Early Life on Earth

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EPSC 205B - Astrobiology
Early Life on Earth Hans Hofmann Redpath Museum
and Dept. of Earth and Planetary Sciences McGill
University Montreal, QC
February 2009
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Primitive life on Earth
Evidence for ancient life
- What are we looking for?
- What is evidence? Types of fossils
- What is evidence?
- Where do we find evidence? Fossils from deep
time occur in Precambrian rocks
- Where do we find evidence?
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1820-1899
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HJH00
Structure studied by Wm. Dawson in 1860s Eozoon
canadense, Precambrian marble, Cote St-Pierre, QC
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Precambrian outcrop areas of the world (most
areas are underlain by crystalline rocks)
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1000 km
Areas of Precambrian outcrop
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Precambrian fossils
How do we know that the remains are biogenic ?
What types of remains are preserved ?
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CLASSIFICATION
(Hofmann, 1972, Int. Geol. Congr., Proc. Sect.
1., p. 20-30)
PSEUDO- FOSSIL
FOSSIL
DUBIOFOSSIL
abiogenic
biogenic
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Universal tree of life (Woese et al. 1990,
modified by Stetter 1993) (Stetter, in Bengtson,
ed. Early Life on Earth, p. 143-151)
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Types of Precambrian remains Hofmann 1987,
Geoscience Canada 14135-154
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Schopf 1993, Science 260640-646
Bacterial microfossils or artifacts? Western
Australia Warrawoona Group
Geon 34
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JW Schopf, PPRG
Possible microbial mat, Onverwacht Gp., Kromberg
Fm. (Geon 34), South Africa (Muir Grant, in
Windley, 1976)
Geon 34
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Kakabeka Cgl.
Archean greenstone
HJH slide 8996 9 Jun 1986
Schreiber Channel, N shore of Lake Superior, ON
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Greenstone boulder
Black chert with microfossils
HJH slide 9007
Gunflint Fm.
Geon 18
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Geon 18
Geon 27
Archean-Proterozoic section at Schreiber Channel,
N shore of L. Superior (Hofmann 1969, GSC Pap.
68-69)
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Carbonaceous microfossils in thin sections of
chert Gunflint Fm. (1.88 Ga) Schreiber,
ON (Hofmann Schopf 1983, in Schopf,
ed., Earths earliest biosphere, Photo 14-1)
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Stromatolite elements, Shark Bay, W.
Australia (Hofmann, 1973, Earth-Sci. Rev.
9339-373)
Microbial mat
Water
Oncolites
Sediment
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Stromatolite growth (Hofmann, 1969, GSC Paper
69-39)
Sunlight Water Minerals Substrate
1 organic layer
1 organic 1 mineral layer
growing stromatolite
fossil stromatolite
mound
Further growth compaction crystallization
induration partial burial
Cessation of growth decomposition burial
lithification
Colonization Rapid growth
Slow growth or influx of sediment or
precipitation Localized sediment accumulation
Periodic repetition
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S
S
S
slide 3654 25 Jun 73
Silicified microbial mats, Belcher Spgp.,
McLeary Fm., Sanikiluaq, Belcher Islands, NU
(Hofmann 1975, Am. J. Sci. 2751121-1132)
Geon 18
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50 µm
GSC 43589
Silicified microbial mats, Belcher Spgp.,
Kasegalik Fm., Belcher Islands, NU (Hofmann
1975, Am. J. Sci. 2751121-1132)
Geon 18
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Coniform stromatolites, Warrawoona Gp. Hofmann et
al., 1999, GSA Bull.
Geon 34
http//www.doir.wa.gov.au/GSWA/DE1D31DE791E4A8A8EE
560584052FB3F.asp
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10 µm
GSC 98912
Mesoproterozoic cyanobacterium Tetraphycus Society
Cliffs Fm., Baffin Id., Nunavut (Hofmann and
Jackson, 1991, J. Paleont. 65361-382, Fig. 10/7)
Geon 12
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Cyanobacteria
Cephalophytarion grande Bitter Springs Fm. (Geon
8), Ross River, NT, Australia (Schopf 1968, J.
Paleont., Pl. 106, fig 1)
10 µm
HJH slide 16 Dec 1975
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Diorama of composite Ediacaran biota, NMNH,
Washington
Geon 5
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Changes with geologic time Hofmann 2004, Redpath
Museum - Dawson Gallery