ORIGIN OF LIFE ON EARTH

Campbell and Reece, Chapter 26

When I was in 9th grade biology (1961-1962) I read a paper (The origin of life, Scientific American, August 1954) by George Wald (who won a Nobel Prize in 1967), tha reading that paper had a great impact on me.

Panspermia - seeds of life distributed everywhere
Extraterrestrial origin
Spontaneous generation discredited:
(1) Redi (1600's show maggots on meat need flies to lay eggs)
(2) Pasteur microorganisms
TRANSPARENCY (Fig. 26.9)

Universe 15 - 20 billion years old
Earth 4.6 billion
Earth has water as liquid, many heavy elements

TRANSPARENCY (Fig. 26.4) Haldane = Oparin theory, Miller & Urey experiment to reconstruct synthesis of organic molecules using water, methane, hydrogen and ammonia.

Early atmosphere (there's still some debate): Nitrogen (N2), Hydrogen (reducing = build-up), Methane (for C, H), Ammonia (for N, H), Carbon dioxide (for C, O), Water (for H, O), also some Hydrogen - sulfide (S), CO (carbon monoxide)

No (or very little) Oxygen O2 (oxidizing = break-down) or Ozone O3 (block UV)

Now N2 78%, O2 21%, CO2 0.3% + others (Argon)

Primordial hot dilute soup
"chemical" vs. "biological" evolution
amino acids hook together with "geologically relevant" heating like lava
amino acids - proteins, nucleotides - RNA, DNA, ATP
Eventually, DNA became the major hereditary molecule because it is so stable.
TRANSPARENCY (Fig. 26.11) Probably RNA was the first hereditary material.
polysaccharides
Coacervates (microspheres, protobionts) = droplets, aggregates
TRANSPARENCY (Fig. 26.12)In the laboratory, such protobionts have been made.
Prokaryotes then Eukaryotes
Fossil record rich back to 600 million yrs old
TRANSPARENCY (Fig. 25.2) 14C dating in fossils is important
Earth and Mars 4 1/2 billion yrs. old
first 1/2 billion yrs unsuitable for life
3.2-3.5 billion yrs ago first fossils
Precambrian - Salt marsh - blue-green algae, no fish algal mats rock fossils

Ferment (energy and CO2) (anaerobic = w/o oxygen)

Photosynthesis 6 CO2 + 6 H2O -- C6H12O6 (glucose) + O2

Animals - motility, sensory

Respiration (metabolism, aerobic)

Ozone from O2 (before all life in sea)
(depletion with freon = fluorocarbons)

Invasion of land - vascular, support, mating without water

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