Ch. 25 – Ch. 25 – The The

History History of Life of Life

on Earthon Earth

Lost WorldsLost Worlds

Macroevolution• Broad pattern of

evolution above the species levels

• Terrestrial vertebrates

• Mass extinctions• Origin of key

adaptations

Early EarthEarly Earth3.5 billion year old fossils4 main stages:1. Abiotic synthesis of small organic

molecules2. Joins of the small molecules into

macromolecules• Abiotic synthesis of RNA

monomers3. Packaging of molecules into

protocells• Reproduction and metabolism

must be carried out simultaneously

• Vesicles4. Origin of self-replicating molecules

that eventually lead to inheritance• ribozymes

Fossil RecordFossil Record Sedimentary rocks• richest source of fossilsGreat changes in the

kinds of organisms on Earth at different points in time

• Incomplete chronicleDating fossils• relative dating

– compare strata– only relative

• Radiometric dating – assign age in yrs.– Based on radioisotopes

and half life

Fossil RecordFossil Record • Substantial chronicle of

evidence• Phylogeny has a

biogeographical basis in continental drift– spatial distribution of

life• Mammals

– Tetrapods– Mandible bone– Middle ear bones– Mammalian’s teeth

Origin of Single-celled and Multicelled Origin of Single-celled and Multicelled Organisms and Colonization of the LandOrganisms and Colonization of the Land

Geologic record• Three eons

– Archaean– Protozoic– Phanerozoic

•Paleozoic•Mesozoic•Cenozoic

First single celled organisms• Two rich sources for early prokaryote fossils are

stromatolites (fossilized layered microbial mats) and sediments from ancient hydrothermal vent habitats.

• 3.5 billion years ago• Found today in warm, salty bays

Fig. 26.4

• Recent fossil finds from China have produced a diversity of algae and animals from 570 million years ago, including beautifully preserved embryos (SEM).

Fig. 26.7

Photosynthesis and the Oxygen RevolutionPhotosynthesis and the Oxygen Revolution

Oxygen gas• Produced from

photosynthesisFirst Eukaryotes• 2.1 billion years old• Endosymbiotic theory• Serial endosymbiosis

Origin of MulticellularityOrigin of Multicellularity

1.5 billion years agoWhy were they limited

in size until about 535 million years ago?

• Severe ice agesCambrian explosionColonization of Land• 500 million years ago

Speciation and Speciation and Extinction RatesExtinction Rates

Plate Tectonics• Continental drift

Speciation and Speciation and Extinction RatesExtinction Rates

Mass Extinctions

• “Big Five” Mass Extinction Events

Speciation and Speciation and Extinction RatesExtinction RatesAdaptive

Radiations• Occurred

after each mass extinction

• Worldwide• Regional

Major Changes in Body Form can Result Major Changes in Body Form can Result from Changes in the Sequences and from Changes in the Sequences and Regulation of Developmental GenesRegulation of Developmental Genes

Heterochrony• Evolutionary

change in the rate or timing of developmental events

Major Changes in Body Form can Result Major Changes in Body Form can Result from Changes in the Sequences and from Changes in the Sequences and Regulation of Developmental GenesRegulation of Developmental Genes

Paedomorphosis• Sexually mature

features may be retained from juvenile structures

Major Changes in Body Form can Result from Major Changes in Body Form can Result from Changes in the Sequences and Regulation of Changes in the Sequences and Regulation of

Developmental GenesDevelopmental Genes

Homeotic genes• Master

regulatory genes• Control the

placement and spatial organization of body parts

• Hox genes– Provide

positional information in an animal embryo

Major Changes in Body Form can Result from Major Changes in Body Form can Result from Changes in the Sequences and Regulation of Changes in the Sequences and Regulation of

Developmental GenesDevelopmental Genes

Evolution of Development• Changes in genes• Changes in gene regulation

Evolution is NOT Goal OrientedEvolution is NOT Goal Oriented

Evolutionary novelties

• Eye– Patch of

pigmented cells– Eyecup– Camera type eye– Eye with

primitive lens– Complex camera

lens-type eye– Still maintain

function of vision

• Exaptations

Evolution is NOT Goal OrientedEvolution is NOT Goal Oriented

Evolutionary Trends• Evolution of the

horseResult of

interactions between organisms and their current environments

• If environment changes trend may cease or reverse