Evgenii V. Sharkov Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry (IGEM), Russian Academy of Sciences Moscow, [e-mail]

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Evgenii V. Sharkov Institute of Geology of Ore
Deposits, Petrography, Mineralogy and
Geochemistry (IGEM), Russian Academy of Sciences
Moscow, sharkov_at_igem.ru

• DEVELOPMENT OF GEOLOGICAL PROCESSES ON THE EARTH
  AND THEIR IMPACT TO THE EARLY BIOSPHERE

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It is known that the Earths ecological systems
in the Middle Paleoproterozoic were subjected to
essential changes, which promoted to acceleration
of the biosphere expansion and development.
Though life has been already existed in the
Paleoarchean Schidlowski, 1988 Westall and
Folk, 2003 De Grigorio et al., 2009 Fliegel et
al., 2010, the multicellular organisms appeared
only in the Paleoproterozoic Rozanov, Astafieva,
2009. What was occurred with ecological systems
and why? What was a trigger for such changing?
We try to answer on these questions using complex
of geological, petrological and geochemical
data.First of all I would like to remind you of
the general points of the Earths evolution,
including problem of the primordial crust,
because it was the basement for being and
development of the primitive biosphere

• .

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Problem of the primordial Earths crust

• According to modern models, this crust
  could be basic or sialic in composition. Both
  models require a global melting of a primary
  chondritic material for formation of the
  primordial crust. Due to theory of
  solidification, hardening of such magma ocean had
  to proceed upwards and resulted in accumulation
  of low-temperature derivates of granite
  composition at the surface as the primordial
  crust.
• Geological data, namely
  granite-dominated Archean crust, and data from
  the study of inherited zircon cores (Valley et
  al., 2002 Harrison et al., 2005) supports the
  primordial-sialic Earths crust hypothesis. The
  most suitable pretender for role of the
  primordial crust are plagiogranites (TTG series),
  which are composed about 85-90 of the Archean
  crust.

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Proper geological evolution of the Earth,
according to our data (Sharkov, Bogatikov, 2010),
can be subdivided on three major stages (1)
Nuclearic, lasted from ca. 4 Ga to ca. 2.7 Ga,
ie, practically all Archean (2) Cratonic, or
Transitional from ca. 2.7 till 2.0 Ga(3)
Continental-Oceanic, from 2.0 Ga till now.
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TECTONOMAGMATIC PROCESSES IN THE ARCHEAN AND
EARLY PALEOPROTEROZOIC

• Geological situation then was rather different
  from Phanerozoic. Granite-greenstone terranes
  (GGTs) and their separating granulite belts were
  the major Archean tectonic structures.
• The GGTs, consisting of irregular network of
  greenstone belts (not more 10-15 of area) among
  plagiogranite-gneiss (TTG) matrix, likely,
  strongly reworked primordial sialic crust.
  Mantle magmatism was represented by by high-Mg
  lava flows. Such magmas were derived from mantle
  sources, depleted by easily-melted components as
  a result of the primordial crust formation.
  Sediments played subordinate role.
• Archean structure of the Fennoscandian Shield
• 1- granite-greenstone terranes 2 greenstone
  belts3 reconstructed greenstone belts 4
  transitional Belomorian mobile belt 5-6 -
  granulite complex 7 middle Paleoproterozoic
  Svecofennian orogen 8 geological boundaries

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Ecological situation in Archean

• Biosphere could appear only after solidification
  of global magma ocean and appearance of liquid
  water. The first evidence of cyanobacterias being
  on the Earth were found in rocks of the Isua
  complex (3.8 Ga), where underwater pillow lavas
  widely developed (Rollinson, 2007 and references
  herein). Instead of the Phanerozoic, Archean
  oceans had relatively shallow depths and their
  floor was not composed by basalts.
• Presence in Archean sediments of detrital
  pyrite, uraninite, siderite, etc. testifies that
  Archean atmosphere was rather differ from the
  modern. It was reducing media, composed mainly by
  N2 and CO2 ??2 was very low and oceanic water
  was subacid (Krupp et al., 1994). Localities of
  primitive life in the Archean usually developed
  near hot springs on sea floor (Harris et al.,
  2009 De Grigorio et al., 2009) or in glassy
  crusts of lava flows (Furnes et al., 2004
  Fliegel et al., 2010).

