Geologic Evidence for the Antiquity of Life Readings on the Antiquity and Origin of Life
• :
Nature 409
Nature 417, 782-784.
Nature 416, 76-81.
• :
Nature 418
Nature 416, 73-76.
Science, 2891340.
Nature 410, 77-81. Science, 289
Assigned Reading
1. Stanley (1999), pp. 306-311 & 320-323
2. Nisbet, E.G. and N.H. Sleep (2001) “The habitat and nature of early life.” , 1083-1091.
3. Orgel, L.E. (1994) “The origin of life on Earth.” Scientific American, October 1994, 77-83.
4. Hazen, R.M. (2001) “Life’s rocky start.” Scientific American, April 2001, 77-85. 5. Dalton, R. (2002). “Squaring up over ancient life.” 6. Brasier, M. D., Green, O. R., Jephcoat, A. P., Kleppe, A. K., Van Kranendonk, M. J., Lindsay, J. F.,
Steele, A., and Grassineau, N. V. (2002). “Questioning the evidence for Earth's oldest fossils.”
Suggested Reading
1. van Zuilen, M. A., A. Lepland and G. Arrhenius (2002). “Reassessing the evidence for the earliest traces of life." : 627-630.
2. Chyba and Sagan, 1996, “Comets as a source of Prebiotic Organic Molecules for the Early Earth” in Comets and the Origin and Evolution of Life (Eds Thomas, P.J., Chyba, C.F., McKay, C.P.)
3. Schopf, J. W., Kudryavtsev, A. B., Agresti, D. G., Widowiak, T. J., and Czaja, A. D. (2002). “Laser-Raman imagery of Earth's earliest fossils.”
4. Cody, G.D., Boctor, N.Z., Filley, T.R., Hazen, R.M., Scott, J.H., Sharma, A. & Yoder Jr., H.S. (2000) Primordial carbonylated iron-sulfur compounds and the synthesis of pyruvate. , 1337-
5. Shen Y. and Canfield D. E. (2001) isotopic evidence for microbial sulphate reduction in the early Archaean era.
6. Wächtershäuser, G. (2000) Life as we don't know it. , 1307-1308.
Early Earth History
Antiquity of Life
•The lost record of the origin of Life. It happened >3.5 Ga
–Oldest terrestrial rocks 3.98 Ga (Bowring, MIT) and cooked
Summary of Geologic Evidence for the
–Oldest minerals – zircons 4.2 Ga
–Oldest microfossils – Warrawoona (Pilbara Craton) 3.5 Ga are contentious because of sedimentary relationships –Next oldest known & convincing microfossils from a hydrothermal vent in Western Australia’s Pilbara craton 3.2 Ga –Oldest molecular fossils (“biomarkers”)-2.7 Ga (Brocks et al)
Origin and Early Evolution of Life • The lost record of the origin of Life? Few crustal rocks from >3
Ga and half life of sediments 100-200Ma so most destroyed
d 13
C
Corg
Ccarb
Span of
modern values
autotrophs
sediments
4 0.5
Time Ga
Carbon Isotopic Evidence for Antiquity of Life
2.5
Science
•Re-mapping of Akilia Island & new petrologic & geochemical
(not BIFs).
their formation.
Akilia Island, SW Greenland 13C-depleted graphite
•Rocks interpreted to be sedimentary (Banded Iron Formations--BIFs).
precipitation and settling out of particles from seawater. •Critical indicators of early life b/c they establish existence of liquid hydrosphere in a habitable T range.
