natural selection!
infolding of the
plasma membrane
DNA
cell wall
plasma
membrane
Prokaryotic
cell
Prokaryotic
ancestor of
eukaryotic
cells
Eukaryotic
cell
endoplasmic
reticulum (ER)
nuclear envelope
nucleus
plasma
membrane

48. Endosymbiosis
Ancestral
eukaryotic cell
Eukaryotic cell
with mitochondrion
internal membrane
system
aerobic bacterium mitochondrion
Endosymbiosis
• Evolution of eukaryotes
– origin of mitochondria
– engulfed aerobic bacteria, but did not digest them
– mutually beneficial relationship
• natural selection!

49. mitochondrion
chloroplast
Eukaryotic cell with
chloroplast & mitochondrion
Endosymbiosis
photosynthetic
bacterium
• Evolution of eukaryotes
– origin of chloroplasts
– engulfed photosynthetic bacteria,
but did not digest them
– mutually beneficial relationship
• natural selection!
Eukaryotic
cell with
mitochondrion

50. • Evidence
– structural
• mitochondria & chloroplasts resemble bacterial structure
– genetic
• mitochondria & chloroplasts have their own circular DNA, like
bacteria
– functional
• mitochondria & chloroplasts move freely within the cell
• mitochondria & chloroplasts reproduce independently from
the cell
Theory of Endosymbiosis

51. C. FORMATION OF THE FIRST CELL
• Four main stages:
– Abiotic (nonliving) synthesis of small organic
molecules such as amino acids and nitrogenous
bases
– Joining of these small molecules into
macromolecules such as proteins and nucleic
acids (RNA and DNA)

52. C. FORMATION OF THE FIRST CELL
• Four main stages:
– Packaging of molecules into protocells (droplets
with membranes that maintained an internal
chemistry different from that of their
surroundings
– Origin of self-replicating molecules that
eventually made inheritance possible

53. II. EARLY LIFE FORMS
• Oldest rock= 3.8 years old
– no fossils have been found
• Oldest fossil
– found in 3.5 billion year-old rocks
• once were sediments in on the
ocean floor
• tiny fossils= BACTERIA

54. BACTERIA
• classified according to the composition of their cell
walls and cell membrane
1. Eubacteria
– true bacteria
2. Archaebacteria
– ancient bacteria
– rare
– found mainly in hostile environments
• salty lakes, hot springs, swamps, ocean floor
– resemble those of early Earth

55. • Today, biologists believe that the
oxygen of early Earth’s
atmosphere was produced by
bacteria
– about 3 BYA, a group of
photosynthetic bacteria
(CYANOBACTERIA) evolved
• as they carried out photosynthesis,
oxygen was released into the oceans
• after hundreds of millions of years,
the oceans were soaked with oxygen
• the oxygen began to bubble out of the
water and into the air

56. • More oxygen was then added over the billions
of years
– lead to the present composition of the atmosphere
• this change enabled life to move onto land
– as cyanobacteria added oxygen gas to the
atmosphere, large amounts of oxygen began to
diffuse into the atmosphere, producing OZONE

57. • Before the ozone was formed, life was
restricted to the oceans
– but due to the new ozone layer that acted like a
shield which blocked ultraviolet radiation, the
radiation levels on Earth’s surface went down
• this allowed movement of life onto dry land

58. • More complex life forms then appeared
– Eukaryotes
• much larger than prokaryotes
• contained a central nucleus and a complicated
internal structure
• evolved into organisms that are composed of many
cells
• first single-celled eukaryote evolved around 2 BYA
• ancestor of all plants and animals that exist today

60. • Plants and fungi
– first living things to populate the surface of the land
– the solution to the challenge of living on dry land
was a unique mutualistic partnership between plant
and fungi (mycorrhizae)
• plants provide food to the fungi
• fungi provide nutrients obtained from organic matters
• MYCORRHIZAE= close associations between the roots of the
plants and fungi
= fungi grow on or into the plant root and
then branch out into rock or soil

61. • Fossil record revealed that:
– plants covered the surface of the Earth within
80 million years of their initial invasion
– animals soon followed
• ARTHROPODS
– first animals to leave the water
– animals with hard body covering and jointed legs

63. • SCORPIONS
– first arthropods to live on
land
– carnivorous relatives of
spiders
– with 2 large pincers on their
front legs and a venomous
stinger at the end of their
tails

64. • Major events showing how life originated on Earth
– 4.5 BYA= earth formed
– 4.0 BYA= oldest rocks
– 3.5 BYA= first bacteria appeared
– 3.0 BYA= bacteria diversified
– 2.5 BYA= photosynthesis began
– 2.0 BYA= diverse and abundant bacteria
– 1.5 BYA= first eukaryotes
– 1.0 BYA= earliest animals, first multicellular organisms,
diverse protists
– 0.5 BYA= rapid diversification of animals; plants and fungi
appeared
– 2 MYA= origin of humans