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CARDINAL CHANGE IN THE EARTHS TECTONOMAGMATIC
EVOLUTION
Cardinal change in character of magmatism
occurred within period from 2.35-2.4 to 2.0 Ga
the early Precambrian high-Mg magmas, derived
from depleted mantle, gave place to the
geochemically-enriched Fe-Ti picrites and
basalts, similar to the Phanerozoic within-plate
magmas (Sharkov, Bogina, 2009). We believe that
ascending of the second generation mantle plumes
(thermochemical plumes), was responsible for
appearance of such magmas. Those plumes were
generated at the core-mantle boundary in D" layer
and this process is active till now (Dobretsov,
2008). The thermochemical plumes are enriched
in fluid components and their heads extended on
shallower level it resulted in crust fracturing,
oceanic spreading, formation and movement of
plates, subduction, etc., ie, appearance of the
plate tectonics. It was occurred at the
boundary of ca.2 Ga, and ancient primitive plume
tectonics was replaced by plate tectonics, and
the Earth entered at the Continental-oceanic
stage of its evolution.
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• So, since 2 Ga tectonomagmatic processes
  irretrievably changed over the whole Earth. As a
  result, ancient continental (sialic) crust became
  gradually replaced for secondary oceanic
  (basaltic) crust. Sialic crust, jointly with
  young basaltic crust has involved in subduction
  process and stored in the slab graveyards in
  the deep mantle .
• As a result, composition of the hard Earths
  surface was cardinally changed instead of
  predomination of sialic (granitic) rocks, mafic
  (basaltic) oceanic crust has quickly growed up,
  and now it forms about 60 of the present-day
  Earths crust.
• System volcanic arc-backarc sea (Sharkov and
  Bogatikov., 2010)
• 1 - asthenosphere 2 - lithosphere mantle
  beneath (a) continent, (b) ocean 3 upper mantle
  beneath discontinuity at 430 km (4) mantle
  beneath disconti-nuity at 680 km (5) lower crust
  (a) continental, (b) oceanic 6 - continental
  crust 7 - mixture of sialic and basic crustal
  material in subduction zone 8 - magma-generation
  zones (I tholeiite, II boninite, III
  calc-alkaline) 9 - direction of asthenosphere
  moving.

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Modern pattern of convergent margins according to
seismic tomography (Karason, van der Hilst,
2000).Blue subducted crust (both oceanic and
continental)
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• New type of magmas was characterized by elevated
  and high contents of Fe, Ti, Cu, P, Mn, Na, K,
  LREE, and some rare elements (Zr, Ba, Sr, U, Th,
  F, Cl, etc.).
• Large-scale influx of alkalis in the World Ocean
  presumably neutralized its water, making it more
  suitable for life, while input of Fe-group
  metals, P, alkalis, Cl and other elements, which
  are required for metabolism and fermentation,
  rapidly expanded the possibility for the
  development of biosphere. Judging on appearance
  of oxidative atmosphere ca. 2.3 Ga (Great
  Oxidation Event) Melezhik et al., 2007, 2012
  Guo et al., 2009), it promoted especially to
  explosion of photosynthesizing organisms.
• The manifestation of this geochemically enriched
  magmatism was correlated with the first finds of
  eucaryotic heterotrophic organisms at 2 Ga, for
  example in black shales and phosphorites of the
  Paleoproterozoic Pechenga complex, Kola Peninsula
  Rozanov, Astafieva, 2008. For instance, a
  significant increase in amount of spheromorphides
  and remains of filamentous algae is observed in
  the Upper Jatulian deposits ( 2.0 Ga) of Karelia
  Akhmedov, Belova, 2009. The vital activity of
  the organisms led to significantly increasing the
  oxygen content in atmosphere, which was marked by
  the formation of cupriferous red beds at all
  Precambrian shields, generation of the first
  hydrocarbon deposits (shungites, Karelian craton)
  Melezhik et al., 2005, rock-salt in Karelia
  Morozov et al., 2010, and phosphorites with
  age of 2.06 Ga on the Indian and Kola cratons
  Melezhik et al., 2005.

