AP BIOLOGY THE HISTORY of EARTH

AP BIOLOGYTHE HISTORY of EARTHCHAPTER 25CAMPBELL and REECEConditions on early Earth made the Origin of Life possibleMacroevolution : evolutionary change above the species levelexamples:emergence of terrestrial vertebratesmass extinctions impact on diversity of lifeorigin of key adaptations like flight in birds

Where did 1st cell come from?4 main stages could have produced very simple cells:The abiotic synthesis of small organic moleculesJoining of these small molecules into macromolecules (proteins, nucleic acids)Packaging of these macromolecules into protocells, droplets with membranes that maintained internal chemistry different from their surroundingsOrigin of self-replicating molecules that eventually made inheritance possible

Synthesis of Organic Cpds on early EarthPlanets of our solar system formed ~ 4.6 billion yrs ago1st few hundred million yrs conditions would not have allowed life on Earth

1st AtmosphereCollisions would have vaporized any water preventing seas from formingAtmosphere thick with gases released from volcanic activity

1st Atmosphere1920s: Oparin (Russian chemist) and Haldane (British scientist) each came to conclusion early atmosphere was reducing environment (gain e-) in which organic cpds could have formed from simpler molecules

1st Organic CompoundsEnergy sources:LighteningThermal energyIntense UV radiation

Primordial SoupHaldane had hypothesized the early seas site of 1st organic compounds 1st cellsMiller & Urey (Univ. of Chicago) in 1950s Tested Oparin & Haldane s premiseCreated reducing atmosphereAdded cpds considered to have been there

Miller & Ureys Experiment

Miller & Ureys Results

Miller & Ureys ResultsHave been repeated using same or similar ingredients, different recipes for the atmosphere and they also produced organic compounds

Still ?s about amounts of methane, ammonia (was there really enough to make it a reducing environment?)Some repeated experiment in non-reducing, non-oxidizing conditions & still produce organic cpdsMiller-Urey Experiment demonstrates:Abiotic synthesis of organic molecules is possible under various assumptions about the composition of Earths early atmosphereMeterorites may also have been source of minerals and organic moleculesContain amino acids, lipids, simple sugars, uracil

Murchison Meteorite

Murchison MeteoriteFell to Earth in so named town in Australia in 1969large (100 kg) and was quickly retrieved2010 article published in Scientific American: results of mass spectrometry (separating cpds based on charge & size) have revealed at least 14,000 unique moleculesAbiotic Synthesis of Macromolecules2009 study showed the abiotic synthesis of RNA monomers can occur spontaneously from simpler precursor molecules

Drip solutions with amino acids (aa) or RNA nucleotides onto hot sand, rock, or clay polymers of aa & RNA (w/out using enzymes or ribosomes)ProtocellsBasic characteristics of life : reproduction & metabolism:So 1st cells would have had to be able to reproduce which would have required them to have a source of nitrogenous bases, sugars, phosphate groups Now complex enzymes make this all happen

Vesicles as 1st step?When lipids & other organic molecules added to water vesicles spontaneously formlipid bilayer (separation of hydrophiloic & hydrophobic molecules)These abiotically produced vesicles reproduce and grow on their own.clay like from early Earth will be absorbed into the vesiclessome vesicles demonstrate semi-permeability

Self-Replicating RNARNA can act as enzymeRNA catalysts called: ribozymesSome can make complimentary strands of short pieces of RNA mutations more stable &/or successful

RibozymeOnce self-replicating RNA possible much easier for further changes to happen.Once double-stranded DNA appeared it would have been more stable so RNA left with role we see today

The Fossil Record Documents the History of Life

The Fossil Recordbased mostly on sequence in which fossils have accumulated in sedimentary rock strataan incomplete record of evolutionary change (gaps still be filled in)known fossil record biased toward species that:survived for long periods of timewere abundantwere widespreadin certain types of environmentsmade of some hard parts

This could mess up the fossil record, you know.

Tiktaalikextinctclosest relative to of 1st vertebrate to walk on land

Radiometric DatingMethod of absolute dating based on decay of radioactive isotopes (1 element different element + some particle) Half-life = rate of decay of the specimen lives are constant & characteristic to each radioactive elementoutside conditions do not affect rate of decayDating Fossils C-14in all living thingsC-14 decays into N-14 life = 5,730 yearsmeasure ratio of C-12 to C-14 left in fossilCan only use C-14 dating up to about 75,000 yrs oldamt of C-14 left after that so minimal that accuracy becomes an issue

The 1st Single-Celled Organismsearliest direct evidence of life date from 3.5 billion years ago from fossilized stromatolites