65. • Major events showing how life originated on Earth
since 4.5 BYA
– for 2 billion years, bacteria were the only living things
on the planet
– in the last 570 million years, there was a rapid
diversification of multicellular life
• plants, fungi and most major animal groups evolved
– insects (terrestrial arthropod) evolved from scorpions
• more than 70% of the animal species
• first animals to develop wings

66. • Evolution of more complex animals
– worm-like animal= earliest known animals w/ notochord
• NOTOCHORD= develops into vertebral column chordates
or animals with notochords are called VERTEBRATES
– JAWLESS FISH WITH BONY SKELETONS- earliest
vertebrates
• appear to have fed in a head-down position with their fins
helping to keep them upright while they suck up organic
materials from the bottom
• for over 100 million years, jawless fishes were the only
vertebrates

67. • JAWLESS FISH WITH BONY SKELETONS
– today, are the eel-like, PARASITIC LAMPREYS
and SCAVENGING LAMPREYS
– they then evolved after approx. 400 MYA
• Sharks and bony fishes

68. • AMPHIBIANS
– first vertebrates on land
– evolved from bony fishes about 350 MYA
• REPTILES
– evolved from amphibians about 300 MYA
– the earliest reptiles gave rise to a variety of species that
replaced the amphibians as the dominant terrestrial animals
– the massive reptiles known as dinosaurs arose about 220 MYA
• For more than 150 million years, mammals and reptiles
coexisted
– during this time, mammals were small and did not diversified

69. • Although most dinosaurs are now extinct,
descendants of small insect-eating dinosaurs still
exist- the BIRDS
– bird feathers evolved from the same scales that
protected the dinosaurs as well
• Birds, mammals and dinosaurs coexisted until
the sudden extinction of dinosaurs 65 million
years ago during the Cretaceous period
– this caused birds and mammals to diverge
rapidly and fill the nearly-empty Earth

70. III. A BRIEF HISTORY OF LIFE

71. ERA: ARCHEOZOIC
• Period: PRECAMBRIAN
• Age: 4,500-550 mya (million years ago)
• Life forms:
– First single- celled organisms
– Simple plants
– Invertebrate animals
• Algae
• Bacteria
• Jelly fish
• Flagellates
• Amoebas
• Worms
• Sponges

72. ERA: PALEOZOIC
• Period: CAMBRIAN
• Age: 550- 505 mya
• Life forms:
– First trilobites
– Forams
– Brachiopods
– Nautiloids
– Clams
– Snails
– Crustaceans
– Crinoids
– Gastropods
– Corals
– Protozoans

73. ERA: PALEOZOIC
• Period: ORDOVICIAN
• Age: 505- 438 mya
• Life forms:
– First starfish
– Sea urchins
– Blastoids
– Eurypterids
– Bryozoa
– Scaphopods
– Jawless fish
– Echinoids

74. ERA: PALEOZOIC
• Period: SILURIAN
• Age: 438- 408 mya
• Life forms:
– First land plants
– Ferns
– Sharks
– Bony fishes
– Scorpions

75. ERA: PALEOZOIC
• Period: DEVONIAN
• Age: 408-360 mya
• Life forms:
– First insects
– Tetrapods
– Ammonites
– Placoderms

76. ERA: PALEOZOIC
• Period: CARBONIFEROUS
• Epoch
– Mississippian- 360-325 mya
• Life forms:
– First reptiles
– Spiders
– Amphibians
– Pennsylvanian- 325-286 mya
• Life forms:
– First conifers
– Synapsids

77. ERA: PALEOZOIC
• Period: PERMIAN
• Age: 286-248 mya
• Life forms:
– Heyday of synapsids including
pelycosaurs

78. ERA: MESOZOIC
• Period: TRIASSIC
• Age: 248-213 mya
• Life forms:
– First turtles
– Cycads
– Lizards
– Dinosaurs
– Mammals

79. ERA: MESOZOIC
• Period: JURASSIC
• Age: 213-145 mya
• Life forms:
– First squids
– Frogs
– Birds
– Salamanders

80. ERA: MESOZOIC
• Period: CRETACEOUS
• Age: 145-65 mya
• Life forms:
– First flowering plants
– Snakes
– Modern fish
– Rise and fall of toothed birds
– Heyday of dinosaurs

81. ERA: CENOZOIC
• Period: TERTIARY
• Epoch:
– Paleocene
• Diversification of mammals
– Eocene
• First marine and large terrestrial animals,
horses, whales and monkeys
– Oligocene
• First grasses, apes, anthropoids
– Miocene
• First hominids
– Pliocene
• First Australopithecines

82. ERA: CENOZOIC
• Period: Quaternary
• Epoch:
– Pleistocene
• Mammoths, mastodons,
Neanderthals
– Holocene
• First modern human beings