C1.5 - History of Life and Modern Additions to Evolution

PART I: History of Life

The Early Earth

• Characterized by extreme heat, high UV, radio and electrical activity
• Primitive atmosphere contained nitrogen (N₂), carbon dioxide (CO₂), carbon monoxide (CO), ammonia (NH₃), methane (CH₃)
• Asteroid impacts common
• Surface gradually cools, water vapour condenses forming oceans

Miller-Urey Experiment

• First life forms arose by primary abiogenesis theory
• primary abiogenesis theory: theory where life arose from no life
• Complex organic molecules form spontaneously
• organic molecules: molecules that contain carbon
• Miller-Urey experiment recreated early atmosphere
• Sugars, amino acids, and nitrogenous bases created (building blocks of life)
• Thermal proteinoids: protein-like molecules formed abiotically from amino acids

The Oldest Fossils

• 400 my after Earth’s formation: Earth’s crust begins to cool and solidify
• 3.5 bya: life on Earth confirmed
• stromatolites: layered rocks that form when certain prokaryotes bind thin layers of sediment together
• perhaps life in simpler forms began 3.9 bya

Protocells

• All living things composed of cells
• Compartmentalization necessary
• liposomes: lipid membrane
• Lipid membranes form spontaneously
• Membranes may act as semi-permeable barriers

Early Life

• RNA world? No DNA?
• Oldest fossils 3.5B yrs. old
• Oldest life perhaps may have formed in deep sea hydrothermal vents
• Cyanobacteria-like organisms (blue-green)
• Anaerobic and chemoautotrophs
• anaerobic: can break down glucose to energy w/o oxygen
• chemoautotroph: makes own energy through chemical reactions
  • believed that oldest fossilzed prokaryotes evovled from them
• Eukaryotic cells (complex cells w/ nucleus) arise through endosymbiosis
• endosymbiosis: organism that lives within body/cells of another organism

Endosymbiotic Theory

• eukaryotes: cells w/ membrane-bound organelles, nuclei, and complex organelles like mitochondria
• Infolding of membrane formed endoplasmic reticulum and nucleus
• heterotroph: organism that ingests organic carbon to produce energy
• Consumption of heterotrophic cell formed mitochondria
• Consumption of photosynthetic cell formed chloroplasts in plants

The Cambrian Explosion

• Multicellular organisms arise 750 mya
• 565 mya: Animal kingdom undergoes dramatic increase in diversity
• All major animal groups arise in Cambrian explosion
• Early animals preserved in Burgess Shale

Cambrian Explosion illustration

Burgess Shale

Extinction Events

• Geological time divided into 5 eras, subdivided into periods and epochs
• mass extinction: brief episodes of great species loss
• 5 major extinction events
• 65 mya: Cretaceous extinction ends the age of dinosaurs and gives rise to mammals
  • meteor strike near land mass that became Yucatan Peninsula, Mexico
  • polluted sky w/ debris for months
  • dinosaurs thrived on Earth for 150 my
  • all dinos gone, except those that evolved into birds
• end of Permian period
  • 90% of marine animals lost
• pseudoextinction: the species never went extinct, they just evolved
• positive side: adaptive radiation of survivors forming new biodiversity
• 6th great extinction?

Fossil Record and Geologic Time Scale

• geologic time scale: scale that organizes Earth’s geological history into distinct blocks of time
• era: block of time
• period: block formed by dividing era

Continental Drift

• Earth’s continents move on plates floating on hot mantle
• continental drift: movement of continents
  • N.A. and Europe currently drifting apart ~2 cm/yr.
• solution to many biological puzzles
  • i.e. matching Mesozoic fossils in W. Africa and Brazil
  • same fossil in parts of world separated by 3,000 km of ocean?
  • evidence makes sense if part of one land mass during that time
  • explains why life on Australia is so diff. from rest of world

Formation and Breakup of Pangaea

• 250 million years ago, continents formed one landmass called Pangaea (“all land”)
• shorelines reduced, sea levels dropped, shallow seas drained
• many marine habitats destroyed
• inland areas became drier with extreme climates
• species that evolved separately were forced to compete
• led to mass extinctions
• 180 million years ago, Pangaea began breaking apart
• continents drifted and became isolated
• species evolved separately on different land masses
• marsupials survived in isolated Australia
• placental mammals dominated other continents
• explains Australia’s unique marsupial diversity

Phylogeny

Please see Diversity of Life

Human Disruption — Bison Skull Hunting and Processing

Bisons hunted w/ rifles which are accurate and have fairly fast reloads

PART II: Modern Additions to the Evolutionary Theory

Rate of Evolution

• gradualism: evolution of species by gradual accumulation of small genetic changes over a long period of time
  • asserts slow, gradual change
  • small changes accumulate in species over time
  • first developed by Charles Darwin
  • limitation: in fossil record, species would arise abruptly, persist in rock for thousands/mil. of years, then disappear suddenly
• punctuated equilibrium: species often diverge in sudden bursts of rapid evolutionary change
  • developed in 1972 by paleontologists Niles Eldridge and Stephen Jay Gould
  • large changes occur rapidly followed by little change
  • term comes from idea that long periods of little evolutionary changes (equilibrium) are broken (punctuated) by shorter bursts of speciation

FUN FACT: Okapis and giraffes share the same evolutionary common ancestor

Divergent and Convergent Evolution

• divergent evolution: evolution that creates species diverging in similarity
• adaptive radiation: when one species gives rise to many distinct species
  • caused by small founding group colonzing new environment and adapting to its environment over generations
  • the new group changes and loses compatibility with original group
• convergent evolution: distantly-related species develop similar adaptations, “analogous structures”

Co-Evolution and Mimicry

• co-evolution: one species evolves in response to another species’ evolutionary changes
• mutualism: when two species support each other in order to survive
  • i.e. flowers and insects have a mutual relationship w/ each other; insects get food and flowers get pollinated
• Plants evolved toxins to prevent insects from eating them, but insects also evolved to resist these toxins to eat them again
  • i.e. milkweed plants produce toxins, but monarch caterpillar can handle toxins and store them so that they aren’t eaten
• mimicry: one species evolves to represent another species to gain a survival advantage
  • i.e. hoverfly looks like a wasp, and predators avoid both to avoid a poisonous sting

Sources

• Mr. C. Jones
• BiologySource 11