Transcript Origins of Life: Formation of The Earth

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
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 a
microsphere that is selectively permeable
 The spheres 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
 4 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  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
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)
 “Great Dying”-90% of all known species lost; volcanic
eruption, increase in gases, temperature
 Pangea breaks apart, forming Gondwana and Laurasia
Paleozoic Era (570-240 mya)
 Carboniferous period
 forests began to
turn to coal, source of
biofuels we use today
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 land mass collisions
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forming 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