14-2: EARTH’S HISTORY

The Formation of EarthThe Formation of Earth►About 5 billion years ago, our solar About 5 billion years ago, our solar

system was a swirling mass of gas and system was a swirling mass of gas and dustdust

►Over time, these materials collapsed Over time, these materials collapsed inward forming the suninward forming the sun

Formation (cont.)Formation (cont.)►The planets are The planets are thought to have been thought to have been

made from 400 million years of made from 400 million years of constant collisions of dust and debrisconstant collisions of dust and debris

►Earth grew from these collisionsEarth grew from these collisions Thermal energy was released each time Thermal energy was released each time

debris hit the Earthdebris hit the Earth

Earth’s AgeEarth’s Age►Earth is more than 4 Earth is more than 4

billion years old billion years old (~4.6 b.y.)(~4.6 b.y.)

►How do we know?How do we know? Scientists have Scientists have

drilled holes down drilled holes down into Earth’s layersinto Earth’s layers

More modern More modern techniques techniques established in the established in the 2020thth century century

Radiometric DatingRadiometric Dating► A A radioactive isotope radioactive isotope is used to date materialis used to date material► The isotope is chemically unstableThe isotope is chemically unstable

Nucleus will release particles/radiant energyNucleus will release particles/radiant energy Known as Known as radioactive decayradioactive decay

► Scientists will measure the Scientists will measure the half-lifehalf-life of a of a radioactive isotoperadioactive isotope Length of time it takes for ½ of the isotope to decayLength of time it takes for ½ of the isotope to decay Half-lives vary from fraction of a second to billions of Half-lives vary from fraction of a second to billions of

yearsyears

Half-live GraphHalf-live Graph

Example:Example: C-14 C-14 DatingDating► Organic materials can Organic materials can

be dated by comparing be dated by comparing the amount of the amount of C-14C-14::C-C-1212

► Living things take Living things take carbon into their bodies carbon into their bodies constantly, most of it in constantly, most of it in the form of the form of C-12C-12; a very ; a very small proportion of it is small proportion of it is C-14C-14, which undergoes , which undergoes decaydecay

Example: C-14 DatingExample: C-14 Dating► When an organism dies, its uptake of carbon When an organism dies, its uptake of carbon

STOPSSTOPS, and decay of the existing , and decay of the existing C-14C-14 continues continues► Thus over time, the amount of Thus over time, the amount of C-14C-14 declines with declines with

respect to the original amount of stable respect to the original amount of stable C-12C-12► The half-life of The half-life of C-14C-14 is 5,730 years is 5,730 years

C-14C-14 is limited to organic remains less than 60,000 years is limited to organic remains less than 60,000 years oldold

Radiometric Dating (cont.)Radiometric Dating (cont.)►The two isotopes that were used to The two isotopes that were used to

date the Earth were:date the Earth were: Thorium-230 (75,000 years)Thorium-230 (75,000 years) Uranium-238 (4.5 billion yrs)Uranium-238 (4.5 billion yrs)

►Scientists found rocks + zircon crystals Scientists found rocks + zircon crystals that are 4.2 billion years old - - so that are 4.2 billion years old - - so Earth must be older than thatEarth must be older than that

The First Organic CompoundsThe First Organic Compounds►All of the elements in All of the elements in organic organic

compounds compounds were thought to have were thought to have existed on Earth and in the solar existed on Earth and in the solar system when Earth formedsystem when Earth formed

►How did all these elements assemble How did all these elements assemble into life forms?into life forms?

Alexander I. OparinAlexander I. Oparin► In 1923, Oparin + HaldaneIn 1923, Oparin + Haldane

““Primordial SoupPrimordial Soup” model” model►Spontaneous origin from inorganic gasesSpontaneous origin from inorganic gases

►They believed the atmosphere They believed the atmosphere contained:contained: Ammonia – NHAmmonia – NH33

Hydrogen gas – HHydrogen gas – H22

Water vapor – HWater vapor – H22OO

Methane gas – CHMethane gas – CH44

Oparin (cont.)Oparin (cont.)► At high temps, these gases might At high temps, these gases might

have formed org. comps such as have formed org. comps such as amino acidsamino acids

