LECTURE 3: ORIGINS OF LIFE

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Origins of Earth Review 1. Universe is 13.7 Billion Years Old 2. Solar System formed 4.6 Billion years ago –Most likely Scenerio for formation: –Most matter in universe is light elements (Hydrogen) –Heavy Elements (Carbon, Nitrogen, Oxygen) are formed only in core of dying stars –Nearby Star Exploded –Shockwave through Gas/Dust Cloud caused lumps to form –Lumps Gravitationally move matter to themselves and cloud collapsed upon itself –99.9% of matter formed into the sun, the rest formed bodies such as planets, comets, etc.

Origin of Earth Review The early Earth was a very different place: - atmosphere :mostly carbon dioxide, nitrogen, and water vapor Volcanic Eruptions formed first continents 4.1 BYA Oceans formed when Earth Cooled 4.1 BYA Late Bombardment till about 3.8 BYA

What is the Oldest Fossil of Life on Earth? First Life Fossils: Cyanobacteria ~3.5 bya –Filamentous Strings of up to 40 cells Prokaryotes: –Single-celled organisms –These prokaryotes began to photosynthesize Produced oxygen

Oldest fossils = stromatolites (made by bacteria)

How did the 1 st life form come to exist? Spontaneous generation theory accepted until 1862 Biogenesis (“life creation”) was a mystery… –If life comes from life how did the first life form evolve?

What is SPONTANEOUS GENERATION? Living things could arise from nonliving things Example: Francesco Redi’s Experiment  fly maggots  life arises from life NOT air

SPONTANEOUS GENERATION (continued) Example: Lazzaro Spallanzani’s experiment  microorganisms arise from others not AIR Uncontaminated

SPONTANEOUS GENERATION (continued) Example: Louis Pasteur’s experiment  microorganisms arise from others not AIR

Even though life does not spontaneously generate today  it must have done so at the beginning. What was the primitive (early) environment of Earth like? HOT!!! No oxygen gas (0 2 ) was present Early gases = mostly volcanic gases CO 2, CO, SO 2, H 2 S  MOST LIKELY GASES IN AIR

How did 1 st Life Form? Conditions on early Earth made the Origin of Life Possible In a sequence of stages about 3.8 BYA: 1. Abiotic synthesis of small organic molecules (inorganic  organic) 2. Joining of these small molecules into polymers (monomers  polymers) 3. Packaging of molecules into “protobionts” (“precells/protocells”) 4. Origin of self-replicating molecules

How did Abiotic Synthesis occur? 2 Hypothesis: 1.Oparin/Haldane Hypothesis - Primordial Soup 2. Extra-Terrestrial Source of Complex Organic Molecules

Step One: Chemical Evolution 1920’s Oparin and Haldane (primordial soup) –atmosphere = HIGH energy levels contributed to SPONTANEOUS chemical evolution –Suggested early atmosphere= NH 3, H 2, CH 3, some H 2 0 –Energy was supplied by sunlight and lightning 1 st organic (“life”) compounds may have been synthesized near submerged volcanoes and deep-sea vents Some organic compounds may have come from space –Carbon compounds have been found in some meteorites that landed on Earth (90 amino acids) Once organic monomers were formed the next stage was….

How did Step 2: Polymer Formation occur? Small organic (carbon) molecules polymerize when they are concentrated on hot sand, clay, or rock These molecule form polymers (or chains) of huge life molecules (biomolecules) Miller-Urey Experiment

What was the Miller-Urey Experiment? Stanley Miller: Graduate student working with Harold Urey Build Apparatus to Test Abiotic Synthesis Simulated Early conditions on Earth Electrical Energy provided by spark discharge

Miller-Urey Experiment AMINO ACIDS made!

What was the Miller-Urey Experiment? They found Amino Acids, Nucleic Acids, Fatty Acids, and other Organic Molecules! Repeated many times under many conditions (UV light- simulating the sun) Demonstrated that Oparin/Haldane Hypothesis Reasonable Nobel Prize for Miller and Urey

Did Extra-Terrestrial Sources Bring Complex Organic Molecules to Earth? Miller/Urey Experiment will not work work if Oxygen is present Comets and Meteors probably were an important second source of organic compounds Comets and Meteorites are rich in organic compounds formed abiotically in deep space (water, ammonia, 74 amino acids) Recent experiments show that these molecules would survive impact!

