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 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.php?storyId=19308778
Origin of Life: Synthesis of Organic Compounds: Miller Experiments
• 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)
Products of Miller experiment reactions: Formaldehyde, Cyanide gas
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 MembranesLipid bilayer (Fluid Mosaic Model) composed of
phospholipids: hydrophilic head + 2 hydrophobic tailsProtects, selectively permeableWhen amino acids are heated and cooled, they form a
microsphere that is selectively permeableThe 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: FossilsBuried 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) dating-measures 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
• 14C has a half life of 5700 years. If your fossil is 60000 years old, how many half lives occurred?
Radiometric Dating Problems4 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 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 formedOrganisms of major lineages formed in oceans (Cambrian
explosion)Major ice age-70% of all marine organisms became
extinctInvasion 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 apartGymnosperms, 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 forming Cascades, Andes, Himalayas, Alps
Warmer and wetter climatesEmergence of mammals as
the dominant land animalsWooly 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/continentsPlate 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