06/09/12
Origin and evolution of life
1. Origin of life
- life arose once diversify to present
Evolution: genetic alteration and resulting phenotypic change in populations of
organisms occuring across generations
Evolutionary relationships can be tracked through:
- fossil record (changes over time)
- when organisms evolved/environment in which they lived
- morphological comparisons (compare over time and btw organisms)
- evolutionary artifacts (eg human pharynx) enable understanding of
relationships between now and before
- development
- embryotic development patterns allow for comparison
- molectular analysis (DNA)
-Similarities in genome and genetic artifacts
-eg Neanderthal DNA is in human genome = interbreeding
- behavior
Origin theories:
Extraterrestrial source: compounds common inside meteors form building blocks of
life
Chemical evolution:
Miller/Urey (1950) experiment: mimic early atmosphere (CH , N , N4 , 2 , H3O, 2 2
CO 2
- Struck with fake lightning
- Result condensed for analysis
- Found monomers: 4 bases in DNA/RNA
- 17-20 amino acids
- 3- and 6-carbon sugars
- In replicated experiments, sulfur compounds found
- Life necessities:
- monomers join by condensation synthesis reactions requiring energy:
- eg. clay, shores, hydrothermal vents, hot pools polymers
- RNA: pre-DNA
- simpler, catalytic (facilitates replication of through ribosomal action)
- lipids naturally form bilayered spheres
- RNA trapped for more stable environment
- Self-replicating structure nucleic acid inside
2. History of life
If earth’s timeline were a 30 day calendar:
- life arose on the 4 day 06/09/12
- recorded humans arose during the last 5 minutes of 30 dayth
Timeline:
4.5 bya: earth forms
3.8 bya: origin of life
2.5 bya: photosynthesis
1.5 bya: eukaryotic life
700 mya: multicellular life
542 mya: Cambrian explosion
420 mya: life on land
200000 ya: humans
Physical changes:
- Continental drift
- Oceanic changes, sea level changes
- Volcanic activity, meteorite collisions
- Change in temp
- Increase in O2
- no O2 to start, bacterial mutations to photosynthesize Energy
from light splits 2 O, reduces CO 2ith O a2 waste
- allow evolution of aerobic respiration
- cyanobacteria, photosynthetic prokaryotes form stromatotlites
Precambrian (largely unicellular): 4.5bya
-life confined to oceans
-unicell
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