HISTORY OF LIFE

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HISTORY OF LIFE

• Chapter 14

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Take out notebook paper answer the following
questions with your lab partner

• 1. How old do you think the planet Earth is?
  Explain.
• 2. What physical changes have occurred on Earth
  during its history? What caused these changes?
• 3. What is a Mass Extinction? What evidence do
  scientists have?

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The Record of Life

• Ch. 14 - Section 1 - pg. 369

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Early History of Earth

• 5 billion years ago our solar system was formed
  as a swirling mass of gas and dust
• Gravity pulled this material together to form the
  sun
• Remaining gas and debris circled the newly formed
  sun
• Collisions between the space debris created the
  planets

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• Earth formed about 4.6 billion years ago, dated
  by studying the layers of rock that make up the
  planet
• Young Earth was hot, there was no atmosphere to
  block UV rays from the sun
• No oxygen to breath
• A lot of carbon dioxide and water

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• Life originated in Earths oceans 3.9-3.4 billion
  years ago
• Early life forms would have been very similar to
  bacteria

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Table 14.1 pg. 370

• 4. Which of the following fossil types have you
  or your lab partner seen before? Explain when and
  where.
• Read Paleontologists Detectives to the past on
  pgs. 370 371.
• 5. Give 2 examples of evidence paleontologists
  can use to determine information about the past.
  EXPLAIN!!!

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History in Rocks

• Rocks provide information about Earths history
  including the history of life on Earth
• Paleontologists study ancient life and fossils

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Figure 14.2 pg. 372

• Fossils are found in sedimentary rock
• Organism gets buried in mud, sand, or clay after
  they die
• More sediment gets layered over the organism,
  over time the minerals in the sediment replace
  the minerals in the skeleton

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Figure 14.3 pg. 373

• 6. What are the chances that the Protoceratops
  death was not an accident? Explain your
  reasoning.
• 7. What are 2 ways that the fossil in the Figure
  14.3 could have become exposed?

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Dating Fossils

• Relative Dating (stratigraphy) layers of rocks
  have different ages, the youngest layers on
  top older fossils found in older layers of rock,
  ex. stacks of newspapers.
• Radiometric Dating atoms in the fossil break
  down at a certain rate, age of the fossil depends
  on the ratio of atoms to broken down atoms.

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Geologic Timescale Fig. 14.4 pgs. 374 375

• Begins with the formation of Earth and goes
  through present time
• Scale is divided up by the kinds of organisms
  that lived during that time

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• Layers of rock match up with the Geological
  Timescale

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Organization of the G.T.S.

• 8. List each Era from oldest to most recent and
  describe the types of organism found in each one.
• Broken down into 4 Eras, each era is further
  broken down into Periods.
• The eras and periods are characterized by
  specific events and specific organisms
• Mass Extinction many organisms disappear from
  the GTS almost all at once

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4 Eras

• 1. Precambrian Era
• Beginning of the GTS, longest era, 87 of Earths
  history
• Oldest rocks and fossils are from the Precambrian
  Era
• First organisms were single celled

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• 2. Paleozoic Era
• Cambrian Explosion occurred
• Enormous increase in diversity of life in oceans
• Organisms with backbones emerged
• Mass extinction occurred at the end of the
  Paleozoic Era killing off 90 marine life, 70
  land life

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• 3. Mesozoic Era
• began 248 million years ago
• Dinosaurs died out during another mass extinction
  making room for mammals
• Meteor crash most likely caused the mass
  extinction

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• 4. Cenozoic Era
• Began 65 million years ago
• Increased diversity in mammalian life
• Modern humans appeared 200,000 years ago

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• As you move towards the bottom of the rock
  layers, you move back on the Geological Timescale
• Similar fossils found on different continents
  because at several times in Earths history the
  continents were connected

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Thorium decays into lead. It takes 75,000 years
for half the amount of thorium in a sample to
decay into lead.
Half Life Total years passed Grams of Thorium Grams of Lead
0 0 15 0
1 75,000
2
3
4
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• Pangea existed 250 million years ago
• Plate Tectonics the surface of Earth is made up
  of plates that drift on top of a molten layer of
  rock
• http//www.nature.nps.gov/geology/usgsnps/animate/
  PLATES_3.MPG
• http//www.ucmp.berkeley.edu/geology/tecall1_4.mov

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The Origin of Life

• Ch. 14, Sec. 2

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Spontaneous Generation

• Pre-17th century it was believed that living
  things arose from nonliving things through a
  process called Spontaneous Generation

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• 6th century BC Greek philosophers propose life
  arose when sunlight was shined onto mud. Why?

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• 1600s It was believed that mice appeared from
  rotten grain. Why?