Geology Matters: 1
Fedo & Whitehouse (2002) , Vol. 296:1448-1452.
analyses do not support sedimentary origin for these rocks. •They appear instead to be metasomatized ultramafic igneous rocks
•Therefore highly improbable that they hosted life at the time of
•Evidence for life >3.85 Gyr ago from
•BIFs formed early in Earth’s history, supposedly by chemical
Science
•Quartz-pyroxene outcrop originated as igneous rock, compositionally modified during repeated episodes of
pyroxene, amphibole) •Deformational petrologic features inconsistent with BIF
Geology Matters: 2
See the images by Fedo & Whitehouse , Vol. 296 (2002): 1448-1452.
metasomatism & metamorphism (lt = quartz; dk =
Geology Matters: 3
Science,
•REE pattern, elemental ratios & mineralogy all consistent with Akilia
See the figures by Fedo & Whitehouse Vol. 296 (2002): 1448-1452.
igneaous rocks, not BIFs
•Geochemical evidence against Akilia rocks being BIFs
protolith secondary, metasomatic isotopic systematics
Ga Isua Supracrustal most metasomatic rocks
metacarbonate
by Schidlowski Mojzsis Ga .
d13
2 or CH4
AGU, 82(Lepland, A., van Zuilen, M., Arrhenius, G) The principal method for studying the earliest traces of life in the metamorphosed, oldest (> 3.5 Ga) terrestrial rocks involves determination of isotopic composition of carbon, mainly prevailing as graphite. It is generally believed that this measure can distinguish biogenic graphite from abiogenic varieties. However, the interpretation of life from carbon isotope ratios has to be assessed within the context of specific geologic circumstances requiring (i) reliable interpretation (ii) control of
processes, and (iii) understanding of different graphite producing mechanisms and related carbon . We have carried out a systematic study of abundance, isotopic composition and petrographic associations
of graphite in rocks from the ca. 3.8 Belt (ISB) in southern West Greenland. Our study indicates that of the graphite in ISB occurs in carbonate-rich (metacarbonates) while sedimentary units, including banded iron formations (BIFs) and metacherts, have exceedingly low graphite concentrations. Regardless of isotopic composition of graphite in rocks, their secondary origin disqualifies them from providing evidence for traces of life stemming from 3.8 Ga. Recognition of the secondary origin of Isua metacarbonates thus calls for reevaluation of biologic interpretations
et al. (1979) and et al. (1996) that suggested the occurrence of 3.8 biogenic graphite in these rocksThe origin of minute quantities of reduced carbon, released from sedimentary BIFs and metacherts at combustion steps > 700°C remains to be clarified. Its isotopic composition ( C = -18 to -25‰) may hint at a biogenic origin. However, such isotopically light carbon was also found in Proterozoic mafic dykes cross-cutting the metasedimentary units in the ISB. The occurrence of isotopically light, reduced carbon in biologically irrelevant dykes may indicate secondary graphite crystallization from CO
- containing fluids that in turn may derive from bioorganic sources. If this were the case, trace amounts of isotopically light secondary graphite can also be expected in metasediments, complicating the usage of light graphite as primary biomarker. The possibility of recent organic contamination, particularly important in low graphite samples, needs also to be considered; it appears as a ubiquitous component released at combustion in the 400-500°C range. A potential use of the apatite-graphite association as a biomarker has been proposed in the study by Mojzsis et al. (1996). Close inspection of several hundred apatite crystals from Isua BIFs and metacherts did, however, not show an association between these two minerals, moreover graphite is practically absent in these metasediments. In contrast, apatite crystals in the non-sedimentary metacarbonate rocks were found commonly to have invaginations, coatings and inclusions of abundant graphite. Considering that such graphite inclusions in apatite are restricted to the secondary metasomatic carbonate rocks in the ISB this association can not be considered as a primary biomarker in the Isua Supracrustal Belt References: Mojzsis,S.J, .Arrhenius,G., McKeegan, K.D.,.Harrison, T.M.,.Nutman, A.P \& C.R.L.Friend.,1996. Nature 384: 55 Schidlowski, M., Appel, P.W.U., Eichmann, R. & Junge, C.E., 1979. Geochim. Cosmochim. Acta 43: 189-190.
Tracing Life in the Earliest Terrestrial Rock Record, Eos Trans. (47), Fall Meet. Suppl., Abstract P22B-0545 , 2001
Know Thy Rock: 1
Nature (2002): 627-630.
•Carbonate in occurs in 3 distinct phases •Likely formed during multiple injections of fluid
and their host rocks.
