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