Origin of Life

• Universe formed 15 billion years ago (Big

Bang)

• Galaxies formed from stars, dust and gas

• Earth formed 4.6 billion years ago

Earth 3.5 bya

• Suns energy stripped away 1st atmosphere

• 2nd atmosphere formed from volcanic outgassing

• Primitive atmosphere: CO2, water vapor, lesser

amts of CO, N2, H2, HCl, and traces of NH3 and

CH4 (3.5 bya)

• O2 came in 3.2-2 bya

• Autotrophic Organisms: photosynthesis

• Another environmental change

• Result in evolution

The sum total of the chemical processes that occur in living organisms, resulting in growth, production of energy, elimination of waste material, etc.

• Anabolism- build up of complex molecules

• Catabolism- break down of complex molecules

Metabolism

• Autotrophs– Organisms that get their energy by

making their own food (like plants)– Plants capture energy from the sun, use

water and carbon dioxide to make sugars and starches

• Heterotrophs– Organisms that take in food to meet their

energy needs– Animals must consume autotrophs

(plants), and other heterotrophs to meet their energy needs

Earth’s Atmosphere

OxygenEvidence for O2 production:

Banded Iron Formations (BIF) BIF found in ocean sediments red

bands are high in Fe2O3 and Fe3O4 (red bands)- forms when reduced iron reacts with O2

Photosynthesis

6H2O + 6CO2 + light C6H12O6 + 6O2

“Oxygen revolution”

Time (billions of years ago)

4 3 2 1 0

1,000

100

10

1

0.1

0.01

0.0001

Atm

osp

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ric

O2

(pe

rce

nt

of

pre

sen

t-d

ay

leve

ls;

log

sc

ale

)

0.001

Oxygen

Evolution of Ozone• Accumulation of free O2 in the atm also led to

the accumulation of ozone– Ozone important for blocking incoming UV

radiation

• Even small amounts of atm O2 leads to enough ozone to provide some protection against UV– Partial screen likely to have formed ~ 1.9 bybp– Presence of this UV filter allowed life to move out

of the oceans and onto land– Consistent with the timing of evolution of

eukaryotes and higher plants

• 0.5 billion years ago

• Atmosphere O2 to 1% current

• Compare to present: 78% N2, 21% O2, 0.04% CO2, + trace gasses

• Relatively small, most single cell

• Start of multicellularity

• Increase in cell complexity

Formation of Earth’s Oceans(4 bybp):

Rain

Condensation

Off gassing of water vapor from volcano

Life began~ 3.5 bya

Organic molecules (C H O N P S) swimming in shallow seas

Stage 1: Abiotic synthesis of organic molecules such as proteins, amino acids and nucleotides

Stage 2: joining of small molecules (monomers) into large molecules

Stage 3: origin of self-replicating molecules that eventually made inheritance possible

Stage 4: packaging these molecules into pre-cells, droplets of molecules with membranes that maintained an internal chemistry

Thomas Huxley- Search for origin of life

Wyville Thompson: HMS Challenger (1872-1876) found it was actually diatomacous ooze reacting with seawater and ethyl alcohol

Bathybias heckali- primordial ooze

Miller and Urey’s Experiment

ELECTRICITY!!!

Organic molecules like amino acids

Produced:• 20 amino acids• Several sugars• Lipids• Purine and pyrimidine bases (found in

DNA, RNA & ATP)

END.

RNA worldRNA world

• The first genetic material was probably self-replicating, catalytic RNA not DNA;

• In “RNA world”, RNA could have provided the template on which DNA was assembled

• Once DNA appeared “RNA world” gave way to “DNA world”

• The first organisms were not photosynthetic; they were probably heterotrophic

The RNA world theory says that RNA both stored and catalysed reactions that reproduced genetic information in early evolution.

Protobionts, collections of abiotically produced molecules surrounded by a membrane-like structures

Liposomes can form when lipids or other organic molecules are added to water.

- Have a bilayer- Can undergo osmosis- Can “reproduce”

Protocell (Protobiont)Fatty acid membrane with ribozymes inside

OxygenEarliest Evidences: oldest fossilsOldest photosynthetic microbes 3.5-3.2 B.Y.

- Bacterium-like- Unicellular- Evidence for breakdown products of photosynthesis

Cyanobacteria, 3.5 B.Y.

Stomatolites, 3.5- 0.7 B.Y.

Three-domain systemExtremophilesProkaryotes Eukaryotes

Look at how this evolution happened!

chemosynthetic bacteria (extremophiles)

Chemosynthesis:

02 + 4H2S + C02 CH20 + 4S +3H20

Stromatolites (bacteria & cyanobacteria)

Oldest fossils found in western Australia and southern Africa ~ 3.5 byo

Photosynthesis:

6H2O + 6CO2 + nutrients + light energy C6H12O6 + 6O2

Cellular Respiration

C6H12O6 + 6O2 6H2O + 6CO2 + energy

Stromatolites from Shark’s Bay Australia

mostly cyano

Early prokaryotes may have arisen near hydrothermal vents

Hydrothermal vents are rich in sulphur and iron-containing compounds needed for ATP synthesis. Temperatures can reach 120 C.

Hot springs in Yellowstone National Park – pigmented bacterial mats