CH 25 ~ HISTORY OF LIFE ON EARTH

The Origin of Life

1st fossil evidence 3.5 BYA (Earth ~4.6 BY old)

4 stages 1 – abiotic synthesis of

organic molecules 2 – formation of

macromolecules 3 – formation of

protobionts 4 – formation of self-

replicating molecules

Experimental evidence for the origin of life: Stanley Miller

Heated water (H2O), methane (CH4), ammonia (NH3), hydrogen (H2), and electrical charge

Amino acids were produced

Others determined RNA may have been the first macromolecule with enzyme activity

Follow-up:

Which gas was least abundant in Earth’s early atmosphere, prior to 2 BYA? Oxygen Carbon dioxide Methane Water vapor Ammonia

Protobionts

Molecules derived abiotically that are surrounded by a crude membrane

2 key traits: Accurate

reproduction Metabolism

Origin of Unicellular Prokaryotes: 3.5-3.9 BYA (3:00)

Stromatolite: layered rocks formed by prokaryotes that bind sediment films together

Origin of Eukaryotes: 2.1 BYA (7:00)

Origin of Multicellularity: 1.2 BYA (8:00)

Confined to only a few areas due to several Ice Ages

Probably originated through cooperation of cells that each adopted specialized tasks

Follow-up:

If natural selection in some environment favored the production of daughter cells that were genetically different from mother cells, one should expect selection for:

I – polynucleotide polymerases with low mismatch error rates

II – polynucleotide polymerases without proofreading capability

III - polynucleotide polymerases with proofreading capability

IV - polynucleotide polymerases with high mismatch error rates

Cambrian Explosion: 535 MYA (10:00)

Extensive diversification of animal kingdom

Occurrence of predation features Claws, claspers defense – spines,

body armor

Colonization of land: 500 MYA (10:20)

Fungi, plants, & animals move onto land

Associated with critical adaptations to terrestrial life

Appearance of Homo sapiens: 195,000 YA (11:59 and 59 sec)

Factors affecting evolution of species, I

Continental drift

Important in biogeography and climate changes

Mass extinctions: Permean, 251

MYA Cretaceous, 65

MYA

Factors affecting evolution of species, II

Adaptive Radiation

Periods of evolutionary change in which species are adapting to new ecological roles

Factors affecting evolution of species, III

Slight genetic differences can produce major morphological differences in species

HOMEOTIC GENES

Evolution is NOT goal-oriented

It all comes down to two things: survival and

reproduction

Exaptation: use of existing structures for new purposes

Paedomorphosis: using juvenile structures in adult organisms