Transcript Origins of Life: Formation of The Earth

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Origins of Life: Formation of The Earth
• The earth is 4.6 bya. How did it
form?
• As large clouds of gases cooled,
gravity pulled minerals,
asteroids, rocks together forming
the earth
Earth is composed of:
• Crust-outer layer made of
basalt, granite
• Mantle-intermediate density
layer of rock
• Core-inner layer of molten
nickel, iron
http://www.youtube.com/watch?v=QDqskltCixA
Earth’s First Atmosphere
 A mixture of gases: H2, N2, CO, CO2
 No O2 present
 H2O present after the crust cooled, and rains began,
first seas formed
 Without the presence of H2O, cell membranes would
not have formed; no membranes, no cells
Lipids are known to spontaneously form
bilayered vesicles in water
Origin of Life: Synthesis of Organic
Compounds (monomers)
• All living cells are made of
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carbohydrates, proteins,
nucleic acids, lipids
How did they form initially?
Stanley Miller Experiments
Combined CH4, NH3, H2O, H2
in glass apparatus under a
vacuum and an electrical spark
Amino acids spontaneously
formed in less than a week
(amino acids  proteins)
http://www.npr.org/templates/story/story.ph
p?storyId=19308778
Origin of Life: Synthesis of Organic
Compounds: Miller Experiments
Products of Miller experiment reactions:
Formaldehyde, Cyanide gas
• Formaldehyde  glucose,
ribose, deoxyribose (DNA,
RNA)
• Formaldehyde  porphyrin
ring  chlorophyll A
(photosynthesis)
• Cyanide gas  adenine base
(DNA, ATP, NADPH, NADH)
• Lasting bonds could form
near hydrothermal vents on
sea floor (peptides) in clay
templates (polypeptides)
Which came first, Proteins or RNA?
 Protein first hypothesis: amino acid polymerize
abiotically; enzymatic properties selected; DNA
followed enzyme formation- enzymes needed for
DNA replication and RNA/nucleotide formation
 RNA first hypothesis: RNA can function like
enzymes  self replicating system; RNA genes would
have directed and enzymatically carried out protein
synthesis
Origins of Plasma Membranes
 Lipid bilayer (Fluid Mosaic Model) composed of phospholipids:
hydrophilic head + 2 hydrophobic tails
 Protects, selectively permeable
 When amino acids are heated and cooled, they form
microspheres that are selectively permeable
 The microspheres can incorporate free lipids and in presence of
H2O form bilayer
Origins of Organelles
• Specialized structures with specific intracellular functions:
mitochondria, chloroplasts, RER, SER, golgi, etc.
• Folding of PM inwards may have given rise to the nucleus
and ER
• Endosymbiosis-one bacterium engulfed another and it
survives, both benefiting from the relationship
– Mitochondria/chloroplasts have own DNA
– Mitochondria/chloroplasts resemble certain bacteria in size/structure
– Mitochondria/chloroplasts divide by binary fission
– Outer membrane and inner membrane of Mitochondria/chloroplasts
are different, inner resembles bacteria, outer resembles eukaryotic cell
Origins of Self Replicating Systems and
First Cell
• Abiotic synthesis of small
organic molecules
(monomers)
• Monomers join to form
polymers (clay/vents)
• Aggregation of polymers
inside a plasma membrane
with enzymatic
properties= protocell
• Stability of DNA and
selection for genetic code
creates a self-replicating
system of life
History of Life: Fossils
 Buried remains and mineralized
impression of organisms from the
past; older fossils  deeper
sediment layers (stratum) due to
sedimentation: weathering and
erosion of rocks produce
accumulation of particles
Fossils
• Fossil age is determined
through Radiometric
(absolute) datingmeasures the amount of
isotope in new rock
compared with the
isotope remaining in old
rock; unstable
radioisotopes will decay
to a more stable form
with time
• Index fossils: relative
dating methods used to
identify deposits made at
the same time in different
parts of the world
Fossils
• half life-amount of time it takes for half the
isotope to convert to a more stable form; every
isotope has its known half life
• Radioisotope decay is constant; it does not
depend on pressure, temperature
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14C
has a half life of 5700 years. If your fossil is
60000 years old, how many half lives occurred?
Radiometric Dating Problems
 10.5 half lives occurred. 60000/5700=10.5
 13N has a half life of 25000. How old is your fossil if 4
half lives have occurred?
 If you have only 1/8 of your radioisotope left, how
many half lives have occurred? (1/2n), n = half life
Tree of
Life
• 3.5 bya anaerobic prokaryotic
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cell  Archaebacteria and
bacteria lineages
3.4 bya divergence between
Archae- bacteria and
eukarya
3.2 bya photosynthesis (O2
increases)
2.5 bya cellular respiration
2.1 bya eukaryotic cell
Early eukaryotes
(multicellularity) Fungi,
Plantae, Animalia
How old is the Earth?
Using Uranium 238, earth is
4.6 billion years old
Precambrian Time
• Stromatolites-rocks dating
almost 3.5 bya (contained
prokaryotic cell similar to
cyanobacteria)
• Living stromatolites have
surface covered with
cyanobacteria
Snowball earth: http://www.youtube.com/watch?v=mX3pHD7NH58
The last hypothesized Snowball Earth episode ended just a few million years
before the Cambrian explosion, an extraordinary diversification of live that took
place from 575 to 525 million years ago (discussed in section 8, "Multi-Celled
Organisms and the Cambrian Explosion"). It is possible, although not proven, that
the intense selective pressures of snowball glaciations may have fostered life forms
that were highly adaptable and ready to expand quickly once conditions on Earth's
surface moderated.
Paleozoic Era (570- 240 mya)
 Pangea formed
 Organisms of major lineages formed in oceans (Cambrian explosion)
 Major ice age-70% of all marine organisms became extinct
 Invasion of Land; emergence of vascular plants, fungi, invertebrates,
insects, fish, amphibians, reptiles
Paleozoic Era (570-240 mya)
 Carboniferous period
 forests began to
turn to coal, source of
biofuels we use today
Paleozoic Era (570-240 mya)
 “Great Dying”-90% of all known species lost; volcanic
eruption, increase in gases, temperature, CO2 cycling
 Pangea breaks apart, forming Gondwana and Laurasia
Mesozoic Era (240-65 mya)
 Pangea broken apart, Gondwana and Laurasia begin to
break apart
 Gymnosperms, angiosperms, insects, reptiles dominant
land organisms
Mesozoic Era (240-65 mya)
• First dinosaurs (Triassic
Period), continued
dominance for 140 my
• 65 mya dinosaurs became
extinct; Asteroid impact
causing increase in
temperature and CO2 gas
Cenozoic Era
(65 mya-present)
 Pangea completely broken apart
 Major plate collisions forming
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Cascades, Andes, Himalayas,
Alps
Warmer and wetter climates
Emergence of mammals as the
dominant land animals
Wooly mammoths, saber tooth
tigers, horses, bear-dogs 40-5
mya
Emergence of human ancestors,
humans
Evolution was Influenced by Movement of
the Land Masses
 Continental Drift-movement of land masses/continents
 Plate tectonics-earth has slab like plates that are in constant
movement. This movement is directed by the earth’s molten
core.
 Many mountain ranges formed by the crashing and pushing up
of these plates
Mass Extinctions
 5 major extinctions have occurred through history due to
continental drift, changing temperatures, natural disasters