The History of The History of LifeLife

Chapter 14Chapter 14

Early EarthEarly Earth

Was Was inhospitableinhospitable! ! Very Very hothot due to: due to:

Meteoric impactMeteoric impact Volcanic eruptionsVolcanic eruptions Radioactive decayRadioactive decay

Early atmosphere Early atmosphere contained:contained: Mostly Mostly water vaporwater vapor, ,

nitrogennitrogen, and , and carbon carbon dioxidedioxide

Almost Almost no oxygenno oxygen..

Early Earth TimelineEarly Earth Timeline

~4.6 bya~4.6 bya: Formation of the Earth: Formation of the Earth ~4.5 bya: Formation of the moon~4.5 bya: Formation of the moon ~4.0 bya: Earth begins to cool~4.0 bya: Earth begins to cool ~3.9~3.9 bya: bya:

Oldest rocksOldest rocks Primordial oceans begin to formPrimordial oceans begin to form

~3.8 bya~3.8 bya: First prokaryotic organisms: First prokaryotic organisms ~2.5 bya: First stable continents~2.5 bya: First stable continents ~2.1 bya~2.1 bya: First eukaryotic organisms: First eukaryotic organisms

FossilsFossils

Over Over 99%99% of the of the organisms that organisms that have ever lived have ever lived on this Earth are on this Earth are now now extinctextinct!!!!

We know about We know about these organisms these organisms by by impressionsimpressions left in rocks, left in rocks, amber and ice.amber and ice.

Dating TechniquesDating Techniques

RelativeRelative Dating Dating Places items in sequencePlaces items in sequence No exact date is assignedNo exact date is assigned

NumericNumeric Dating Dating Provides an actual dateProvides an actual date Radioactive Dating: utilizes radioactive Radioactive Dating: utilizes radioactive

isotopes of elements.isotopes of elements.

Geologic Time ScaleGeologic Time Scale

Early Theories on the Early Theories on the Origin of LifeOrigin of Life

Spontaneous GenerationSpontaneous Generation Idea that nonliving material can Idea that nonliving material can

produce lifeproduce life Example: Rotting meat produces flies Example: Rotting meat produces flies

BiogenesisBiogenesis Idea that living organisms must come Idea that living organisms must come

from other living organisms.from other living organisms.

Spontaneous GenerationSpontaneous Generation

Italian scientist, Italian scientist, Francisco Redi,Francisco Redi, disproved the myth, but only for disproved the myth, but only for largerlarger organisms. organisms.

BiogenesisBiogenesis

But scientists still believed that But scientists still believed that maybe maybe microorganismsmicroorganisms arose arose spontaneously from the air.spontaneously from the air.

French scientist, French scientist, Louis PasteurLouis Pasteur, , finally disproved spontaneous finally disproved spontaneous generation by designing an generation by designing an experiment where experiment where airair but no but no organisms were allowed to contact a organisms were allowed to contact a nutrient broth…nutrient broth…nothing grew!nothing grew!

Pasteur’s Pasteur’s ExperimentExperiment

Modern TheoriesModern Theories

Two developments must have Two developments must have preceded life on Earthpreceded life on Earth Formation of organic (carbon-Formation of organic (carbon-

containing) moleculescontaining) molecules Formation of protocells (early cells)Formation of protocells (early cells)

Formation of Organic Formation of Organic MoleculesMolecules

Simple organic molecules (Simple organic molecules (carboncarbon containing) must have formed containing) must have formed

These molecules must have organized These molecules must have organized into more complex molecules like into more complex molecules like proteinsproteins, , carbohydratescarbohydrates, , lipidslipids and and nucleic acidsnucleic acids..

In 1930, Russian scientist, In 1930, Russian scientist, Alexander Alexander OparinOparin, hypothesized life began in , hypothesized life began in oceansoceans by chemical reactions with the by chemical reactions with the atmosphere, atmosphere, lightninglightning, and Earth’s heat , and Earth’s heat to produce organic molecules.to produce organic molecules.

Primordial Soup TheoryPrimordial Soup Theory Developed by Alexander Oparin. Developed by Alexander Oparin. Earth’s ancient atmosphere probably Earth’s ancient atmosphere probably

contained nitrogen, methane, and ammonia contained nitrogen, methane, and ammonia gases, but little to no oxygen.gases, but little to no oxygen.