See Figure 1 by Van Zuilen et al. Vol. 418
3.8 Ga Isua (SW Greenland) rocks
across contacts between igneous ultramafic rocks
Know Thy Rock: 2
Nature Vol. 418 (2002): 627-630.
rocks.
6FeCO3 --> 2Fe3O4 2 + C
introduction of elements into rock by circulating fluids
See Figure 3 by Van Zuilen et al.
•Graphite is associated primarily with the metacarbonate rocks, NOT with metasedimentary
•This suggests the reduced carbon formed by thermal disproportionation of the carbonates. E.g.,
+ 5CO
Metasomatism:
Know Thy Rock: 3
Nature Vol. 418 (2002): 627-630.
•Most of the reduced C does not have the large 13C-depletion expected from biological materials.
See Figure 2 by Van Zuilen et al
•Most of the reduced C (graphite) in the 3.8 Ga Isua rocks is in the metacarbonate phases and not the metasedimentary phases & likely formed by thermal disproportionation of the carbonate minerals at a later time.
•The isotopically-depleted C is only found in the metasedimentary rocks, where it’s concentration is very low & it may be contamination….
Know Thy Rock: 4
Nature Vol. 418 (2002): 627-630.
(of presumed biological origin) combusts at low T,
material (I.e., contamination)
See Figure 4 by Van Zuilen et al.
•The isotopically-depleted C in this 3.8 Ga Isua sample
suggesting it is unmetamorphosed recent organic
Biogenic Origin of Reduced Carbon in
Nature Vol. 418:627-630.
Bottom Line: No evidence for a
3.8 Ga Isua (SW Greenland) Rocks
Van Zuilen et al (2002)
autotrophs
d 13
C
Corg
Ccarb
Span of
modern values
sediments
4 0.5
Time Ga 2.5
Revised C Isotope Evidence for Life’s Antiquity
With the carbon isotopic evidence for life >/= 3.8 Ga now seriously challenged….
It’s time to look at some fossil evidence for early life….
But don’t be surprised to find plenty of controversy there too!
So jump ahead 300 Myr to 3.5 Ga…
See Figure 1 by Schopf et al. Nature, vol. 416 (2002): 73-76.
•Photo-montages of inferred microfossils from rocks ranging in age from 0.7-3.5 Ga.
Schopf’s Apex ‘microfossils’ #1
See the image by Gee Nature, 416 (2002): 28, and Nature, 416 (2002): 76-81.
Non-biologic Origin of 3.5 Gyr
Brasier et al.
•Schopf’s “microfossils” seem to have formed hydrothermally (hot water + rock)
“Microfossils”?
Questioning the authenticity of 3.465 Ga Apex fossils: 1
See Figure 1 by Brasier et al. Nature, Vol. 416 (2002): 76-81.
•Rather than emanating from a sedimentary rock,
hydrothermal rock vein created by the interaction of hot rock + H2O
the Schopf ‘microfossils’ came from a
Questioning the authenticity of 3.465 Ga Apex fossils: 2
See Figure 2 by Brasier et al. Nature, Vol. 416 (20020: 76-81.
“Many of these filamentous structures [from
ways not shown in the original descriptions because of the choice of focal depth and/or
the apex chert] are branched or formed in
illustrated field of view.”
Questioning the authenticity of 3.465 Ga Apex fossils: 3
See Figure 2 by Brasier et al. Nature, Vol. 416 (2002): 76-81.
•It would appear as though Schopf (1993) “left out” some essential morphological features of his ‘microfossils’…
See Figure 3 by Schopf et al. Nature(2002): 73-76.
•Indicates presence of reduced carbon (graphite)
Schopf’s ‘microfossils’ #2: Raman Spectroscopy to the rescue?
, vol. 416
•Raman spectra & spectral maps (G band) of 0.7-3.5 Ga ‘microfossils’
associated with ‘microfossils’.
Questioning the authenticity of 3.465 Ga Apex fossils: 4
See Figure 4 by Brasier et al. Nature, Vol. 416 (2002): 76-81.
