ORIGIN AND HISTORY OF LIFE
Origin of Life
 Darwin’s theory is based around the idea of a
common ancestor that all living organisms
can be traced back to.
 This ancestor is called the Last Universal
Common Ancestor or LUCA.
Origin of Life
 Since Darwin, advances in chemistry,
evolutionary biology, paleontology,
microbiology and other fields of science, have
helped develop new hypothesis about the
origin of life.
 There is now a body of scientific evidence
that life began 3.5-4 billion years ago and
developed in 4 stages.
Origin of Life
 Stage 1- Organic Monomers
 Simple organic molecules evolved from inorganic
monomers. Ex: Amino Acids and Nucleotides
 Stage 2- Organic Polymers
 Organic monomers joined to form polymers. Ex. DNA,
RNA, and proteins
 Stage 3- Protocells
 Polymers became enclosed by membranes to form the
first cell precursors.
 Stage 4- Living Cells
 Protocells began self replicating and gained other
cellular properties.
Stage 1- Monomers
 The Oparin- Haldane hypotheis, also known
as the “primordial soup hypothesis” proposed
that the lack of oxygen in the atmosphere
gave ammonia (NH3) and Methane (CH4)
strong reducing capability. Therefore, the
redox reactions in the early atmosphere could
have powered the chemical evolution of
organic monomers from inorganic molecules.
Stage 1- Monomers
 In 2008 a group of scientist re-tested the
Miller-Urey experiment and found a greater
variety of organic materials than Miller
reported.
 The iron-world hypothesis, proposed by
Gunter Wachterschauser, stated that thermal
vents emitted all the elements necessary for
organic monomers to synthesize.
Stage 1- Monomers
 Some scientist believe that the early organic
monomers could have been brought to Earth
by comets and meteorites.
Stage 2- Polymers
 The Iron-sulfur World Hypothesis
 Research has found that organic monomers will
react in the presence of iron-nickel sulfides found
at thermal vents.
Stage 2- Polymers
 Protein-First Hypothesis
 Sidney Fox found that amino acids will polymerize
in the presence of dry heat. He proposed that
when amino acids floating in the ocean were
exposed to the sun, they formed proteionoids,
small polypeptides that have some catalytic
activity.
Stage 2- Polymers
 RNA- First Hypothesis
 This hypothesis suggests that only RNA was
needed to progress towards the first cell(s).
 In a study by Cech and altman, they discovered
RNA can act as both a substrate and an enzyme.
Based on their findings and the fact that some
viruses have RNA, it would seem that RNA could
have carried out processes of life associated with
DNA and proteins today.
Stage 3-Protcells
 Protocells are precursors to true cells.
 The formation of an outer membrane was
essential to regulation and maintenance of
cellular functions.
 The plasma membranes of today’s cells are
formed from a phospholipid bilayer. Early
membranes were likely composed of fatty
acids, which are smaller than phospholipids
but still have a hydrophobic tail and
hydrophilic head.
Stage 3- The protocell
 When put in water, fatty acids will assemble
into small spheres call micelles with heads
pointing out and tails pointing in.
 If conditions are right, then they can form a
bilayer called a vesicle.
Stage 3- The protocell
 The first cells would have evolved some way
to obtain nutrients.
 Because they were formed by thermal vents,
it’s probable that they carried out
chemosynthesis (the synthesis of organic
molecules from inorganic molecules and
nutrients) before they evolved the ability to
break down organic materials.
Stage 4- Self- Replication
 In modern cells, DNA directs protein
synthesis and information flows from DNA to
RNA to protein.
 It is possible that this sequence developed in
stages.
 RNA-first Hypothesis- RNA would have first
regulated protein synthesis until DNA could
evolve
 Protein- first hypothesis- proteins developed first
and then once a membrane was evolved could
DNA and RNA evolve.
History of Life
 Relative Dating of Fossils
 Even before the theory of evolution, scientist were
trying to age the strata layer
 Geologists used index fossils (fossils used to
identify deposits made at the same time) to
relatively date the age of the layer
 Absolute Dating
 Rely on radiometric techniques to assign actual
dates to fossils.
 Most common technique is Carbon-14 dating.
 Carbon-14 is a rare isotope of carbon that has a half
life of 5,730 years
 Only accurate for fossils up to 100,000.
The Precambrian Time
 The precambrian time comprises about 87% of
the geologic timescale.
 This is when life began.
 The first modern cells were probably
prokaryotes, appearing approximately 3.5 bya.
 The first identifiable fossils are complex prokaryotes
 The oldest were discovered in west Australia date back
3.46 bya.
The Precambrian Time
 Eukaryotic Cells Arise
 Eukaryotes originated around 2.1 bya once
oxygen was added to the atmosphere.
 The nucleus may have developed by an
invagination of the plasma membrane.
 The endosymbiotic theory states that a nucleated
cell engulfed prokaryotes, which then became
organelles.
 Evidence to support this theory
 Present day mitochondria and chloroplasts have
relatively the same size range as bacteria.
 Mitochondria and chloroplasts have their own
DNA and make some proteins.
 Mitochondria and cholorplasts divide by binary
fission.
 Outer membrane of mitochondria resemble
eukaryotic cells and the inner resemble bacterial
cells
 Multicellularity Arises
 Multicellular protists fossils have been found in
Canada dating back to 1.4 BYA
 These gave rise to the invertebrates, whose fossils
date back to 630-545 mya.
The Paleozoic Era
 The paleozoic era lasted about 300 million
years.
 There were 3 major mass extinctions during
this time period.
 57% of marine species
 Over 50% coastal species
 Over 50% of corals
The Paleozoic Era
 The Cambrian Period (542 mya)
 Referred to as the Cambrian Explosion
 All of today’s animals can trace their ancestry back
to this time.
 Animals had a hard exoskeleton.
The Paleozoic Era
 Life began to move onto land around 500
mya.
 Algae started invading damp areas on land
during the Ordovician period.
 Insects entered the fossil records during the
Carboniferous period.
 Vertebrates descent began during the
Orovician period with the jawless fishes.
The Mesozoic Era
 Carboniferous Period 359-299 mya
 Permian Period 299-251 mya
 Triassic Period 251-199 mya
 Jurassic Period 199-145 mya
 Cretaceous 145-65 mya
The Mesozoic Era
 Reptiles can be traced back to The permian
period.
 The average size of dinosaurs were about the
size of a crow, although there were a few
giant species.
 At the end of the Cretaceous period,
dinosaurs became extinct.