Chapter 16 Chapter 16 Origin of LifeOrigin of Life

The Big Bang The Big Bang TheoryTheory

Big Bang DetailsBig Bang Details Galaxies are collections of stars, gas and dust bound Galaxies are collections of stars, gas and dust bound

together by their mutual gravitytogether by their mutual gravity

Galaxies comprise the basic building blocks of the Galaxies comprise the basic building blocks of the Universe Universe

When galaxies were born and how they evolved is When galaxies were born and how they evolved is currently a very active topic. currently a very active topic.

At present, the Universe is thought to have been At present, the Universe is thought to have been created in the created in the Big BangBig Bang, in which space and time , in which space and time were created in a simple hot energetic, state, about 15 were created in a simple hot energetic, state, about 15 billion (15 x 109 ) years ago. billion (15 x 109 ) years ago.

A technique to determine the age of items on A technique to determine the age of items on our planetour planet

Carbon 14 Carbon 14 Nitrogen 14 is used to date Nitrogen 14 is used to date fossils (good up to 50 000 yrs)fossils (good up to 50 000 yrs)

Uranium 238 – Lead 236 is used to date rocks Uranium 238 – Lead 236 is used to date rocks and is good to 4.5 billion yearsand is good to 4.5 billion years

Radiometric Radiometric DatingDating

Carbon-14 – used to date fossilsCarbon-14 – used to date fossils Carbon-14 (Carbon-14 (1414C) a rare isotope of carbon, that C) a rare isotope of carbon, that

has has 6 protons and 8 neutrons6 protons and 8 neutrons

1414C decays to C decays to 1414N at a constant rateN at a constant rate

Every 5,600 years half the Every 5,600 years half the 1414C in a sample will C in a sample will emit a beta particle (electron) and decay to emit a beta particle (electron) and decay to 1414N N

Thus 5,600 years is called the half life of Thus 5,600 years is called the half life of 1414CC

Because of Because of 1414C’s short half life, it is not useful C’s short half life, it is not useful for dating million year old fossils, it is only for dating million year old fossils, it is only accurate to about 50,000 yearsaccurate to about 50,000 years

Half-livesHalf-lives

256 14C atoms at time 0

Half-livesHalf-lives

128 14C and

128 14N atoms

after 5,600 years or

1 half-life

Half-livesHalf-lives

64 14C and

192 14N atoms

after 11,200 years or

2 half-lives

Half-livesHalf-lives

32 14C and

224 14N atoms

after 16,800 years or

3 half-lives

Half-livesHalf-lives

16 14C and

240 14N atoms

after 22,400 years or

4 half-lives

Half-livesHalf-lives

8 14C and

248 14N atoms

after 28,000 years or

5 half-lives

Half-livesHalf-lives

4 14C and

252 14N atoms

after 33,600 years or

6 half-lives

Half-livesHalf-lives

2 14C and

254 14N atoms

after 39,200 years or

7 half-lives

Carbon-14Carbon-14 1414C is used to date organic samples C is used to date organic samples

like wood, hair, shells (CaCOlike wood, hair, shells (CaCO33) and ) and other plant and animal productsother plant and animal products

Atmospheric Atmospheric 1414C is incorporated into C is incorporated into organic molecules by plants during organic molecules by plants during photosynthesisphotosynthesis

Animals that eat the plants get Animals that eat the plants get 1414C C from the plants they eatfrom the plants they eat

The current ratio of The current ratio of 1414C to C to 1212C in the C in the atmosphere is immeasurably smallatmosphere is immeasurably small

Carbon-14Carbon-14 With a relatively short half life and an With a relatively short half life and an

earth billions of years old, all Cearth billions of years old, all C1414 should be goneshould be gone

This would be true if not for This would be true if not for production of new production of new 1414C in the C in the atmosphere as a result of interactions atmosphere as a result of interactions between the upper atmosphere and between the upper atmosphere and neutrons in cosmic radiationneutrons in cosmic radiation

The atmospheric ratio of The atmospheric ratio of 1414C to C to 1212C C represents an equilibrium between represents an equilibrium between production and decay of production and decay of 1414CC

Carbon-14Carbon-14Sometime in the Ancient PastSometime in the Ancient Past

CO2 fixation

Plant absorbs both C12 and C14 in the ratio they exist in the atmosphere

Carbon-14Carbon-14A Plant Grows Absorbing COA Plant Grows Absorbing CO22

Carbon-14Carbon-14The Plant DiesThe Plant Dies

Carbon-14Carbon-14It Is BuriedIt Is Buried

Carbon-14Carbon-14Over Time Over Time 1414C Decays to C Decays to 1414NN

Carbon-14Carbon-14Over Time Over Time 1414C Decays to C Decays to 1414NN

Other Isotopic Dating MethodsOther Isotopic Dating Methods 1414CC dating is not useful for dating dating is not useful for dating

geological strata so other methods have geological strata so other methods have been developed using isotopes with much been developed using isotopes with much longer half liveslonger half lives