Step 3: Packaging of molecules into “ (“precells/protocells”) How did this Occur? 1.Organic Molecules Accumulate 2. Polypeptides Form 3. Some assemblages were capable of carrying out primitive living reactions 4. Conversion of pre-cellular assemblages into organized cells enclosed by outer boundary membranes

What are the Hypothesis for Protocell Formation? 2 Hypothesis (maybe Both!!) –Lipid Membrane Hypothesis Liposomes - Lipids(fatty acids) that form vesicles –Formed in Hydrothermal Vents –Research has shown that some minerals can catalyze hydrocarbon tails of fatty acids from H and CO gases –Coacervates - combo’s of proteins, lipid membrane and carbs –Fatty Acid Formation AnimationFatty Acid Formation Animation –Iron-Sulfide “Chimney” Hypothesis When hot iron sulfide in deep ocean vents, meets the cooler ocean, some of the mineral forms into chimneys These chimneys acted as membranes

What were the First “Cells”? Protocells – ABIOTIC molecules surrounded by membrane - like structures Some properties associated with life Simple reproduction and metabolism Maintenance of internal environment –Has membrane All were spontaneously FORMED by chance!

STEP 4: Which Came First RNA or DNA? RNA! Trapped inside a “precell” by chance about 4.0 BYA RNA came 1 st b/c has the following properties: –SIMPLE!!! Less complex/less stable than DNA –RNA  protein more direct than DNA  Protein –Has 3 different phenotypes (characteristics), can fold into diverse shapes –RNA can self assemble from individual nucleotides (polymerize easy  1 strand) –RIBOZYMES: enzymes that can carry out reactions –SHORT STRANDS OF RNA CAN REPLICATE

Which came first autotrophs or heterotrophs? 1.Prokaryotic chemoautotrophs!!!!! 1.Prokaryotic chemoautotrophs!!!!! use chemicals to make their OWN food/energy Prokaryotic photoautotrophs) evolve  pump O 2 in air 2.Cyanobacteria (Prokaryotic photoautotrophs) evolve  pump O 2 in air (around 3.5 bya) 3.Oxygen (O 2 ) in atmosphere results in EARLY mass extinctions b/c it KILLS most life AEROBES 4.Prokaryotic AEROBES (“O 2 loving”) survive 5. Cellular Respiration evolves 6. Single Celled Eukaryotic organisms (around 2.1 bya) Made by Endosymbiosis 7. Multicellular eukaroytic organisms

Photosynthesis and the Oxygen Revolution Oxygenic photosynthesis probably evolved about 3.5 billion years ago in cyanobacteria –A.k.a- Blue/green algae in oceans –They made stromatolites (fossils)

Oldest fossils = stromatolites (made by bacteria)

What were the Effects of O 2 accumulation in atmosphere about 2.7 billion years ago? –Formed Ozone Layer (reduced UV, warmed Earth) ~2.5 bya –O 2  O 3 by UV radiation = ozone Protected from UV rays and provides warmth –Provided opportunity to gain energy from light –Allowed organisms to exploit new ecosystems

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What Were the First Eukaryotes? The oldest fossils of eukaryotic cells date back 2.1 billion years Single celled eukaryotics The theory of endosymbiosis proposes that MITOCHONDRIA and CHLOROPLASTS were formerly small, free-living prokaryotes that were ENGULFED by larger host cells

What is the Evidence Supporting endosymbiosis? Similarities in inner membrane structures and functions 1.Both have their own circular DNA 2.Both have their own ribosomes

First Eukaryote Fossil

What was the First Multicellular Eukaryote? Single cell  Multicellular eukaryotes appeared ~1.5 bya Oldest known fossils of eukaryotes  relatively small algae (~1.2 bya) –Coiled, ribbon-like, 2mm wide 5-15 cm long

What were the Earliest Multicellular Eukaryotes Animals (METAZOA)? –600 MYA (after 85% of history of life!!!) –Sponges then Jellyfish then Flatworms Marine, Soft-Bodied (No mouth, guts, head etc) Absorbed nutrients through Diffusion Why can we find fossils, if they are soft-bodied?

What is the Ancestor to Metazoa? Choanoflagellates – based on DNA and Morphology –Protists that form spherical colonies

Worm Jellyfish

14 billion- BIG BANG  Solar system begins to form 4.6 billion –Earth and other planets (Solar system) is formed 4.2 billion- Earth’s atmosphere, oceans and crust form 3.9 billion- Oldest rocks found (Canada) 3.9 billion- 1 st life on Earth (chemoautotrophs) 3.5 billion- Cyanobacteria on Earth  O 2 Revolution (photoautotrophs) 3.0 billion- 1 st fossils: algae, fungi, bacteria abundant (inverts) 2.0 billion- 1 st Eukaryotic life (small) 700 million- Rodinia causes SNOWBALL EARTH 600 million- Once climate warms  Jellyfish, sponges, and worms abundant (SIMPLE aquatic life) 570 million- Arthropods appear 543 million- 1 st ICE AGE ALL 3 DOMAINS (Archaea, Eubacteria, Eukarya) REVIEW MAJOR EVENTS TO KNOW PRECAMBRIAN ( mya)