Early Earth and the Origin of Life

nEarth formed about 4.5 billion years ago

nBombarded by huge rocks until about 3.9 billion years ago

nLife on Earth originated b/w 3.5-4.0 billion years ago

nFossils resembling filamentous bacteria

nPossible earliest life form emerged earlier


Origin of Life

nProkaryotes dominated the Earth 3.5-2.0 billion years ago

nStramatolite – fossil mats

nFossils of 3.2 billion year old prokaryotes in sediments around hydrothermal vents

nOxygen began accumulating in the atmosphere 2.7 billion years ago

nProkaryotes capable of non-oxygen producing photosynthesis

nCyanobacteria evolve to produce O2 by photosynthesis

Eukaryotic Life Begins!

nEukaryotic life began by 2.1 billion years ago

nMulticellular eukaryotes evolved by 1.2 billion years ago

nOldest eukaryotic fossils – small algae

n“snowball Earth” hypothesis – severe ice age 750-570 million years ago

nCambrian period begins the Paleozoic era

nPaleozoic “ancient animal”

nOrigin of most modern animal phyla

Colonization of Land

nPlants, fungi, and animals colonized land during early Paleozoic era (500 million years ago)

nMesozoic Era (“middle animal”)

nAge of reptiles

nDominated by gymnosperms (cone-bearing plants

nAngiosperms (flowering plants) appear

nCenozoic Era (“recent animal”)

nMajor radiation of mammals, birds and pollinating insects

Humans Appear

nHomo sapiens appear 100,000-200,000 years ago


nThe first cells may have originated by chemical evolution on a young Earth

nBelieve life evolved from non-living materials that became ordered into collection of molecules capable of self-replication and metabolism.


Resolving the Biogenesis Paradox

nBiogenesis – principle that all life arises from pre-existing life

nPasteur’s experiments (1862) disproved spontaneous generation

nSpontaneous origin of life attributed to extreme environmental conditions on early Earth

A Four Stage Hypothesis for the Origin of Life

nThe abiotic synthesis of small organic molecules

nThe joining of monomers into polymers

nThe origin of self-replicating molecules that provided for inheritance

nPackaging of these molecules into membrane-enclosed droplets (protobionts)

What do scientists think the primitive Earth was like??

nSeas, volcanoes, and large amounts of uv radiation

nAtmosphere of H20, CO, CO2, N2, CH4 and NH3

nReducing atmosphere (electron adding)

nAvailable energy from lightening and uv radiation

Early Earth

nReducing atmosphere + available energy à facilitated abiotic synthesis of organic molecules

nHot lava rocks, clay, or pyrite may have aided in the polymerization of monomers (dehydration synthesis)

nAlternative hypothesis à

ndeep sea vents may have provided needed energy and chemical precursors

nOrganic compounds form in gas clouds between stars and reach Earth on meteorites

1.) Abiotic synthesis of organic monomers is a testable hypothesis

nOparin and Haldane (1920s) hypothesized condition on the primitive Earth

nMiller and Urey (1953) apparatus that simulated hypothesized early Earth à produced a variety of amino acids and other organic compounds from inorganic molecules

2.) Monomersà Polymers

nResearchers have created polypeptides by dripping dilute solutions of organic monomers onto hot snad or lava rocks in the lab (Primordial Soup Lab)

nDehydration synthesis because water is formed during the making of the peptide

3.) Inheritance

nRNA may have functioned as the 1st hereditary material and the 1st enzymes

nShort strands of RNA capable of self replicating

nRNA catalysts called ”ribozymes” (Cech) indicated RNA capable of ribozyme-catalyzed synthesis

nNatural selection in an RNA world – most stable auto-catalytic RNA more successful at generating families of similar sequences

nRNA directed protein synthesis à enzymes to help the RNA molecule replicate

4.) Protobionts can form by self-assembly


naggregates of abiotically produced organic molecules

nCell-like microspheres

nForm spontaneously

nOrganic ingredients + lipids à liposomes (lipid bilayer droplet) has selective permeability across the membrane

nOrganic ingredient + lipids + enzymes à capable of absorbing substrates, catalyzing reactions and releasing products

Micro-spheres become more life-like in function

nNatural selection probably refined protobionts containing heredity information

nDebate about origin of life continues

nLaboratory simulations are hypotheses

Characteristics of Cell-like Microspheres

The Major Lineages of Life

nArranging life into kingdom’s is a work in progress

nWhittaker (1969) proposed a five (5) kingdom classification (Figure 15.14A)

nProkaryotes à Monera


nProtista – unicellular or simple multicellular

nPlantae – autotrophic

nFungi – absorptive heterotrophs

nAnimalia – ingest and digest

Three Kingdom Classification

nThree major evolutionary lineages (super-kingdoms)

nBacteria à Eubacteria

nArchaea à Archaebacteria (ancient)





nProtists à five or more kingdoms



Why a Scientific Classification System?