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• Thus, a fundamental change in character of
  tectonomagmatic activity acted as the trigger for
  environmental changes and acceleration of
  biospheric evolution, supplying a qualitatively
  new material on the Earths surface. This event
  gave impetus to wide expansion of biosphere,
  which fixed by beginning of oxidative atmosphere,
  change of Sr isotopy in sedimentary carbonates,
  and enhanced biosphere mass as demonstrated by
  appearance of hydrocarbon deposits.
• However, rapid enhanced of the bulk of biosphere
  did not accompanied by the same increasing of the
  biodiversity new forms (especially multicellular
  organism) appeared in small quantity and long
  time did not essential developed.

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Situation on Venus and Mars

• Data available on Venus and Mars suggest that
  their tectono-magmatic evolution also occurred at
  the close scenario (Sharkov, Bogatikov, 2009 and
  references herein). Two major types of
  morphostructures, which are vast plains, composed
  by young basaltic crust, and older lightweight
  uplifted segments with a complicated topography
  can evidence about two-stage evolution of these
  planets. If we dry the modern Earths oceans, we
  will see the same picture.

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• Presence of drainage systems on Mars and valleys
  on Venus assumes existence of liquid water on
  early stages of their development. Like on the
  Earth, red beds appeared on the Mars at the
  middle stage of its evolution, and may be at
  this period photosynthesizing microorganisms
  existed on Mars (McKay et al., 1996). Powerful
  eruptions of gigantic volcanoes of Tharsis and
  Elysium, probably, led to fall of temperature and
  disappearance of liquid water on Mars which
  terminated biosphere evolution.
• In contrast to Mars, on Venus speeded up
  greenhouse effect appeared, which led to dry and
  very hot surface, unfavourable for life also.
• So, processes of the planetary evolution were
  favourable for the biosphere development only on
  the Earth.

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CONCLUSIONS

• The primordial Earths crust was likely granitic
  in composi-tion. Tectonomagmatic activity on
  Earth in Archean and early Paleoproterozoic) was
  rather different from Phanero-zoic the major
  tectonic feature were granite-greenstone terranes
  where plagiogranites composed 85-90 territory
  and high-Mg volcanics, derived from depleted
  mantle sources, predominated in greenstone belts.
• A drastic change of the tectonomagmatic and
  ecology processes on Earths surface occurred in
  the Middle Paleo-proterozic, ca. 2.35-2.0 Ga,
  when new type of magmas appeared. It was
  characterized by elevated and high contents of
  Fe, Ti, Cu, P, Mn, alkalis, LREE, and other
  elements (Zr, Ba, Sr, U, Th, Cl, etc.), which are
  required for metabolism and fermentation, rapidly
  expanded the possibility for the development of
  biosphere. A large-scale influx of alkalis in the
  World Ocean presumably neutralized its water,
  making it more suitable for the life

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• 3. Fundamental changes in tectonomagma-tic
  activity acted as a trigger for environ-mental
  changes and biosphere evolution, supplying a
  qualitatively new material to the Earths
  surface.
• 4. Venus and Mars developed at the same scenario
  very likely, that at the beginning liquid water
  occurred on them however, processes of the
  planetary development were favourable for the
  biosphere evolution only on the Earth.

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THANK YOU!