Geobiology and the history of life II
The story of oxygen
The rise of Eukaryotes
Sustaining life on the planet
• All organisms derive energy for growth by moving
electrons from a substrate to a product
• All substrates and products must ultimately be
cycled
• Biological processes are paired eg photosynthesis
and respiration
Sustaining life on the planet
• All metabolic processes are microbial and originated
in the Archaen and Proterozoic Eons
PreCambrian
(1.Achaen and 2. Proterozoic)
4600mya
3500mya
Origin of earth Origin of life
5. Cenozoic
3. Paleozoic
4. Mesozoic
2500mya
Accumulation
of atmospheric
oxygen
600mya
Soft bodied
invertebrates,
diverse algae
The big six
•
The origin of life is the invention of non-equilibrium redox
chemistry that involves five of the “big six”
• H, C, N, O, P, S
• And at least 54 trace elements
• Oxidation is loss of electrons.
• Reduction is gain of electrons.
Biological processes are paired
• Oxygenic photosynthesis (Photosynthesis II)
•
2H20 + C02 ---->(CH20)11+O2
• Respiration reaction
•
(CH2O)11 + O2 ----> CO2 + 2H2O
Organic Carbon in surface sediments
• Organic carbon in surface sediments
G. Peneplaned Mountain
F. Collison orogengy
A. Stable craton
E. Closing remnant
Ocean Basin
B. Early Rifting
D. Subduction Zone
C. Full Ocean Basin
How Ancient Bacteria Changed the World
• Fossilized mats of prokaryotes
2.5 billion years old
•
microbrial communities are
called stromatolites
Photosynthesis on tree of life
•
Universal phylogenetic tree based on comparative sequence
data from 16S or 18S ribosomal RNA.
•
•
•
Red = hyperthermophilic species
lavender = anoxygenic photosynthetic species
green = oxygenic photosynthetic species
Divergence of prokaryotes
Hydrogen-Rich Anaerobic
Atmosphere
Oxygen in
Atmosphere
Archae
(live in extreme
environments)
Genetic info & complexity increases
ANCESTORS OF
EUKARYOTES
(fungi, plants,
Aerobic respiration evolves animals)
in many bacterial groups.
ORIGIN OF
PROKARYOTES
3.8 billion ya
3.2 billion ya
Photosynthetic
Bacteria
Other
Bacteria
2.5 billion ya
Endosymbiosis
possibly an alpha proteobacterium, closely related
to extant non-sulphur photosynthetic bacteria
Conditions for complex life
• Complex life tolerates a far narrower range of
environmental conditions than do microbes
• Complex life is far more susceptible to extinction
caused by short-term environmental deterioration
• On any planet, the number of mass extinctions may
determine where life arises and how long it lasts
• Earth is found in an area of low amounts of space
debris
Explanations for rise of Eukaryotes
Explanations for rise of Eukaryotes
• Snowball earth
•
•
•
•
atmosphere dominated by
Methane gas
appearance of oxygen
caused rapid decline in
temperature
freezing in the poles, earth
becomes reflective, whole
earth freezes over
Volcanic activity continues,
CO2 accumulates under ice,
greenhouse effect
Why oxygen is required for complex life
•
The reduction of oxygen provides the largest free energy
release per electron transfer, except for the reduction of
fluorine and chlorine.
•
The bonding of O2 ensures that it is sufficiently stable to
accumulate in a planetary atmosphere, whereas the more
weakly bonded halogen gases are far too reactive ever to
achieve significant abundance
•
Complex life has high energy demands – aerobic metabolism
•
An 02 atmosphere took about 600 million years to evolve
Catling et al. 2005
5. The Cambrian explosion
Paleozoic (= ancient life)
Cambrian
Carboniferous
535mya 495mya 439mya 408 mya 353mya
Algae
abundant
First land
plants
First
insects
First
jawed fish
290mya 251mya
First mammallike reptiles
First reptiles
All animal phyla
present
(A phylum is a taxonomic category above a class and below a kingdom. Members
of a phylum share a general body plan)
The Cambrian explosion
• Almost all animal phyla made
their first appearance in the
fossil record over a span of
just 40 million years
• Produced extreme
morphological diversity
Explanations for Cambrian explosion
• Environmental causes
Gondwana
shallow seas
(light blue)
Laurentia
The Earth during the Cambrian 540 mya
R. Damian Nance , J. Brendan Murphy
Origins of the supercontinent cycle
Geoscience Frontiers, Volume 4, Issue 4, 2013, 439 - 448
http://dx.doi.org/10.1016/j.gsf.2012.12.007