Chapter 17Chapter 17

The Origin of LifeThe Origin of Life

17.1 The Big Bang17.1 The Big Bang

Evidence indicates that 15 billion Evidence indicates that 15 billion years ago, Universe = one big years ago, Universe = one big supermass that explodedsupermass that exploded

Explosion of the supermass – “Big Explosion of the supermass – “Big Bang” – hurled matter & energy Bang” – hurled matter & energy into space & then pulled together into space & then pulled together into clumps (stars, galaxies, into clumps (stars, galaxies, planets, etc)planets, etc)

17.1 The Big Bang17.1 The Big Bang

Age of Earth = ~ 4.6 billion years Age of Earth = ~ 4.6 billion years oldold

17.2 Early Earth17.2 Early Earth

Early atmosphere = very hot, Early atmosphere = very hot, composed of volcanic gasses – composed of volcanic gasses – nitrogen, hydrogen, carbon nitrogen, hydrogen, carbon monoxide, carbon dioxide, & monoxide, carbon dioxide, & water vaporwater vapor

It’s believed there was NO It’s believed there was NO OxygenOxygen

17.2 Early Earth17.2 Early Earth

OO22 accumulated in atmosphere ~ accumulated in atmosphere ~ 2.5 billion years ago2.5 billion years ago

When photosynthesizers started When photosynthesizers started to produce Oto produce O22 as a waste product as a waste product

OO22 reached modern levels about reached modern levels about 360 million years ago360 million years ago

17.3 The Beginnings of 17.3 The Beginnings of LifeLife Reasons why Earth was hostile to Reasons why Earth was hostile to

living things:living things:

– Volatile (very reactive) gassesVolatile (very reactive) gasses– UV radiation would have damaged UV radiation would have damaged

DNADNA

17.3 The Beginnings of 17.3 The Beginnings of LifeLife

3 Popular scientific explanations 3 Popular scientific explanations for the origin of life:for the origin of life:– Life originated on some planet & Life originated on some planet &

traveled to Earth through spacetraveled to Earth through space– Life originated by unknown means on Life originated by unknown means on

EarthEarth– Life evolved from nonliving Life evolved from nonliving

substances through interaction with substances through interaction with the enviormentthe enviorment

17.3 The Beginnings of 17.3 The Beginnings of LifeLife Other explanations (supernatural Other explanations (supernatural

forces or a deity) aren’t within forces or a deity) aren’t within scope of science because we scope of science because we can’t use science to confirm or can’t use science to confirm or reject itreject it

Oparin-HaldaneOparin-Haldane

Environmental energies Environmental energies (radiation, lightning, & heat) (radiation, lightning, & heat) provided the energy needed to provided the energy needed to cause atmospheric gases to form cause atmospheric gases to form organic compoundsorganic compounds

The organic compounds formed a The organic compounds formed a “primordial soup”“primordial soup”

Oparin-HaldaneOparin-Haldane

Both believed 1st life forms fed Both believed 1st life forms fed on the “soup” = heterotrophson the “soup” = heterotrophs

Heterotroph Hypothesis:Heterotroph Hypothesis:– Need a supply of organic molecules Need a supply of organic molecules

produced by nonbiological sourcesproduced by nonbiological sources– Processes had to create polymers Processes had to create polymers

from the small organic moleculesfrom the small organic molecules– Processes had to organize the Processes had to organize the

polymers so they could self-replicatepolymers so they could self-replicate

Miller & UreyMiller & Urey

Is it possible to make organic Is it possible to make organic compounds from inorganic compounds from inorganic compounds?compounds?

Built an apparatus in a lab that Built an apparatus in a lab that simulated early atmosphere - added simulated early atmosphere - added all the gasses that were present all the gasses that were present (methane, ammonia, water vapor, (methane, ammonia, water vapor, hydrogen), a spark = lightning, a hydrogen), a spark = lightning, a condenser = rain to cool gassescondenser = rain to cool gasses

Miller & UreyMiller & Urey

Able to accumulate a liquid Able to accumulate a liquid containing organic molecules = containing organic molecules = amino acids & with some changes amino acids & with some changes bases and ribose sugarbases and ribose sugar

