ch. 17 the history of life
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Ch. 17 The History of Life. 17.1 How Did Life Begin? 17.2 What Were the Earliest Organisms Like?. 17-1 How Did Life Begin?. A. Pre-Darwinian thought held that all species were simultaneously created by God a few thousand years ago - PowerPoint PPT PresentationTRANSCRIPT
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Ch. 17 Ch. 17 The History of The History of LifeLife
17.1 How Did Life Begin?17.1 How Did Life Begin?
17.2 What Were the Earliest 17.2 What Were the Earliest
Organisms Like?Organisms Like?
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17-1 How Did Life Begin?17-1 How Did Life Begin?
A. Pre-Darwinian thought held that all species were simultaneously created by God a few thousand years ago
B. Until 19th century, most people believed in spontaneous generation (abiogenesis) where new organisms sprang up from both non-living matter.
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17-1 How Did Life Begin?17-1 How Did Life Begin?• Spontaneous generation advocates believed
– Maggots were thought to arise from decaying meat– Microbes were thought to arise from broth– Mice were thought to arise from mixtures of sweaty
shirts and wheat
• Francesco Redi (1668) disproved maggots-from-meat idea– No maggots developed when he kept flies away
from uncontaminated meat
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17-1 How Did Life Begin17-1 How Did Life Begin??
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17.1 How Did Life Begin17.1 How Did Life Begin
• Louis Pasteur and John Tyndall (mid 1800s) disproved broth-to-microorganisms idea
– Microorganisms didn’t appear in the sterile broth unless the broth was 1st exposed to existing microorganisms
– Experiment demolished the notion of spontaneous generation but didn’t address how life on Earth originated in the first place
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17.1 How Did Life Begin17.1 How Did Life Begin
The broth in a flask is boiled to kill preexisting
microorganisms
The long, S-shaped neckallows air, but not microorganisms
to enter the flask
If the neck is later broken off, outside air can carry
microorganisms into the broth
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• Alexander Oparin and John Haldane showed that spontaneous generation formation of complex organic molecules necessary for life would NOT be permitted in today’s oxygen-rich atmosphere
• Oxygen reacts with other molecules breaking chemical bonds
• An oxygen-rich environment tends to keep molecules simple
17.1 How Did Life Begin17.1 How Did Life Beginhttp://education-portal.com/academy/lesson/the-origin-of-life-on-earth-theories-and-explanations.html#lesson (good intro to Primordial soup and Oparin and Mill-Urey Exp)
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ammonia (NH3) hydrogen gas (H2) water vapor (H2O) methane gas (CH4)
EARLY EARTH CONDITIONS
high temperatures frequent volcanoes electrical storms comets
17.1 How Did Life Begin17.1 How Did Life Begin
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• The first living things arose from non-living ones– Organic molecules can form spontaneously under
prebiotic (before life) conditions
– Stanley Miller and Harold Urey (1953) designed an experiment that simulated prebiotic evolution
– http://www.ucsd.tv/miller-urey (online Miller-Urey Activity)
• Simulated early Earth’s atmosphere by mixing the gases in a flask and adding an electrical charge (simulate lightening)
17.1 How Did Life Begin17.1 How Did Life Begin
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Urey-Miller Experimental ApparatusUrey-Miller Experimental Apparatus
17.1 How Did Life Begin17.1 How Did Life Begin
• Simple organic molecules appeared in just a few days
• Small molecules likely present in early atmosphere can combine to form large organic molecules (nucleic acids, amino acids, proteins, lipids) if electrical energy is present
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CH4 NH3 H2 H2O
electric sparkchamber
condenser
An electric spark simulatesa lightning storm
Organic moleculesappear after a few
days
Energy from the sparkpowers reactions amongmolecules thought to bepresent in Earth’s early
atmosphere
When the hot gases inthe spark chamber are
cooled, water vaporcondenses and anysoluble molecules
present are dissolved
Boiling water addswater vapor to the
artificial atmosphere
boiling chamber
water
cool waterflow
17.1 How Did Life Begin17.1 How Did Life BeginMiller-Urey Experiment
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• Modern geochemists believe early atmosphere was slightly different from that modeled in Miller and Urey’s experiments
• Additional experiments with more realistic (but still oxygen-free) simulated atmospheres have also yielded organic molecules
• Electricity not the only suitable energy source (heat and UV light)
17.1 How Did Life Begin17.1 How Did Life Begin
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17.1 How Did Life Begin17.1 How Did Life Begin
• Prebiotic synthesis neither efficient nor fast
• prebiotic molecules threatened by sun’s UV radiation since Earth lacked an ozone layer
