Primordial EarthPrimordial Earth

Theories on the Origin of LifeTheories on the Origin of Life

Early Earth and EvolutionEarly Earth and EvolutionA THEORY of the origins of the universe A THEORY of the origins of the universe

Big BangWhen?

-Approx. 13.5 Billion years ago expansion from singularity-MASSIVE AMOUNTS OF ENERGY!-Energy eventually converted to fundamental building blocks of matter.

Evidence?-Expanding universe-Background radiation-Abundance of Hydrogen

After Big Bang…….After Big Bang…….• Stars!

– Need hydrogen gas fusion– Form heavier elements– Really big stars go out with a bang supernova!

• Planets!– Leftover “mess” from supernova start to accrete

into larger objects. (NEWTONS LAW!)– Typically these objects will orbit around a star

• SOLAR SYSTEMS!

LIFE!!!!LIFE!!!!

• Spontaneous Generation.– Theory (hypothesis actually) that life can

randomly emerge from non-living thing

• Biogenesis – Theory that life only comes from pre-existing life.

• Common Ancestor– Theory that every living organism on the planet

is a descendent of an original cell

• Question : Where did first life come from???

Oparin-Haldane HypothesisOparin-Haldane Hypothesis

• All the elements were already present on Earth.

• Early atmosphere contained mostly ammonia NH3, hydrogen gas H2, water H2O, and methane CH4.

• High temperatures might cause gases to form simple organic compounds.

““Prebiotic Soup”Prebiotic Soup”

• As Earth cooled simple organic compounds collected in the lakes and seas.

• Energy from lightning and UV radiation caused chemical reactions to build macromolecules.

Key ExperimentsKey Experiments• Francisco Redi’s Flies –

–Where do maggots come from

–Bottom Line: no spontaneous generation

Key ExperimentsKey Experiments• Spallanzani –

–Bacteria in broth come from air? Or other microbes?

–Bottom Line: no spontaneous generation

Key ExperimentsKey Experiments• Louis Pasteur –

–Bacteria in broth come from air? Or other microbes?

–Key difference from spallanzani?–Bottom Line: no spontaneous generation

1953: Miller- Urey1953: Miller- Urey

• Stanley Miller and Harold Urey set up an apparatus to simulate the proposed primordial Earth conditions.

1953: Miller- Urey1953: Miller- Urey

• Stanley Miller and Harold Urey set up an apparatus to simulate the proposed primordial Earth conditions.

• Found organic compounds.

Debatable points:Debatable points:• Atmosphere probably contained CO,

CO2, and N2

• Presence of O2, and CO2 interfere with production of organic compounds.–Organic compounds produced in

undersea volcanoes.• Organic compounds came from outer

space.

Pre-Cell StructuresPre-Cell Structures

• Organic molecules aggregate spontaneously.

• Microsphere: Protein membrane structure

• Coacervates: Droplets of lipids amino acids, and sugars.

Microspheres

Coacervates

First Cells: ProkaryoticFirst Cells: Prokaryotic• Environment: Little or no oxygen

Cells were anaerobic.• Environment: Organic food

molecules

Cells were heterotrophs.• Oldest fossils look like prokaryotes.

Cells were prokaryotes.

ArchaeaArchaea

• Present day cells, thought to be similar to earliest cells.

• Unicellular organisms that thrive in harsh environmental conditions.–Anaerobic metabolism.–Inorganic energy sources.

Endosymbiotic TheoryEndosymbiotic Theory

Creating the first eukaryotes:

• Large prokaryotes engulfed smaller prokaryotes.

• Mutually beneficial relationship: small cells are protected and large cell gets energy.

• Small aerobic cells evolved into

• Small photosynthetic cells evolve into

• Mitochondria and chloroplast have their own DNA.

• DNA is circular, like prokaryotes.

• Replicate independently of cell.• http://www.youtube.com/watch?v=dSjg_uYS_QY&feature=related

chloroplast.

mitochondria

SummarySummary1. Small organic molecules were

synthesized.

2. Small organic molecules (monomers) joined to form polymers, like protein and nucleic acids.

3. Molecules could self-replicate.

4. Molecules were packaged into membrane structures- resembling the first prokaryotic cell.