Miller & UreyMiller & Urey

A.G. Cairns-SmithA.G. Cairns-Smith Hypothesized that clay particles Hypothesized that clay particles

helped catalyze the first polymershelped catalyze the first polymers Clay = repeating crystal structures Clay = repeating crystal structures

that can attract certain molecules that can attract certain molecules like amino acidslike amino acids

The crystals could have then The crystals could have then catalyzed the bonding between catalyzed the bonding between these to form polymersthese to form polymers

We are still left with many We are still left with many questions but we have a possibilityquestions but we have a possibility

““Chicken & the Egg”Chicken & the Egg”

Self-replication = chicken & the egg Self-replication = chicken & the egg problemproblem

DNA = universal information DNA = universal information molecule for life on Earth molecule for life on Earth

Replication of DNA requires proteins Replication of DNA requires proteins but proteins are coded for by DNAbut proteins are coded for by DNA

Seems impossible to make proteins Seems impossible to make proteins without DNA & DNA without proteinswithout DNA & DNA without proteins

Possible Solution to Possible Solution to Chicken & the EggChicken & the Egg RNA-world Hypothesis RNA-world Hypothesis

Components of RNA can be produced Components of RNA can be produced from inorganic compounds & can from inorganic compounds & can join spontaneously and some can join spontaneously and some can catalyze their own partial replicationcatalyze their own partial replication

RNA served as the 1st information RNA served as the 1st information molecule & the catalystmolecule & the catalyst

17.5 Biological 17.5 Biological EvolutionEvolution NASA’s definition of life:NASA’s definition of life:

– A self-sustained chemical system A self-sustained chemical system that is capable of undergoing that is capable of undergoing Darwinian or biological evolutionDarwinian or biological evolution

– Origin of life = beginning of Origin of life = beginning of biological evolutionbiological evolution

17.5 Biological 17.5 Biological EvolutionEvolution 3 processes needed for biologial 3 processes needed for biologial

evolution:evolution:– Self-reproductionSelf-reproduction– Inheritable mutationsInheritable mutations– Natural selectionNatural selection

17.5 Biological 17.5 Biological EvolutionEvolution Cell theory = all life is made of Cell theory = all life is made of

cells, so how did cells arise?cells, so how did cells arise? To get a cell, we need a cell To get a cell, we need a cell

membrane (to separate it from membrane (to separate it from the outside)the outside)

Still not clearly understood where Still not clearly understood where cells & their membranes came cells & their membranes came fromfrom

17.5 Biological 17.5 Biological EvolutionEvolution Carl Woese proposed a model for Carl Woese proposed a model for

formation of 1st cellsformation of 1st cells Cells formed with the help of the Cells formed with the help of the

“greenhouse effect” produced by “greenhouse effect” produced by carbon dioxide; meteors hit earth carbon dioxide; meteors hit earth creating large amount of dust creating large amount of dust which got covered with water which got covered with water dropletsdroplets

17.5 Biological 17.5 Biological EvolutionEvolution The droplets were warmed by the The droplets were warmed by the

atmosphere & acted like the first atmosphere & acted like the first cells in which reactions could cells in which reactions could occuroccur

17.7 Eukaryotes17.7 Eukaryotes

First life = prokaryotes, ~3.5 First life = prokaryotes, ~3.5 billion years oldbillion years old

Endosymbiont Theory (Margulis)Endosymbiont Theory (Margulis)– SymbiosisSymbiosis – an ecological – an ecological

relationship between organisms of relationship between organisms of two species that live together in two species that live together in direct contactdirect contact

17.7 Eukaryotes17.7 Eukaryotes

Endosymbiont Theory (Margulis)Endosymbiont Theory (Margulis)– Margulis proposed that eukaryotes Margulis proposed that eukaryotes

began from a symbiosis between a began from a symbiosis between a large anaerobic prokaryote and a large anaerobic prokaryote and a smaller aerobic or photosynthetic smaller aerobic or photosynthetic prokaryote.prokaryote.

– The large cell absorbed the smaller The large cell absorbed the smaller one & the smaller cell survived one & the smaller cell survived within the host (eventually becoming within the host (eventually becoming a mitochondrion or chloroplast)a mitochondrion or chloroplast)

17.7 Eukaryotes17.7 Eukaryotes Endosymbiont Theory (Margulis)Endosymbiont Theory (Margulis)

– The The endosymbiontsendosymbionts (internal (internal partners) lost the ability to live partners) lost the ability to live independentlyindependently