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DEVELOPMENT OF
GEOLOGICAL PROCESSES
ON THE EARTH AND THEIR
IMPACT TO THE EARLY
BIOSPHERE
Evgenii V. Sharkov
Institute of Geology of Ore Deposits, Petrography, Mineralogy
and Geochemistry (IGEM), Russian Academy of Sciences
Moscow, [email protected]
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It is known that the Earth’s 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
Earth’s 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 Earth’s 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 granitedominated Archean crust, and data
from the study of inherited zircon cores
(Valley et al., 2002; Harrison et al., 2005)
supports the primordial-sialic Earth’s
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.
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.
TECTONOMAGMATIC PROCESSES
IN THE ARCHEAN AND EARLY PALEOPROTEROZOIC
Geological situation then was rather
different from Phanerozoic. Granitegreenstone 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 plagiogranitegneiss (TTG) matrix, likely, strongly
reworked primordial sialic crust. Mantle
magmatism was represented by by highMg 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 belts;3 – reconstructed
greenstone belts; 4 – transitional Belomorian mobile belt; 5-6 granulite complex; 7 – middle Paleoproterozoic Svecofennian orogen; 8
– geological boundaries
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; РО2 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).
CARDINAL CHANGE IN THE EARTH’S
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.
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
Earth’s 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 Earth’s 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 discontinuity 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 - magmageneration zones (I – tholeiite, II – boninite, III – calcalkaline); 9 - direction of asthenosphere moving.
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].
• 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
Earth’s 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.
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 Earth’s oceans, we will see
the same picture.
• 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 it’s
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.
CONCLUSIONS
1. The primordial Earth’s crust was likely granitic in composition. Tectonomagmatic activity on Earth in Archean and
early Paleoproterozoic) was rather different from Phanerozoic: 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.
2. A drastic change of the tectonomagmatic and ecology
processes on Earth’s surface occurred in the Middle Paleoproterozic, 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
• 3. Fundamental changes in tectonomagmatic activity acted as a trigger for environmental changes and biosphere evolution,
supplying a qualitatively new material to the
Earth’s 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!