Earth History

Eons – largest time division Eons determined by major changes in the Earth Most recent Eon started with the appearance of multicellular animals = Phanerozoic Eon Three Eons make up what was previously know as the Precambrian Period 1) Proterozoic 2) Archean 3) Hadean

The Hadean Eon: 4560 to 3800 million years ago 4.6 to 3.8 billion years ago Earth & other planets formed from dust and gasses surrounding the sun

Heavy elements in the planets suggest the dust/gas came from a supernova We can observe other solar systems forming today They form in diffuse nebulae like nebula M16.

Gravity gathers dust into large lumps, called planetisimals Collisions between lumps makes lots of heat The Earth was molten during the Hadeon Eon. Steam atmosphere formed from light elements

After most planetisimals had become part of a planet, there were fewer collisions Earth’s temperature dropped below 1,000 ۫C First rocks formed as crust cooled The oldest Earth rocks currently known are 3.8 billion years old. The oldest meteorites and lunar rocks are about 4.5 billion years old Erosion and plate tectonics have probably destroyed all of the Earth rocks older than 3.8 billion years.

The Archaean Eon: billion years ago Began with the formation of solid rock Volcanic activity added heavier gasses to atmosphere (CO 2, N 2 ) Water condensed Early oceans formed First life appeared on Earth

Archean Atmosphere likely carbon dioxide, water vapor, nitrogen, carbon monoxide, hydrogen sulfide, hydrogen chloride (CO 2, H 2 O, N 2, CO, H 2 S, HCl) What’s missing? Still present in modern atmosphere Rare in modern atmosphere

WHEN Did Life Evolve? oldest fossils of life-forms ~3.5 byo life likely evolved before then, but no fossils Microscopic sized cells w/o cell walls leave few fossils Life must have evolved before there was free oxygen in the atmosphere O 2 breaks down macromolecules If macromolecules could not form…. …....living cells could not form

Archean sediment dark-colored = unoxidized Archean sediments were deposited before there was free oxygen (O 2 ) in the atmosphere oxidized (rusted) sediment appears about 2.2 billion years ago in the Proterozoic Eon The free oxygen was produced by living cells doing photosynthesis Therefore, life must have evolved before 2.2 bya

Origin of Life 1) monomers form by chemical rxns. 2) monomers join to form macromolecules 3) cell membranes form from lipids 4) proteins begin to break-down organic molecules to release energy 5) DNA or RNA inside cell membrane begin to pass genetic information from mother cells to daughter cells. 6)……LIFE!

Can All of This Happen on its Own?? Can monomers like amino acids form by themselves? Can lipids make themselves into membranes? Experiments have shown that they CAN! Amino Acids

Monomer Synthesis Miller and Urey - created “Early Earth Apparatus” Archaen atmosphere in the top electrodes to produce “lightning” Archean ‘ocean’ in the bottom

Results: after a week, primordial ocean became primordial soup 12 of 20 most common amino acids Further experiments produce nucleic acids and sugars

Macromolecules chains of molecules proteins carbohydrates lipids nucleic acids

Requirements for making Macromolecules energy source: to drive reactions protection: from too much energy concentration: to bring materials together so they can react together

Energy Source Energy induces chemical reactions volcanoes lightening cosmic rays UV radiation

Protection too much energy can be a bad thing! New Moleucles protected by: rock ledges or ice under thin sediment film just under surface of water

Concentration when chemicals are spread out in water, reactions are less likely to happen concentration brings reactants together evaporation freezing scums droplets, bubbles clay

Concentration - clay clay forms from sedimentary particles called platelets platelets are: – very small – flat – with negative charge on surface

Clay organic molecules are attracted to clay surface Organic molecules concentrate and align Examples: bentonite (kitty litter, mud masks), kaolinite (Kaopectate)

Can cell membranes form from Phospholipids? each phospholipid macromolecule has a hydrophobic end and a hydrophilic end when surrounded by water, phospholipids form a sphere hydrophobic ends protected on the inside

Protobionts Naturally formed phospholipid spheres Macromol. & enzymes concentrated inside Protobionts can: maintain their structure increase in size over time divide when too large Metabolize starch selectively absorb and release compounds store and release energy

Are Protobionts Alive? No they can’t replicate themselves

Replication process by which organisms make copies of themselves Replication must include passing on of genetic material (heredity) Simplest replication is by binary fission Replication by binary fission is found in modern day 1) bacteria 2) single cells plants/animals (by mitosis)

Origin of Heredity Many different types of protobionts exist those best able to gather organic molecules, grow, & divide become most common but “competition” is useless unless traits can be passed on/inherited = no evolution = no progress Heredity requires polymers that can replicate themselves: DNA and RNA

Origin of Heredity short strands of RNA can assemble naturally RNA strands can replicate themselves if more monomers available Zinc & Copper act as catalysts RNA most likely the first molecule of to pass on genetic info

WHERE Did Life First Evolve? Desirable features: – energy source – protection – chance for concentration – warm (chemical reactions work faster) – wet (life requires liquid water) – good supply of chemicals/nutrients

Tropical Lagoons Mud flats & Tide Pools

Hot Springs Conditions very like Archean Earth High Temperatures Low free oxygen Archeabacteria live here today

boiling water from vents through crust very stable environment Lots of clay fro concentration very protected lots of minerals warm -> hot Archaebacteria Deep Ocean

Aliens? some meteorites up to 6% organic molecules comets up to 20% organic sludge Halley’s Comet contains: C, O, H, N, CO 2, ice, nucleic acid bases, amino acids and formaldehyde 74 amino acids identified so far from meteorites