Examples include:Examples include:

Uranium-235 Lead-207 0.7 x 109

emissionUranium-238 Lead-206 4.5 x 109

Thorium-232 Lead-208 14.0 x 109

Rubidium-87 Strontium-87 48.6 x 109

e- capturePotassium-40 Argon-40 1.4 x 109

MethodIsotope Product Half life

Just How Old is EarthJust How Old is Earth

By modern estimates – about 4.5 billion By modern estimates – about 4.5 billion years oldyears old

How can we tellHow can we tell Remember Science 10 – GeologyRemember Science 10 – Geology Radiometric dating is used to measure Radiometric dating is used to measure

the RADIOACTIVE DECAY of elementsthe RADIOACTIVE DECAY of elements For example…For example…

Aristotle (384-322 BC) proposed spontaneous generation Aristotle (384-322 BC) proposed spontaneous generation living things can arise from nonliving matterliving things can arise from nonliving matter

Leeuwenhoek presented data that seemed to support it Leeuwenhoek presented data that seemed to support it

Spallanzani’s gravy experiments refuted itSpallanzani’s gravy experiments refuted it

Francesco Redi’s ‘s experiments with covered jars refuted Francesco Redi’s ‘s experiments with covered jars refuted it it

Is Spontaneous Generation of Is Spontaneous Generation of Microbial Life Possible?Microbial Life Possible?

Redi’s ExperimentsRedi’s Experiments

Spallanzani’s Gravy ExperimentSpallanzani’s Gravy Experiment

Concluded thatConcluded that Microorganisms exist in air and can Microorganisms exist in air and can

contaminate experimentscontaminate experiments

Spontaneous generation of microorganisms Spontaneous generation of microorganisms does not occurdoes not occur

Critics said sealed vials did not allow Critics said sealed vials did not allow enough air for organisms to survive and enough air for organisms to survive and that prolonged heating destroyed “life that prolonged heating destroyed “life force”force”

Spallanzani’s ExperimentsSpallanzani’s Experiments

Pasteur’s ExperimentsPasteur’s Experiments

Early Earth and the First Early Earth and the First Signs of LifeSigns of Life

Some things to consider…Some things to consider…

Earth was formed ~4,500,000,000 yrs agoEarth was formed ~4,500,000,000 yrs ago

For a few hundred million years Earth was very For a few hundred million years Earth was very hot and constantly bombarded from spacehot and constantly bombarded from space

At this point there was no liquid water, life was At this point there was no liquid water, life was impossibleimpossible

About 3,900,000,000 yrs ago, Earth was About 3,900,000,000 yrs ago, Earth was solidified enough and cool enough for liquid watersolidified enough and cool enough for liquid water

Life apparently arose shortly thereafterLife apparently arose shortly thereafter

More points to ponder…More points to ponder…

What was Earth like 3.9 billion years What was Earth like 3.9 billion years ago?ago? Are there still places on Earth that Are there still places on Earth that

resemble these conditions?resemble these conditions? How could life originally arise from non-How could life originally arise from non-

living matter?living matter? What did it take to form the first life?What did it take to form the first life? What is “life” anyway?What is “life” anyway?

What was earth like 3.9 bya?What was earth like 3.9 bya?

http://www.space.com/scienceastronomy/planetearth/earth_archaean_010716.html

Earth was very different Earth was very different Essentially no Essentially no

atmospheric Oatmospheric O22

Highly corrosive, Highly corrosive, destroys moleculesdestroys molecules

Highly energeticHighly energetic Lightning, volcanic Lightning, volcanic

activity, UV radiation highactivity, UV radiation high Provide energy for Provide energy for

chemical reactionschemical reactions

How could life originally arise How could life originally arise from non-living matter?from non-living matter?

