Download The early earth and the origin of life

Lecture 3:
The early earth and the origin of life
1. What was the early earth like?
2. Could it sustain life?
3. When could life have evolved?
4. Indirect evidence for life
5. The oldest fossils
6. Biotic effects on surface processes
Lecture 3:
The early earth and the origin of life
1. What was the early earth like?
Evidence for the early environment
ripples
pillow
lava
Banded Iron
Formation
pyrite
conglomerate
detrital
pyrite
Lecture 3:
The early earth and the origin of life
2. Could it sustain life?
The chemistry of early life
The locus for the origin of life is unknown.
However, biochemistry closely mirrors
the solubility of elements in seawater
Common to both are:
Na, K, Mg, Ca
S, C, N, P
The metabolism of early life
HETEROTROPHY
Anaerobic fermentation (primitive)
glucose ->pyruvate -> ethyl alcohol + CO2 + heat +2 energy
Aerobic respiration (advanced)
glucose -> pyruvate -> H2O+CO2+heat + 36 units energy
AUTOTROPHY
Anoxic photosynthesis (primitive)
CO2 + H2S -> glucose + S
Oxygenated photosynthesis (advanced)
CO2 + H2O -> glucose + oxygen
Lecture 3:
The early earth and the origin of life
3. When could life have evolved?
When did life evolve?
After 4.6 Ba, when Earth formed
After 4.0 Ba, when meteorite
bombardment stopped
After liquid water,
recorded in oldest sediments, 3.8Ba
Before isotopic fractionation
of carbon by RUBISCO
Before oldest fossils, 3.5 Ba
Types of life
1. Multicelled
animals
(metazoans)
3. Eukaryotes
5. A hypothetical
minimum cell
2. Multicelled
plants
4. Prokaryotes
6. Replicating
molecules
How to study the origin of life
Interaction with atmosphere
Grades of organisation
- simplest modern life
What life needs
Fossils
= likely narrative
+ likely chronology
Prokaryote
Small, usually
anaerobic metabolism,
protected from UV,
short life
Eukaryote
Large, aerobic,
damaged by UV,
longer life
The phylogeny of early life
Lecture 3:
The early earth and the origin of life
4. Indirect evidence for life
Indirect evidence for life
A. Evidence for O2
Banded iron formations 3.5-1.8 By
Pyrite conglomerates 2.8 - 2.0 By
B. For photosynthesis
Isotopically ‘light’ carbon (more carbon-12 than
would be expected in abiotic situation)
Isua rocks slightly light (3.8 Ba)
All carbonates < 3.5 Ba very light
Lecture 3:
The early earth and the origin of life
5. The oldest fossils
The oldest fossils
Oldest fossils 3.5 Ba (for last decade)
1. Onverwacht Group (Swaziland Supergroup), South
Africa
2. Warrawoona Group (Pilbara Supergroup), Western
Australia
Cell chain
Stromatolites
Both Prokaryotes
Nb Biological evidence suggests split between
prokaryotes and eukaryotes at about 3.8 Ba
Early fossils: stromatolites
Living
prokaryotes
Precambrian
prokaryotes
Lecture 3:
The early earth and the origin of life
6. Biotic effects on surface processes
CO2 reservoirs for long timescales
Carbonate
carbon
Burial
Organic carbon
Weathering Land
Atmosphere 750
biotaWarm surface ocean
Cold surface ocean
850
550
150
Soils andIntermediate and deep waters
38000
detritus
Weathering
1500
Time, O2, rocks
and life
O2 and ozone shield
as Fe runs out
Fe absorbs O2
Time, O2, rocks
and life
Eukaryotes
Prokaryotes
Narrative of origin and
evolution of life
Ba
4.55 Earth forms
4.00 Meteorites subside
molecules replicate
minimum cell appears
photosynthetic prokaryotes
3.8 Oldest sediments
limited diversification
3.5 Oldest fossils
prokaryotes dominate
eukaryotes rare
2.1 Oldest large cell
- subject of next lecture