•Ozone layer is a region high in today’s atmosphere made up of ozone molecules (O3 – formed when solar energy splits O2 molecules into individual O atoms which then react with other O2 molecules)
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Ozone Formation
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Ozone layer
• UV radiation can provide energy for formation of organic molecules but can also break them apart
• organic molecules may have accumulated under rock ledges or bottoms of shallow seas away
from UV radiation
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• RNA may have been the first self-reproducing molecule– DNA was probably not the earliest informational
molecule
• DNA requires large
complex protein enzymes
–Instructions for
building these enzymes
are coded in DNA
17.1 How Did Life Begin17.1 How Did Life Begin
http://www.sciencechannel.com/tv-shows/through-the-wormhole/videos/through-the-wormhole-from-rna-to-dna.htm
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17.1 How Did Life Begin17.1 How Did Life Begin
• RNA can act as a catalyst (speeds rxns)– Thomas Cech and Sidney Altman (1980s) discovered a
cellular reaction that was catalyzed by a protein, a small RNA molecule and coined the term ribozyme
– Dozens of natural occurring
ribozymes have been discovered
since; found to catalyze reactions
including attaching amino acids to
growing proteins
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• Ribozyme discovery led to hypothesis that RNA preceded origin of DNA– first ribozyme continued to evolve and gradually
developed into is present role as intermediary between
DNA and protein
synthesis
17.1 How Did Life Begin17.1 How Did Life Begin
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• Self-replicating molecules on their own DON’T constitute life
– membrane-like vesicles may have enclosed ribozymes
– Protocells – spherical collection of proteins & lipids containing ribozymes
(stepping stone to 1st cells)
17.1 How Did Life Begin17.1 How Did Life Begin
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• Earth formed 4.5 b.y.a and was HOT
– Meteorites smashed into forming planet; kinetic energy converted into heat on impact
• Geologic evidence suggests Earth cooled enough for water to exist in liquid form 4.3 b.y.a.
• Oldest fossil organisms found (so far) are approximately 3.4 b.y.o
• Life arose 3.9 b.y.a. in Precambrian era
17.2 What Were the Earliest Organisms Like?17.2 What Were the Earliest Organisms Like?
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1. Relative Dating (before 20th century)
a. Law of Superposition - Fossils in deeper rock layers were older than fossils found in shallower rock layers
2. Absolute Dating (1896)
a. Radiometric dating – when the nuclei of
radioactive elements spontaneously break down,
or decay, into other elements
b. Each radioactive element decays at a different
rates
http://education-portal.com/academy/lesson/the-history-of-life-on-earth-timeline-and-characteristics-of-major-eras.html#lesson (cuts off after a while)
How Do We Know How Old a Fossil Is? 17-1How Do We Know How Old a Fossil Is? 17-1
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How Do We Know How Old a Fossil Is? 17-1How Do We Know How Old a Fossil Is? 17-1
2. Radiometric dating (cont.)
a. Time it takes for half of a radioactive element’s
(isotope) nuclei to decay at a specific rate is called
half-life.
b. Half-life of Carbon-14 = 5,730 years
Half-life of Potassium-40 = 1.25 billion years
c. Can estimate how much time has passed by
measuring the proportion of decayed nuclei to
undecayed nulcei
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Half-livesHalf-lives
256 14C atoms at time 0
128 14C and
128 14N atoms
after 5,730 years or
1 half-life
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Half-livesHalf-lives64 14C and
192 14N atoms
after 11,460 years or
2 half-lives
32 14C and
224 14N atoms
after 17,190 years or
3 half-lives
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Half-livesHalf-lives16 14C and
240 14N atoms
after 22,920 years or
4 half-lives
8 14C and
248 14N atoms
after 28,650 years or
5 half-lives
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Half-livesHalf-lives4 14C and
252 14N atoms
after 34,380 years or
6 half-lives2 14C and
254 14N atoms
after 40,110 years or
7 half-lives
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Pro
port
ion
of is
otop
e le
ft
1/4
1/8
1/16
1
1/2
30 4 52Half-lives
1
Proportion of Isotope Left vs. Half LivesProportion of Isotope Left vs. Half Lives
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3. Hyphen notation of radioisotopes (element symbol and mass number)
Examples: C-12, C-14, O-16, O-18
4. Carbon-14 dating – compare ratio of C-14 and C-12 and use the ratio to determine age
How Do We Know How Old a Fossil Is? 17-1How Do We Know How Old a Fossil Is? 17-1
ISOTOPE
Carbon-14
Uranium-235
Potassium-40
Uranium-238
HALF LIFE (years)
5,730
704,000,000
1,250,000,000
4,500,000,000
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Sample Problem 1:
The half-life of Thorium-230 is 75,000 years.
If a scientist has 40.0g of Thorium, how
much will remain after 225,000 years?------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
How many half-lives have past? How much Thorium is left?