•The spectroscopic results therefore provide no support
•Unfortunately for Schopf et al., Raman spectra of dark specks within surrounding host (quartz) rock of Apex ‘microfossils’ give same Raman spectrum.
for the “biogenicity” of Schopf’s ‘fossils’.
structures #1
•Morphology is at best an ambiguous indicator of
•Evidenced here by inorganic aggregates precipitated from a simple solution of BaCl2, Na2SiO3, NaOH
See the images by Garcia Ruiz et al. Astrobiology, Vol. 2(3) (2002): 353-369.
Abiotic origin of microfossil-like
biogenicity.
So… morphology can be be a poor indicator of biogenicity.
As can Raman spectrospcopy.
And carbon isotopes.
Yet our quest for for evidence of life 3.5 Ga does not end here.
We need to take a look at… Stromatolites.
Stromatolites-1
Stromatolites are fossils which show the life processes of
domes. Ozarkcollenia, a distinctive type of layered
cyanobacteria (fomerly called blue-green algae). The primitive cells (Prokaryotic type), lived in huge masses that could form floating mats or extensive reefs. Masses of cyanobacteria on the sea floor deposited calcium carbonate in layers or domes. These layered deposits, which have a distinctive "signature" are called laminar stromatolites. This is an example of a layered stromatolite from the Ozark Precambrian. Most often, stromatolites appear as variously-sized arches, spheres, or
Precambrian stromatolite, pushes the appearance of life in the Ozarks to well over 1.5 Ga.
Stromatolites-2
does today.
Stomatolites are colonial structures formed by photosynthesizing cyanobacteria and other microbes. Stromatolites are prokaryotes (primitive organisms lacking a cellular nucleus) that thrived in warm aquatic environments and built reefs much the same way as coral
stromatolites?
Nature, 382, 423-425, October 3, 1996.
•Seems statistically feasible that the morphology of
processes.
A possible abiotic origin for
Grotzinger, J. and Rothman, D.H., “An abiotic model for stromatolite morphogenesis,”
stromatolites can occur through non-biological
Modern Living StromatolitesAustralia
between microbes, other biological influences and the physical and chemical environment.
mucus that each cell secretes, then bind the sediment grains
light, their growth keeps pace with the accumulating sediment.
: Shark Bay,
•Hamelin Pool’s stromatolites result from the interaction
•The cyanobacteria trap fine sediment with a sticky film of
together with calcium carbonate which is separated from the water in which they grow. Because the cyanobacteria need sunlight to grow and they have the ability to move towards
The majority view seems to be that
life, placing its origin in the vicinity of 3.5 Ga.
depleted sulfur minerals….
stromatolites are the first good evidence for
By 3.47 Ga there is additional evidence for microbial life in the form of isotopically-
Microbial Activity ~3.47 Ga Suggested by Sulfur Isotopes
See the image by Shen et al. Nature, Vol. 410 (2001): 77-81)
SO4 2- + 2CH2O = S2- + 2CO2 + 2H2O
Microbial sulphate reduction?
Australia).
Only this time it did not form at the
Rather microbial life seems to have evolved in a submarine thermal spring system…
By 3.5 Ga then there is evidence for life from stromatolites (Warrawoona, NW Australia) & isotopically-depleted sulfur in barite (N. Pole,
By 3.2 Ga there is new and different evidence for life…
surface….
excellent evidence for both microbial life,
eukaryotes & oxygenic
molecular fossils.
By 2.7 Ga there is
photosynthesis from
Warrie
Mem
ber
Roy H
ill Sh
ale M
emb
erJeerin
ah
Form
atio
nM
arra
Mam
ba F
orm
atio
nM
ad
din
aF
m.
min20 30 40 50
min20 30 40 50
Ham
ersley G
rou
p
Fortescu
e Gro
up
Roy4
Pyritic Sandstone
Roy6
Fibrous Quartz
War1
Black Chert TOC = 0.5%
Mad1
Basalt
Mam1
Black Shale TOC = 2.6%
Roy1
Black Shale TOC = 7.4%
Roy2
Black Shale TOC = 8.6%
Roy5
Black Shale
Roy3
Black Shale TOC = 9.0%
Low TOC High TOC
nC20nC14
660
670
680
690
700
710
720
776
780
Summons, Brocks, et al.