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Francesco Redi (1626-1697)

• Mid-17th century people believed flies were
  spontaneously generated from rotting meat
• Redi was a scientist who noticed a life stage to
  the flies on the rotten meat
• 1. Maggots
• 2. Pupa
• 3. Flies
• He observed that the maggots appeared where flies
  had landed first

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• Redi predicted that if the meat could be kept
  away from the flies, then there would be no
  maggots on the meat
• He did not believe that flies spontaneously
  generated from meat!!!
• So he set up his experiment

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• Control Group uncovered jar of meat, flies
  layed eggs, which hatched into maggots, which
  turned into more flies
• Experimental Group covered jars of meat, flies
  have no chance to lay eggs, new flies do not
  appear

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Louis Pasteur (1822-1895)

• Finally disproved spontaneous generation once and
  for all! 200 years after Redis experiment
• Pasteur set up an experiment where boiled broth
  was exposed to air, but microorganisms couldnt
  fall in

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• By the 1800s scientists understood (thanks to
  the microscope invented a century ago) that
  microorganisms (bacteria viruses) caused people
  to get sick
• But.

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• Some scientists still believed that bacteria and
  viruses spontaneously generated from the air
• Pasteur proved them wrong with his experiment

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• Boiled broth was exposed to air in a specially
  shaped flask over a period of time but nothing
  grew
• Once the neck was broken off bacteria grew in the
  broth
• Bacteria did not spontaneously grow from the
  air!!!

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• Thanks to Pasteur.
• Biogenesis living organisms come from other
  living organisms

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Modern Experiments on Origins

• All elements found in organic compounds needed to
  form biomolecules existed on Earth since its
  formation
• Early atmosphere contained Ammonia (NH3),
  Hydrogen Gas (H2), Water Vapor (H2O), Methane
  (CH4)

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• Under high temperature the gases might have
  formed simple organic compounds (contains Carbon)
  like amino acids
• When Earth began to cool the organic compounds
  would have condensed with the water vapor and
  collected in lakes and seas

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Stanley Miller Harold Urey (1953)

• Recreated the conditions of early Earth in the
  lab on a smaller scale
• Included chemicals present at the time and an
  energy source similar to what as present at the
  time
• Able to generate amino acids (biomolecule)

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Alternative Hypotheses

• 1. Life (biomolecules) emerged in ice (Stanley
  Miller)
• Within ice there are chemicals to create
  biomolecules microscopic pockets of water

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• Water freezes forcing the chemicals to be close
  together which increases the chances of chemical
  reactions occurring
• When the ice melts the biomolecules generated are
  released into oceans

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• 2. Life (biomolecules) emerged in deep sea vents
• Vents provide the heat chemicals that could
  cause chemical reactions to generate biomolecules

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Formation of Protocells

• Protocell Heating the amino acids can cause
  them to take on some life activities like growth
  and division

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First True Cells

• No direct evidence of the first cells, scientist
  can only analyze data that we collect now
• Early Earth had little oxygen, oldest fossils
  thought to be cells resemble the size shape of
  some living prokaryotes, the first cells had
  organic molecules to eat

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• Therefore.
• The first cells were anaerobic, heterotrophic
  prokaryotes
• Anaerobic respiration that doesnt require
  oxygen
• Heterotrophic needs to eat other things in
  order to get the organic molecules needed for
  life

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• Next evolved
• Autotrophs make their own food
• Early autotrophs similar to present day
  Archaebacteria
• Archaea prokaryote organisms that thrive under
  harsh conditions, make food through
  chemosynthesis
• Chemosynthesis CO2 is the carbon source, energy
  comes from the use of inorganic chemicals

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• Next evolved
• Photosynthetic prokaryotes
• Autotrophs now able to use sunlight energy to
  make food
• Created oxygen for the atmosphere which allowed
  for an increase in diversity of life because now
  there was an ozone layer (provides protection
  from UV light)

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Endosymbiotic Theory pg. 385 figure 14.15

• Lynn Margulis hypothesis based on experiments
  and observations
• Proposes that eukaryotes evolved through a
  symbiotic relationship of prokaryotes.
• Ancient prokaryotes engulfed other prokaryotes
  and instead of digesting them they survived
  together.
• Evidence 1.chloroplasts and mitochondria
  contain DNA and ribosomes that are similar to the
  DNA and ribosomes in prokaryotes and unlike DNA
  in eukaryotic cells. 2. Chloroplasts and
  mitochondria reproduce independently of cells
  that contain them.

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• This explains why mitochondria has its own DNA

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Endosymbiosis

• Endosymbiosishttp//highered.mcgraw-hill.com/sites
  /9834092339/student_view0/chapter4/animation_-_end
  osymbiosis.html