225-75 = 150
150-75 = 75 40/2 = 20g
75-75 = 0 20/2 = 10g
3 half-lives have past 10/2 = 5g 5g of Thorium remaining after
225,000 years
How Do We Know How Old a Fossil Is? 17-1How Do We Know How Old a Fossil Is? 17-1
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2. The half life of carbon-14 is 5,730 years. How long will it take for ½ of the sample to decay?
1 half-life = 5,370years = ½ the sample decays
3. If a biologist has 64.0g of C-14, how long will it take until 8.0g remain un-decayed?
64/2 = 32g 1 half-life 5,730 x 3 half-lives =
32/2 = 16g 1 half-life 17, 190 years
16/2 = 8g 1 half-life
3 half-lives
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The first organisms were anaerobic (don’t require oxygen to metabolize nutrients) prokaryotes (lack membrane bound nucleus)
- Obtained nutrients & energy by absorbing organic molecules from their environment (heterotroph hypothesis)
17.2 What Were the Earliest Organisms Like?17.2 What Were the Earliest Organisms Like?
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17.2 What Were the Earliest Organisms Like?17.2 What Were the Earliest Organisms Like?
• Some organisms evolved ability to capture sun’s energy when organic molecules were used up (photosynthetic bacteria)
– Photosynthetic organisms
release oxygen
– Oxygen reacted with iron
within Earth’s crust to form iron oxide (rust)
which is why rocks formed during that time contain lots of iron
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17.2 What Were the Earliest Organisms Like?17.2 What Were the Earliest Organisms Like?• Excess oxygen began accumulating in
atmosphere (approx. 2.3 b.y.a) probably produced by bacteria like cyanobacteria
– Very likely we are breathing some of the recycled oxygen expelled more than 2 b.y.a!!!!
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• Aerobic metabolism arose in response to dangers posed by oxygen
• Oxygen can react with organic molecules breaking them down
• Oxygen may have exterminated many anaerobic organisms (natural selection)
• Evolution of aerobic metabolism was significant because aerobic organisms can harvest more energy per food molecule than anaerobic organisms
17.2 What Were the Earliest Organisms Like?17.2 What Were the Earliest Organisms Like?
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• Some organisms acquired membrane-enclosed organelles• Ability to compartmentalize functions inside the
cell improved efficiency of early cells• First eukaryotes (membrane- bound organelles) appeared 1.7 b.y.a.
17.2 What Were the Earliest Organisms Like?17.2 What Were the Earliest Organisms Like?
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• Mitochondria and chloroplasts may have arise from engulfed bacteria• Endosymbiosis hypothesis proposes that early
eukaryotic cells acquired precursors of mitochondria and chloroplasts by engulfing certain types of bacteria
17.2 What Were the Earliest Organisms Like?17.2 What Were the Earliest Organisms Like?
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https://www.youtube.com/watch?v=bBjD4A7R2xU
photosyntheticbacterium
Descendants of thephotosynthetic bacteriumevolve into chloroplasts
The mitochondria-containing cell engulfs aphotosynthetic bacterium
Descendants of theengulfed bacteriumevolve into mitochondria
aerobicbacterium
An anaerobic,predatory prokaryotic cell engulfs an aerobicbacterium
Endosymbiosis Hypothesis
•Evidence? Many distinctive biochemical features shared by eukaryotic organisms and living bacteria
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17.2 What Were the Earliest Organisms Like?17.2 What Were the Earliest Organisms Like?
D-Anaerobic, prokaryotic, heterotrophs evolve from protocells (heterotroph hypothesis)
B- Evolution of autrophic pathways chemosynthesis/photosynthesis
H-Anaerobic, prokaryotic, autotrophs evolve (cyanobacteria)E-Oxygen released by photosynthesizers
I- Aerobic prokaryotes evolveC- Endosymbiosis of aerobic prokaryotes (mitochondria) into
anaerobic autotrophic prokaryotesG-Endosymbiosis of autotrophic prokaryotes (chloroplasts) into
aerobic prokaryotesA-Evolution of eukaryotes
F-Evolution of multicellular organisms
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Review the followingReview the following::
Ch. 1: Introduction to Life on Earth1.Read Ch. 1 summary of key concepts on pg. 162.Read the Ch. 1 Learning Outcomes on pg. 173.Complete the Chapter 1 Review
- Pg 17; 1-7 and 1-64. Ch. 1 online resources at http://www.masteringbiology.com4.Chapter 1 Vocab
--------------------Ch. 17-1 and 17-2: History of Life--------------------1. Read Ch. 17-1 and 17-2 summary of key concepts on pg. 3342. Read the Learning Outcomes (LO1 and LO2) on pg. 3353. Complete the Chapter 17 Review
- Pg 335; any question pertaining to LO1 and LO24. Ch.17-1 &17-2 online resources at http://www.masteringbiology.com4.Chapter 17-1 and 17-2 Vocab