Energy from sun fueled chemical reactions Energy from sun fueled chemical reactions in the atmosphere forming organic in the atmosphere forming organic molecules (Carbon based molecules) like molecules (Carbon based molecules) like amino acidsamino acids

These molecules were then washed into the These molecules were then washed into the oceans making a primordial soup of organic oceans making a primordial soup of organic moleculesmolecules

Eventually these proteins, lipids, and other Eventually these proteins, lipids, and other organic molecules formed the first cells.organic molecules formed the first cells.

Miller and Urey’s Miller and Urey’s ExperimentExperiment

In 1953, American In 1953, American scientists, Stanley scientists, Stanley Miller and Harold Miller and Harold Urey tested Urey tested Oparin’s Oparin’s hypothesis.hypothesis.

Their result was Their result was the formation of the formation of amino acidsamino acids, , sugarssugars and other and other simple organic simple organic molecules.molecules.

This This supportedsupported Oparin’s Oparin’s hypothesis.hypothesis.

Formation of ProtocellsFormation of Protocells Various experiments during the 1950’s Various experiments during the 1950’s

showed how showed how complexcomplex organic molecules organic molecules might have formed from small organic might have formed from small organic molecules in pools of heated water.molecules in pools of heated water.

American scientist, American scientist, Sidney FoxSidney Fox, , provided a mechanism to explain the provided a mechanism to explain the formation of formation of protocellsprotocells. .

A protocell is a large, ordered structure, A protocell is a large, ordered structure, enclosed by a membrane, that carries enclosed by a membrane, that carries out some life activities such as out some life activities such as growthgrowth and and divisiondivision..

Evolution of the CellEvolution of the Cell

First cells were First cells were prokaryotesprokaryotes that that may have evolved from protocells.may have evolved from protocells.

They were They were anaerobicanaerobic organisms, organisms, meaning they lived in the absence of meaning they lived in the absence of oxygen.oxygen.

They were also They were also heterotrophsheterotrophs, , meaning they obtained food rather meaning they obtained food rather than making it themselves.than making it themselves.

First AutotrophsFirst Autotrophs AutoAuto means means selfself ; ; trophtroph

means means energyenergy Were probably similar to Were probably similar to

today’s today’s archaebacteriaarchaebacteria: : prokaryotic prokaryotic chemosyntheticchemosynthetic organisms found in organisms found in harshharsh conditions such as deep sea conditions such as deep sea vents.vents.

Chemosynthesis is the Chemosynthesis is the process of releasing energy process of releasing energy from from inorganicinorganic compounds compounds such as Hsuch as H22S.S.

First Photosynthetic First Photosynthetic OrganismsOrganisms

Are responsible for the first atmospheric Are responsible for the first atmospheric oxygenoxygen..

Were also Were also prokaryotesprokaryotes.. Also responsible for the Also responsible for the ozoneozone layer. layer.

The ozone layer provided The ozone layer provided protectionprotection against against high energy radiation such as UV and high energy radiation such as UV and gamma rays. gamma rays.

This allowed organisms to move on to This allowed organisms to move on to landland.. This allowed for more This allowed for more aerobicaerobic organisms. organisms.

EndosymbiontEndosymbiont Theory Theory Proposed in the 1960’s by American Proposed in the 1960’s by American

biologist, biologist, Lynn MargulisLynn Margulis.. Explains how Explains how eukaryoticeukaryotic cells may have cells may have

arisen.arisen. States that:States that:

Mitochondria Mitochondria and and chloroplastschloroplasts were actually were actually once prokaryotic cells. (They both have their once prokaryotic cells. (They both have their own own DNADNA similar to prokaryotic DNA.) similar to prokaryotic DNA.)

A cell ingested these bacteria and the A cell ingested these bacteria and the bacteria were protected while providing bacteria were protected while providing energyenergy for the cell. Eventually the bacteria for the cell. Eventually the bacteria could no longer live on their own, and the could no longer live on their own, and the eukaryotic cell evolved. eukaryotic cell evolved.