Stromatolitesare layered rocks that form when certain prokaryotes (cyanobacteria) bind thin films of sediment togethertoday, found in warm, shallow salty baysreasonable to infer that the bacteria originated much earlier .. 3.9 billion years ago

StromatolitesEarly prokaryotes were Earths only living inhabitants from 3.5 to 2.1 billion years ago

Photosynthesis & the Oxygen RevolutionMost of Earths atmospheric oxygen is of biologic origin (photosynthesis)at first, O2 would have stayed dissolved in water until concentration high enough to react with Fe in water.Water + iron iron oxide (ppt) these sediment formed banded iron formations

Iron Oxide

OxygenOnce all dissolved Fe ppt out of water the dissolved O2 then released as oxygen gas to atmosphere

Rise of Atmospheric Oxygen

Rise in Atmospheric Oxygenbegan ~2.3 billion years agoWhat caused the rise? probably chloroplastsrising O2 levels would have killed off some anaerobic prokaryotessurvivors in environments with low O2 levelsCellular Respiration may have started as adaptation to rising oxygen 1st Eukaryotesoldest accepted eukaryotic fossils: 2.1 billion years

Endosymbiont Theorymitochondria & plastids (general term for chloroplasts & related organelles) were once prokaryotes that began living in larger host cells

endosymbiont: cell that lives w/in host cellentered cell as undigested prey or internal parasitesymbiotic relationship has been recreated w/in 5 yrs using other cells

symbiosis mutually beneficial

all eukaryotes have mitochondria but not all have plastids soooo

Hypothesis: serial endosymbiosis : mitochondria evolved b/4 plastids

Evidence Supporting Endosymbiosisinner membranes of mitochondria & plastids have enzymes & transport sytems homologous to those found in plasma membranes of living prokaryotesmitochondria & plastids replicate like prokaryoteseach contain a single circular DNA molecule, not assc with histones or large amts other proteins (just like bacterial DNA)

Evidence Supporting Endosymbiosis both have ribosomes & enzymes to transcribe & translate their DNA proteinstheir ribosomes more similar to prokaryotic ribosomes than to eukaryotic cytoplasmic ones

Origin of Multicellularity1st eukaryotes all unicellular organisms

common ancestor of multicellular organisms (based on DNA comparisons) lived ~1.5 billion years ago

Early Multicellular Organisms1st appear in fossil record ~ 575 million yrs agocalled Ediacaran biotasoft bodiedup to 1 m in lengthprobably limitied in size & diversity until late Proterozoic due to series of Ice Ages which covered most of Earths land mass & seas 750 580 million years ago640 million years ago

575 million years agosnowball Earth thawed1st major diversification of multicellular eukaryoteslasted until ~ 40 million years ago

Cambrian Explosion

b/4 Cambrian Explosionall large animals were soft-bodiedlittle evidence of predation

b/4 Cambrian Explosionmany animal phyla began pre-CambrianDNA analysis suggests most animal phyla began to diverge from each other as early as 700 million 1 billion years ago

Colonization of Landfossil evidence of prokaryotes (cyanobacteria & other photosynthetic bacteria) from damp terrestrial surfaces that date well over 1 billion yrs ago500 million yrs ago: fungi, plants, animalsEarly Land PlantAdaptations 420 million Yrs Agointernal vascular system for transporting materials but lacked true rootswaterproofing to slow loss of water to air (no true leaves)

Land Plant Adaptations About 50 million Yrs AgoPlants greatly diversifiedReedsTreelike plants with true roots & leaves

Arthropods & Tetrapodsmost widespread & diverse land animalsarthropods 1st land animals (420 million yrs ago)oldest tetrapods 365 million years ago: ancestor lobe-finned fish

Arthropod Fossils

Early Tetrapods

Human Lineagediverged from other primates 6 7 million yrs agoour species originated ~ 195,000 yrs ago

Plate Tectonics

plates of Earths crust float on underlying mantlemovements in mantle cause plates to move (usually few cm/yr)Plate Boundariesinfluence formation of mtn ranges, islands, earthquakeswhen oceanic plate meets continental plate it is subducted under eventually becoming mantle

Consequences of Continental Driftalters habitats having large impact on living organisms

Pangeaformation would have destroyed a considerable amount of marine life habitat (shallow waters)large land mass would have very dry, cold, severe interiorformation of Pangea would have caused many extinctions but also opened up opportunities for new speciesContinental Drift & Climate Changewhen continent changes location it is bound to change climate200 million yrs ago Labrador, Canada was in the tropics:species had to adapt, move, or become extinct

Effects of Continental Driftpromotes allopatric speciation (formation of new species that are geographically separated from one another) on large scaleas continents drift apart, each becomes a separate evolutionary arena.