nAmbiguity of terms

nLatin “dead language”

nCategorization of relationships:




(NOT habitat)


7 Classification Groups:

nKingdom (most inclusive)






nSpecies (most specific)









5 Major Kingdoms:






n1 cell, prokaryotes

n1 cell, eukaryotes & algae

nMulticelled, absorptive feeders

nMuticelled,  autotrophs

nMuticelled heterotrophs

Which is the most difficult to assign?


nMost specific

nSuccessful interbreeding

nFertile offspring

Which group has the largest # organisms?


nCell types ProkaryotesEukaryotes

nCell number




Plant Kingdom


nCommon names

nHave evolved over centuries in a multitude of languages

nSometimes used only in  a limited geographical area

nProblem with common names:

nOne plant may be known by several names in different regions, and the same name may be used for several different plants…

Scientific names

Similar plant species form a group called a genus (plural: genera)…

Genera are grouped into families…

Families into orders, classes, divisions and kingdoms




“King David Came Over For Great Spaghetti”

“King David Conquered Our Fifty Great States”

Species name

Each species has a single correct scientific name in Latin called a binomial (two names) – it is always italicized or underlined.


First name is genus name.

Second name is species name


Human:  Homo sapiens              

Cat:         Felis catus                            

Dog:        Canis familiaris                      Wolf: Canis lupus


Genus of maple trees is Acer


It has many species including:


Common name                            Scientific name

“Red maple”                              Acer rubrum

“Sugar maple”                           Acer saccharum

“Black maple”                            Acer nigrum

Taxonomic hierarchy

Species that have many characteristics in common are grouped into a genus.

Related genera that share combinations of traits are grouped into families.

Families are grouped into orders.

Orders into classes

Classes into divisions (or phyla for animals)

Related divisions/phyla are grouped into kingdoms


(e.g. house, street, city, county, state, country, continent, planet)

What is a species?

Species: a set of individuals that are closely related by descent from a common ancestor and ordinarily can reproduce with each other, but not with members of any other species.


Biological species: group of interbreeding populations. Offspring are fertile.


Some members of same species look very different…







Definition of species

nOr, plants look the same, but due to  polyploidy
(more than the diploid number of chromosomes), they cannot interbreed.

nFor example: Ferns;  evening primrose

Carolus Linnaeus

nSwedish scientist – Carl von Linne

            (doctor and botanist)

            born in 1707.



nCalled the “Father of Systematic Botany”

nEstablished modern system of nomenclature


Linnaeus legacy

His binomial system of nomenclature, in which the genus and species names are used.


He classified 12,000 plants and animals, and many of the names he first proposed are still in use today…

Animal Kingdom

Scientific Name:


nItalics or underlined

nGenus species

nHomo sapien

Classification Criteria:



nHair Color

nGenetic System

nEvol. History


nMolecular Make-up

nMost (DNA)

nNot very

nNot very




nNot very

Similar Categories:






Similar Categories:





Did Man evolve from Apes?


nSimilar ancestor








Mammals arise from Theraapsids


Chimpanzees: distant relatives

Walking upright:


Lemurs: distant relatives

The ruffed lemur lives in the eastern rain forests of Madagascar. The lemurs and their relatives are believed to have evolved in isolation from the monkeys and apes after Africa became separated from Madagascar over 50 million years ago. Since the arrival of humans on Madagascar over 2000 years ago, at least 14 species of lemurs are believed to have become extinct.


When Charles Darwin published The Descent of Man in 1871, he challenged the fundamental beliefs of most people by asserting that humans and apes had evolved from a common ancestor. Many critics of Darwin misunderstood his theory to mean that people had descended directly from apes. This caricature of Charles Darwin as an ape appeared in the London Sketch Book in 1874. Homologous or Analogous Stuctures?

Homologous Structures:

nShark/Dolphin fin

nSeal flipper/Fish fin

nFish tail/Whale fluke

nBat wing/Cat limb

nBird/Insect wing

nBird wing/reptile limb

nSeal flipper/human arm

nDog limb/whale flipper


nNo (cartilage/rays)

nNo (bones/rays)

nYes (bones/bones)

nYes (bones/bones)

nYes (bones/no bones)


nYes(mammal bones)

nYes(mammal bones)


Family or Genus Relations?


nLess closely related

nLarger group


nMore closely related

nPrecedes species=



nLions, tigers, leopards

nhouse cats,cheetahs, ocelots

Genus: Panthera

nLeopards (pardus)

nLion (leo)

nTigers (tigris)

Feline Family Members:


Genus: Panthera (Lions &Tigers)

Classification by characteristics:

nFossil Skulls

nDNA Sequences

nHair Samples