•GEOCHEMISTRY vs STRATIGRAPHY
Steranes Hopanes
C27 100%
C28 26%
C29 33%
C30 5%
Diasteranes
C27 50%
Me-C31 12%
C31 26%
C30 55%
C29 100%
Ts
Tm
22S 22R
2a-Methyl-
Time (min)54 58 62 646056
•
Summons, Brocks, et al.
Regular Steranes
ab
ab
ab
BIOMARKERS BY GC-MS-MS
•
potentially useful for studying the early biological record.
• Hydrocarbons often abundant in Sometimes accumulate massively ie petroleum reservoir.
•
Hydrocarbons
Hydrocarbons, the remains of lipids from once living organisms, are rich in information and
sediments.
Hydrocarbons are mobile. Need to establish
indigeneity / syngeneity ?
OHOH
2HO
HO
OH
OHOH
H
H
H
H
H
skeleton
and 13C content
•
R. Summons
Absolute requirement for O in biosynthesis
preservation of
Recalcitrance of Hydrocarbons
• Are recalcitrant, have distinctive
structures that are diagnostic for:
– type of microbe
– their physiological processes &
– environments they inhabit
Hydrocarbons
bacteria
cyanobacteria MM
M
H
M
M
1 2 3
4 M
BACTERIA
EUCARYA
ARCHAEA
Thermocrinis
Aquifex
Thermotoga
OH
OH
OH
OH
O
O
OH
HO
>2.7 Ga
>2.7 Ga
R
R. Summons (data)
man animals
fungi flagellates
diplomonads
micros poridia plants
ciliates slime molds
green sulfur
gram positives
protcobacteria
avobacteria
Sulfolobus
Des ulfurococcus
Pyrodictium
Thermofilum Thermoproteus
Pyrobaculum Pyrococcus
ethanobacterium ethano-thermus
ethanoplanus
Archaeoglobus alococcus
Halobacterium
ethanosarcina
Methanospirillum ethanopyrus
ethanococcus 1 jannaschii
4 vanniellii
2 igneus 3 thermolithotrophicus
Parallel Molecular Signatures
Black Chert Breccia
Black Chert vein
A Typical Banded Iron Stone (BIF)
Complexity of Extant LifeSpecies Type Approx. Gene Number
Prokaryotes
E. Coli typical bacterium 4,000
Protists
O. Similis
S. Cerevisiae
Distyostelium discoideum
protozoan
yeast
slime mould
12,000-15,000
7,000
12,500
Metazoan
C. Elegans Nematode 17,800
D. melanogaster Insect 12,000-16,000
S. Purpuratas Echinoderm <25,000
Fugu rubripes Fish 50,000-10,0000
Mus musculus Mammal 80,000
Homo sapiens mammal 60,000-80,000
After Maynard-Smith and Szathmary, 1999
Major Transitions in Origin/Evolution of Lifereplicating molecules populations of molecules in protocells
independent replicators chromosomes
RNA as a gene and enzyme DNA genes, protein enzymes
prokaryotic cells Cells with nuclei & organelles ie eukaryotes
asexual clones sexual populations
single bodied organisms fungi, metazoans and metaphytes
solitary individuals colonies with non-reproductive castes
primate societies human societies with language
After Maynard-Smith and Szathmary, 1999
*
Q: A: N = Ng fp ne fl fi fc fL ~ 1,000
Ng=# of stars in our galaxy ~ 4 x 1011 (good) fp 0.1 (v. poor) ne 0.1 (poor) fl=fraction of habitable planets on which life evolves fi=probability that life will evolve to an intelligent state fc
long distances fl fi fc ~ 1/300 ( ) fL
technological civilization ~ 1 x 10-4 (v. poor)
*
which we might one day establish radio communication.
The Drake EquationWhat is the possibility that life exists elsewhere?
=fraction of stars with planets ~ =# of Earth-like planets per planetary system ~
=probability that life will develop capacity to communicate over C. Sagan guess!
=fraction of a planet’s lifetime during which it supports a
An estimate of the # of intelligent civilizations in our galaxy with