Transcript HISTORY OF LIFE

Bio 4/17
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HISTORY OF LIFE
Chapter 14
The Record of Life
Ch. 14, Sec 1
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
Formation of Earth, ~4.6bya
• Date determined by
studying the layers of rock
that make up the planet
• Conditions of early Earth
– Hot due to no atmosphere to
block UV rays from the sun
• No oxygen to breath
• A lot of carbon dioxide and
water
Life’s Origins, ~3.9 to 3.4 bya
• Life originated in
Earth’s oceans
• Early life forms were
similar to bacteria
– Single cells
– No membrane-bound
nucleus
History of Life in Rocks
• Rocks provide information about Earth’s history
including the history of life on Earth
• Paleontologists study ancient life and fossils
• 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
Dating Fossils
• Relative Dating = layers of rocks have
different ages, the “youngest” layers on
top; older fossils found in older layers of
rock
• Radiometric/radioactive 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
Geologic Timescale
• Begins (on the
bottom) with the
formation of Earth
and continues up
through present time
• Scale is divided by
the kinds of
organisms that lived
during that time
• Layers of rock match up with the
Geological Timescale
Organization of the GTS
• 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
4 Eras
1. Precambrian Era
• Beginning of the geologic time scale
(GTS), longest era, 87% of Earth’s history
• Oldest rocks are from the Precambrian,
oldest fossils too
• First organisms were single celled
2. Paleozoic Era
• Cambrian Explosion
occurred during the
Cambrian Period.
• Enormous increased
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
3. Mesozoic Era
• began 248 million
years ago
• Dinosaurs died out
during another mass
extinction making
room for mammals
• Meteor crash could
have caused the
mass extinction
4. Cenozoic Era
• Began 65 million
years ago
• Increased diversity in
mammalian life
• Modern humans
appeared 200,000
years ago
• As you move towards the bottom of the
rock layers, you move back on the
Geological Timescale
• Similar fossils may be found on different
continents because at several times in
Earth’s history the continents were
connected in different patterns
• 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.berk
eley.edu/geology/teca
ll1_4.mov
The Origin of Life
Ch. 14, Sec. 2
Spontaneous Generation
• Pre-17th century it was believed that living
things arose from nonliving things through
a process called Spontaneous
Generation
• 6th century BC: Greek
philosophers propose
life arose when
sunlight was shined
onto mud
• Why?
• 1600’s: It was believed that mice appeared from
rotten grain
• Why?
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
• 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…
• 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
• ..\..\..\HowStuffWorks Videos One Step
Beyond Maggot Therapy.flv
Louis Pasteur (1822-1895)
• Finally disproved
spontaneous generation
once and for all! 200
years after Redi’s
experiment
• Pasteur set up an
experiment where boiled
broth was exposed to air,
but microorganisms
couldn’t fall in
• By the 1800’s scientists understood
(thanks to the microscope invented a
century ago) that microorganisms
(bacteria & viruses) caused people to get
sick
• But….
• Some scientists still believed that bacteria
and viruses spontaneously generated from
the air
• Pasteur proved them wrong with his
experiment
• 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!!!
• Thanks to Pasteur….
• Biogenesis = living
organisms come from other
living organisms
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)
• 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
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)
Alternative Hypotheses
• 1. Life (biomolecules)
emerged in ice
(Stanley Miller)
• Within ice there are
chemicals to create
biomolecules &
microscopic pockets
of water
• 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
• 2. Life (biomolecules)
emerged in deep sea
vents
• Vents provide the
heat & chemicals that
could cause chemical
reactions to generate
biomolecules
Formation of Protocells
• Protocell = Heating the amino acids can
cause them to take on some life activities
like growth and division
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
• Therefore….
• The first cells were anaerobic,
heterotrophic prokaryotes
• Anaerobic = respiration that doesn’t
require oxygen
• Heterotrophic = needs to eat other things
in order to get the organic molecules
needed for life
• 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
• 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)
Endosymbiotic Theory
• Eukaryotic cells evolved from Prokaryotic
cells
• Symbiosis = close, long term relationship
between species
• An ancient prokaryote engulfed another
prokaryote and instead of digesting it they
lived together
• This explains why mitochondria has its
own DNA
• http://highered.mcgrawhill.com/sites/9834092339/student_view0/
chapter4/animation_-_endosymbiosis.html