►When the Earth When the Earth cooledcooled, water , water condensed to form lakes and seascondensed to form lakes and seas compounds collected in watercompounds collected in water over time, entered chemical over time, entered chemical

reactions = fueled by reactions = fueled by lightninglightning + + UV UV radiationradiation

► These rxns could have ultimately These rxns could have ultimately resulted in macromolecules resulted in macromolecules essential to life such as essential to life such as PROTEINSPROTEINS; building blocks for ; building blocks for the 1the 1stst cells cells

Synthesis of Org. CompoundsSynthesis of Org. Compounds►Oparin never tested Oparin never tested

his hypothesishis hypothesis► In 1953, Miller + In 1953, Miller +

Urey tested Urey tested Oparin’s hypothesisOparin’s hypothesis Set-up this Set-up this

apparatusapparatus

Miller-Urey (cont.)Miller-Urey (cont.)►Experiment:Experiment:

Chamber with gases Chamber with gases Oparin thought were on Oparin thought were on early Earthearly Earth

Simulated lightning Simulated lightning (spark from electrode)(spark from electrode)

Chemical reactionsChemical reactions Produced a variety of Produced a variety of

organic compounds, organic compounds, including AAincluding AA

Miller-Urey (cont.)Miller-Urey (cont.)

►Since the 1950s, scientists have Since the 1950s, scientists have continued to explore this idea of continued to explore this idea of spontaneous originspontaneous origin Have been able to produce AA, ATP, and Have been able to produce AA, ATP, and

DNA nucleotidesDNA nucleotides

►Suggests that there were many ways Suggests that there were many ways these compounds could have formed these compounds could have formed on young Earthon young Earth

Miller-Urey (cont.)Miller-Urey (cont.)► In more recent years, new In more recent years, new

hypotheses were proposed as to hypotheses were proposed as to the atmosphere on early Earththe atmosphere on early Earth

► The gases included:The gases included: Carbon dioxide – COCarbon dioxide – CO22

Nitrogen – NNitrogen – N22

Water vapor – HWater vapor – H22OO

► Lab simulations showed the COLab simulations showed the CO22 + O+ O22 interfere with production interfere with production of organic compoundsof organic compounds Organic compounds might Organic compounds might

have only been able to be have only been able to be produced in protected areas produced in protected areas from the atmosphere…from the atmosphere…

► Under Under WATERWATER??????

Org. Compounds beyond Org. Compounds beyond EarthEarth

►Another Hypothesis…Another Hypothesis… The organic compounds could have been The organic compounds could have been

carried to Earth by debris from space carried to Earth by debris from space (meteorite)(meteorite)

Scientists hypothesized that these Scientists hypothesized that these compounds were formed in space and could compounds were formed in space and could have accumulated on Earth’s surfacehave accumulated on Earth’s surface

From Molecules to Cell-like From Molecules to Cell-like StructuresStructures► Scientists (Scientists (Sidney FoxSidney Fox) have tried to ) have tried to

create the physical structures that create the physical structures that may have given rise to the first cellsmay have given rise to the first cells These cell-like structures were created These cell-like structures were created

in a lab from simple organic compoundsin a lab from simple organic compounds

Microspheres Microspheres ►Spherical in shapeSpherical in shape►Composed of many protein molecules Composed of many protein molecules

organized in a membraneorganized in a membrane

CoacervatesCoacervates►Collection of droplets from dissimilar Collection of droplets from dissimilar

substances (AA + sugars)substances (AA + sugars)

From Molecules to Cell-like StructuresFrom Molecules to Cell-like Structures► For many years, it had been assumed that all For many years, it had been assumed that all

cell structures and the chemical reactions of cell structures and the chemical reactions of life required life required ENZYMESENZYMES that were specified by that were specified by the genetic information of the cellthe genetic information of the cell

► Both microspheres and coacervates were Both microspheres and coacervates were spontaneously created in a lab and have spontaneously created in a lab and have several life-like properties, such as several life-like properties, such as growth, growth, reproduction, + taking in substances from reproduction, + taking in substances from their environmenttheir environment

►Microspheres + coacervates do not have Microspheres + coacervates do not have hereditaryhereditary characteristicscharacteristics and thus aren’t and thus aren’t LIVINGLIVING!!