The following hypothesis has been proposed:The following hypothesis has been proposed:

1.1. Non-living synthesis of small organic Non-living synthesis of small organic molecules like amino acids and nucleotidesmolecules like amino acids and nucleotides Plenty of energy availablePlenty of energy available

2.2. Joining of small moleculesJoining of small molecules Proteins and nucleic acidsProteins and nucleic acids

The The Urey-MillerUrey-Miller experiment: experiment:

Abiotic synthesis Abiotic synthesis of organicsof organics

Simulated early EarthSimulated early Earth AtomsphereAtomsphere

H2O, H2, CH4, NH3H2O, H2, CH4, NH3 Simple inorganic moleculesSimple inorganic molecules Electric sparks (lightning)Electric sparks (lightning)

Produced amino acids and other organic moleculesProduced amino acids and other organic molecules Couldn’t happen under modern conditionsCouldn’t happen under modern conditions

Oxidizing atmosphere attacks organic bondsOxidizing atmosphere attacks organic bonds Or: possibly Earth was contaminated with organics from Or: possibly Earth was contaminated with organics from

spacespace

Urey-MillerUrey-Miller

Figure 26.10x LightningFigure 26.10x Lightning

Self AssemblySelf AssemblyLiposomes can “grow” by engulfing smaller Liposomes can “grow” by engulfing smaller

liposomes or “reproduce” by splitting offliposomes or “reproduce” by splitting off

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 26.12a

Where did life originate?Where did life originate?

Shallow water or moist sediments.Shallow water or moist sediments. Deep-sea ventsDeep-sea vents

These sites have energy, produce some These sites have energy, produce some organic compounds, and have inorganic organic compounds, and have inorganic iron and nickel sulfides that can catalyze iron and nickel sulfides that can catalyze some organic reactionssome organic reactions

Deep sea Deep sea ventsvents

Where are they now?Where are they now?

Early life on earth… 3 billion years Early life on earth… 3 billion years of microbesof microbes

Bacteria were the only life for Bacteria were the only life for billionsbillions of years of years

Atmospheric OAtmospheric O22 was first made by was first made by cyanobacteriacyanobacteria Microbes still account for ~half of Microbes still account for ~half of OO22 produced globally produced globally

Plants and animals have only been here for ~600 Plants and animals have only been here for ~600 million yearsmillion years Australopithicus 4 million yrs Australopithicus 4 million yrs Homo sapiens 0.5 million yrsHomo sapiens 0.5 million yrs

Early Earth -- volcanic activity and Early Earth -- volcanic activity and photosynthetic bacteria in dense matsphotosynthetic bacteria in dense mats

Key events in Key events in evolutionary historyevolutionary history

Evolutionary clock: ProkaryotesEvolutionary clock: Prokaryotes

Prokaryotes were the first Prokaryotes were the first organisms on earthorganisms on earth3.5 billion yr old bacterial fossils3.5 billion yr old bacterial fossils Modern filamentous bacteriaModern filamentous bacteria

Cyanobacteria – Very OldCyanobacteria – Very Old

Bacterial mats and StromatolitesBacterial mats and Stromatolites

Fig. 26.4

Stromatolites in Northern CanadaStromatolites in Northern Canada

Atmospheric oxygen began Atmospheric oxygen began accumulating 2.7 billion years agoaccumulating 2.7 billion years ago

Photosynthesis probably Photosynthesis probably evolved very early in evolved very early in bacterial historybacterial history

Cyanobacteria, split water Cyanobacteria, split water and produce Oand produce O22 evolved evolved over 2.7 billion years agoover 2.7 billion years ago

This early oxygen initially This early oxygen initially reacted with dissolved iron reacted with dissolved iron to form the precipitate iron to form the precipitate iron oxide.oxide. Seen today in banded iron Seen today in banded iron

formations.formations.

Banded iron formations -- evidence of oxygen-Banded iron formations -- evidence of oxygen-releasing photosynthesisreleasing photosynthesis

Oxygen accumulationOxygen accumulation ““Corrosive” OCorrosive” O22 had an enormous impact on life, dooming had an enormous impact on life, dooming

many bacterial groupsmany bacterial groups

Some species survived in habitats that remained anaerobic Some species survived in habitats that remained anaerobic (these are “obligate anaerobes”)(these are “obligate anaerobes”)

Other species evolved mechanisms to use OOther species evolved mechanisms to use O22 in cellular in cellular respiration, which uses oxygen to help harvest the respiration, which uses oxygen to help harvest the energy stored in organic moleculesenergy stored in organic molecules

Thus, prokaryotes altered the planet through OThus, prokaryotes altered the planet through O2 2

evolution, making aerobic respiration possible and paving the way for other forms of life (eukaryotes)

Evolutionary clock: EukaryotesEvolutionary clock: Eukaryotes

Evolutionary clock: Multicellular eukaryotesEvolutionary clock: Multicellular eukaryotes

Evolutionary clock: AnimalsEvolutionary clock: Animals

Unnumbered Figure (page 515) Evolutionary clock: Land plantsUnnumbered Figure (page 515) Evolutionary clock: Land plants