The Tree of Life

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Chapter 26

• The Tree of Life An Introduction to Biological
  Diversity

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Overview

• Geologic events that alter environments change
  the course of biological evolution
• Example Large lake splitting into several small
  lakes
• Living things change the planet they inhabit
• Example Evolution of photosynthetic organisms
  putting oxygen into the atmosphere

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Photosynthetic Cyanobacteria
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26.1

• Cells produced in 4 stages
• 1. Abiotic synthesis of AA nucleotides
  (organic compounds)
• 2. Joining of monomers into polymers
• 3. Packaging into protobionts droplets with
  membranes that maintained an internal chemistry
  different from the environment.
• 4. Origin of replication that made inheritance
  possible
• Evidence for each of these 4 stages discussed

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1. Synthesis of organic compounds

• Earth formed about 4.6 billion years ago
• Conditions on early Earth were very different
  from today
• Primitive soup experiment of Miller and Urey
• Strongly reducing atmosphere
• Hydrogen
• Methane
• Ammonia
• Water vapor
• Sparks to mimic lightning

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Conception of Earth 3 billion years ago
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• Extraterrestrial Sources of Organic Compounds
• Amino acids that reached early Earth aboard
  chondrites could have added to the primitive soup
• Looking to other planets for signs of life
• Present day Mars no life
• Billions of years ago it was warm, liquid water,
  and carbon dioxide in the atmosphere

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2. Abiotic synthesis of polymers

• Researchers have produced amino acids polymers by
  dripping solutions of amino acid monomers onto
  hot sand, clay, or rock
• Formed spontaneously

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3. Protobionts

• Replication and metabolism are essential for life
• Protobionts aggregates of abiotically produced
  molecules surrounded by a membrane or
  membrane-like structure.
• Exhibit some properties of life and could have
  formed from abiotically produced organic compounds

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4. Origin of replication

• The first genetic material was probably RNA
• Had the ability to copy itself and began to
  appear in protobionts
• RNA could have been the template on which DNA was
  assembled
• DNA is much more stable and can be replicated
  more accurately so as genomes grew DNA grew
• RNA world gave way to a DNA world and RNA took
  over its role that we see it in today

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26.2 The fossil record

• Fossils are found in sedimentary rocks
• Index fossils the strata at one location can
  often be correlated with strata at another
  location by the presence of similar fossils known
  as index fossils

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Radiometric dating

• Radiometric dating decay of radioactive isotopes
• Half-life the number or years it takes for 50
  of the original sample to decay

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• Carbon-14 has a half life of 5,730 years so it is
  useful for dating fossils up to about 75,000
  years old
• Potassium-40 used to date much older fossils (530
  million years old)
• Magnetism of rocks can also provide dating
  information

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Geologic record

• 3 Eons
• Archaean Proterozoic lasted approx. 4 billion
  years
• These are known as Precambrian
• Phanerozoic eon the last half billion years is
  most of the time multicellular eukaryotic life
  has existed
• Divided into 3 eras
• Paleozoic
• Mesozoic
• Cenozoic
• Boundaries between eras correspond to times of
  mass extinctions seen clearly in the fossil record

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Mass Extinctions

• 2 mass extinctions have received the most
  attention
• Permian Cretaceous
• Permian at the boundary between Paleozoic and
  Mesozoic eras claimed about 96 of marine animal
  speices
• Cretaceous at the boundary between Mesozoic and
  Cenozoic eras doomed more than half of all marine
  species and many families of terrestrial plants
  and animals including the dinosaurs.

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• Permian mass extinction caused by volcanic
  eruptions that increased the carbon dioxide and
  warmed the global climate
• Cretaceous mass extinction caused by an asteroid
  or comet hitting the earth that spewed up dust
  and blocked sunlight for several months.

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Impact Crater
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26.3

• Oldest known fossils
• Date to 3.5 billion years ago
• Stromatolites
• Composed of layers of bacteria and sediment
• Found today in a few warm, shallow, salty bays

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Prokaryotes

• Prokaryotes were Earths sole inhabitants
• 3.5 to about 2 billion years ago

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The oxygen revolution

• Earliest types of photosynthesis did not produce
  oxygen
• Oxygenic photosynthesis evolved 3.5 billion years
  ago in cyanobacteria
• When oxygen started to accumulate in atmosphere
• It posed a challenge for life
• It provided an opportunity to gain abundant
  energy from light
• It provided organisms an opportunity to exploit
  new ecosystems

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26.4 Eukaryotes

• Oldest fossil eukaryotes date back 2.1 billion
  years
• Arose from Endosymbiosis and genetic exchanges
  between prokaryotes
• Endosymbiotic theory states that chloroplasts
  mitochondria were formerly prokaryotic organisms
  living within larger cells.

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Endosymbiosis

• Mitochondria and plastids were formerly small
  prokaryotes living within larger host cells
• Gained entry to the host cell as undigested prey
  or internal parasites
• The host and endosymbionts would have become a
  single organism
• Evidence to support theory
• Similarities in inner membrane structures and
  functions
• Both have their own circular DNA

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26.5 - Multicellularity

• Evolved several times in eukaryotes
• Oldest fossils of eukaryotes, small algae that
  lived 1.2 billion years ago
• 1st multicellular organisms were colonies

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Cambrian Explosion

• Most of the major phyla of animals appear here

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Colonization of land by plants, fungi, and animals

• Occurred about 500 million years ago
• Adaptations that helped prevent dehydration made
  it possible to move out of water onto land
• Symbiotic relationships between plants and fungi
  began at this time and exist today

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Continental Drift

• Continents are not fixed but drift across our
  planets surface on plates of crust that float on
  a hot underlying mantle
• Interactions at plate boundaries
• Convergent boundaries (moving together)
• Divergent boundaries (moving apart)
• Transform boundaries (sliding past one another)
• Volcanoes, Earthquakes, mountain building, and
  subduction occur at plate boundaries

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• The formation and breakup of the supercontinent
  Pangaea explain many biogeographical puzzles
• Land bridges
• Fossils found on 2 continents that cant swim
• Rock formations
• Apparent puzzle piece fit of the continents

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26.6 Taxonomic systems

• Old system was 2 Kingdoms (Plant Animal)
• 5 kingdom system
• Monera, Protists, Plantae, Fungi, Animalia
• 3 Domain system has replaced the 5 kingdom system
• Archaea, Bacteria, Eukarya

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