Continental Drift Explains Fossil Distributionsame fossils found in Brazil & western Africa

Mass ExtinctionsFossil record shows most species that have ever lived are now extinct.Reasons to become extinct:destroyed habitatchanges in environment that did not favor species

Mass Extinctionscertain times in history environmental changes have caused the normal rate of extinction to increase dramatically = mass extinction5 Big Mass Extinctions5 Mass Extinctions

5 Mass Extinctionsin the past 500 million yearsoccurred with hard-bodied species for which we have a documented fossil recordeach one: 50% or more marine species became extinctMass extinction between Paleozoic & Mesozoic eras claimed ~96% of marine animal species, 8/27 known orders of insects

Permian Mass Extinctiontime of enormous volcanic eruptions in Siberiageologic data indicate 1.6 million km2 covered in hot lava 100s to 1000s m thickMay have produced enough CO2 to warm global climate by 6 C slowed ocean currents drop in [O2 ] ocean anoxia suffocated O2 breathers increased anaerobic bacteria [H2 S] (deadly byproduct) further extinctions on land ozone layer destroyed UV radiation increased more deathCretaceous Mass Extinction~65.5 million yrs agobetween Mezozoic & Cenozoic eras>50% all marine life extincteliminated all dinosaurs (except birds)Reason? Thin layer of clay enriched in iridium lies between sedimentary rock from the 2 eras. Iridium very rare on Earth but common in meteorites

Cretaceaous Mass ExtinctionChicxulub Crater off Yucatan penisula is a 65 million year old scar that could have been caused by hit from a comet or asteroid (crater size indicates hit by something 10 km in diameter)

6th Mass Extinction ?Typical background rate for extinctions is considered to be 1 10 in 400 yrs.There have been > 1,000 extinctions in past 400 yrsNot counting those species (probably some in rain forests) that are becoming extinct that we had never discoveredLosses to date have not reached those of the BIG 5Consequences of Mass Extinctionssignificant & long term effectsextinct species is gone forever course of evolution is changedtakes at least 5-10 million yrs for diversity to recover from a mass extinction

Mass Extinctions & Ecology

Adaptive RadiationsFossil record tells us diversity of life has increased over past 250 million yrsincrease largely due to adaptive radiation: periods of evolutionary change in which groups of organisms form many new species to fill different nichesLarge scale adaptive radiations occurred after each of BIG 5Radiation of Mammalswhen land dinosaurs became extinct 65.5 million yrs ago mammals moved in and filled the ecological roles or niches now available to themoriginal mammals 180 million yrs ago but they remained small, not very diverse, mostly nocturnal,

Development of GenesGenes that control development influence the:rate & timingspatial pattern of change in an organisms form as it develops from zygote adultChange in Rate & TimingHeterochrony : (Gr different, time)an evolutionary change in the rate & timing of developmental eventsHumans relative shape due in part to relative growth rates of different body parts during development

Relative Skull Growth RatesHumans have mutation that slowed growth of jaw relative to other parts of skull produced an adult that looks more similar to chimp fetus than chimp adult

PaedomorphosisAdults of some species retain juvenile features of ancestorsexample: marine salamander axolotl

Changes in Spatial Patternhomeotic genes: master regulatory genes that control placement & spatial organization of body parts in animals

Hox Genes1 class of homeotic genesprovide positional information in animal embryo

Evolution of DevelopmentOrigin of novel morphological forms likely due to new developmental genes arising from gene duplication eventsInsects have crustacean-like ancestors that all have more legs .the Ubx gene is expressed in main trunk of body; in insects it is expressed in abdomen.in crustacean legs .in insects it suppresses leg formationUbx Genemutation Crustacean BodyInsect Body

Changes in Gene RegulationHarmful Changes can be limited to single cell typemay have fewer harmful side effects than point mutations .so less likely to be a lethal changeMarine Stickle back Fish

Lake Stickleback Fish

Evolution is not Goal Orientednew forms arise by slightly modifying existing forms

novel & complex structures can arise as gradual modifications of ancestral structures

each step in process of evolving into something complex would have been useful to the speciesRanges of Eye Complexity among Molluscs

Evolutionary TrendsSpecies Selection Modelproposed by Steven Stanleythinks of species as individuals: speciation is their birth, extinction their deathThe new species that diverge from them are their offspring.The species that last the longest & generate the most new species determine the direction of major evolutionary trends.

Species Selection Model

Evolutionary TrendsNatural Selection still plays a roleexample: ancestors to modern horse were browsers until mid-Cenozoic when grasslands spread across large areas. Horses that were grazers and able to run fastest from predators were selected for