![A geochemical scenario illustrating the " Soda Ocean " hypothesis as the ocean evolved throughout Earth history (x-axis) (altered after Kempe and Kazmierczak, 1994). After the initial equilibration of water and CO 2 with volcanic silicates through weathering (Urey reaction), the ocean would have had a high carbonate alkalinity (lefthand scale) and a moderately high pH (right-hand side). Consequently, the total calcium concentration would have been low while the CaCO 3 supersaturation [top of graph with separate scale for calcite (Cc) supersaturation index] would have been very high (i.e., .0.8), above which spontaneous inorganic precipitation regulates Ca concentration. Because of the slow decrease of alkalinity in the ocean through subduction of seawater, the Soda Ocean would have lasted through much of geological history. The " Halite Ocean " would have prevailed for only the last 1 billion years. In the Phanerozoic sulfate reduction could have modulated ocean alkalinity, either globally or in isolated basins, owing to the development of anoxia in bottom waters [i.e., owing to the " alkalinity pump " (Kempe and Kazmierczak, 1994)]. The Cc saturation was then governed by biomineralization, which today keeps seawater at supersaturation lower than required for inorganic precipitation.](https://www.researchgate.net/profile/Stephan-Kempe/publication/11019243/figure/fig3/AS:434886533226496@1480696437037/A-geochemical-scenario-illustrating-the-Soda-Ocean-hypothesis-as-the-ocean-evolved_Q320.jpg)
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ASTROBIOLOGY
Volume 2, Number 1, 2002
© Mary Ann Liebert, Inc.
Hypothesis Paper
Biogenesis and Early Life on Earth and Europa:
Favored by an Alkaline Ocean?
STEPHAN KEMPE1and JOZEF KAZMIERCZAK2
ABSTRACT
Recent discoveries about Europa—the probable existence of a sizeable ocean below its ice
crust; the detection of hydrated sodium carbonates, among other salts; and the calculation of
a net loss of sodium from the subsurface—suggest the existence of an alkaline ocean. Alka-
line oceans (nicknamed “soda oceans” in analogy to terrestrial soda lakes) have been hy-
pothesized also for early Earth and Mars on the basis of mass balance considerations involving
total amounts of acids available for weathering and the composition of the early crust. Such
an environment could be favorable to biogenesis since it may have provided for very low
Ca21concentrations mandatory for the biochemical function of proteins. A rapid loss of CO2
from Europa’s atmosphere may have led to freezing oceans. Alkaline brine bubbles embed-
ded in ice in freezing and impact-thawing oceans could have provided a suitable environ-
ment for protocell formation and the large number of trials needed for biogenesis. Under-
standing these processes could be central to assessing the probability of life on Europa. Key
Words: Biogenesis—Ocean chemistry—Soda ocean—Alkalinity—Europa—Lake Van. Astro-
biology 2, 123–130.
123
INTRODUCTION
BIOG ENESIS is one of the most puzzling scien-
tific problems. Given life’s biochemical com-
plexity, it is a wonder it ever arose. Even if
Panspermia (Hoyle and Wickramasinghe, 1997)
is accepted as a way to propagate life, it does not
solve the fundamental problem of biogenesis but
shifts it from the Solar System to other places in
the galaxy. Searching for life or its biogeochemi-
cal signatures on Europa (e.g., Phillips and
Chyba, 2001) challenges our understanding of
biogenesis in general and may lead to an im-
proved understanding of biogenesis on Earth. Re-
cent discoveries about Europa suggest that evi-
dence of events that occurred in the early phases
of the Moon’s history may still exist. Europa most
probably hides a sizeable ocean below its ice crust
(e.g., Anderson et al., 1998; Greeley et al., 1998;
Pappalardo et al., 1999; Kargel et al., 2000); hy-
drated sodium carbonates, among other salts,
have been detected on Europa (McCord et al.,
1998, 1999); and it has been calculated that a net
loss of sodium occurs from Europa’s surface
(Johnson, 2000). These discoveries, which suggest
the existence of a hypocryotic, alkaline ocean,
could be central to assessing the probability of life
on Europa. Furthermore they are consistent with
1Institute of Applied Geosciences, University of Technology Darmstadt, Darmstadt, Germany.
2Polish Academy of Science, Institute of Paleobiology, Warszawa, Poland.
our hypothesis that early planetary alkaline
oceans favor biogenesis.
PRECONDITIONS FOR BIOGENESIS
Geochemical evidence such as the
d13C signa-
tures of rocks (e.g., Schidlowski et al., 1979; Mo-
jzsis
et al., 1996) suggests that photosynthesis and
therefore life were present on Earth at least 3.8
billion years ago. To understand biogenesis then,
we need to discuss the conditions of early oceans
in the frame of early planetary evolution.
Life most plausibly arose in an aqueous solution.
Oxygen and hydrogen are available throughout the
universe, and water is known to occur on several
planets and moons in the Solar System. Though the
possibility that life arose in small, ephemeral sys-
tems, such as lagoons or lakes, has recently been
discussed (e.g., Zavarzin, 1993; Zavarzin and
Zhilina, 2000), we propose that life arose in the
largest water bodies available (i.e., planetary
oceans), since it will take numerous trials until an
abiogenic phospholipid double-membrane vesicle
happens to contains just the right amounts of RNA,
ATP, and proteins to start basic life functions.
Such oceans should have had a composition
that favored the accumulation of organic matter.
An acidic composition would cause the hydroly-
sis of proteins and therefore hinder the preserva-
tion and accumulation of dissolved organic
macromolecules. An oxic composition is not plau-
sible either because it would oxidize organic mat-
ter much too quickly for biogenesis. With regard
to the origin of life, even an oceanic composition
close to that of Earth’s present oceans would not
be suitable since it would contain too high of a
Ca21concentration (,20 mEq/L) for proteins to
function. An ocean with a high Ca21concentra-
tion would also reduce the phosphate concentra-
tion by precipitating apatite, a problematic situ-
ation since high phosphate concentrations are
needed to form ATP, which fuels cellular reac-
tions. Recent life relies on highly sophisticated
proteins located in the cell membranes, the so-
called Ca-pumps, which continuously remove
Ca21from the protoplasm of the cell and keep
calcium concentrations at levels
,1026M (Orre-
nius et al., 1989; Trump and Berezesky, 1995).
Since these pumps most likely did not arise
ab ini-
tio (cf. Berridge, 1993; Berridge
et al., 1998), envi-
ronments that allow for a very low Ca21concen-
tration are arguably a promising site for
biogenesis (Kempe and Kazmierczak, 1994).
What might these environments have looked
like? The surfaces of some of the smaller planets
and those of the moons in our Solar System in-
dicate that impacting by asteroids and comets is
the main force behind planetary resurfacing
processes (e.g., Greeley and Batson, 1997). In the
case of the inner planets and the Moon, these im-
pacts produced widespread and thick silicate
rock ejecta blankets characterized by a wide ar-
ray of grain sizes. On Earth, these Archean ejecta
rocks contained fragments of komatiite rock, the
volcanic equivalent of mantle peridotites (e.g.,
Ringwood, 1975).
Degassing of the mantle and the arrival of wa-
ter by cometary impacts would have led to the im-
mediate onset of weathering of ejecta material. To
assess the composition of the resulting solutions,
it is important to understand the mass balance of
the inorganic weathering acids. Earth is the only
planet for which we can assess the total amounts
of the three main weathering acids—H2CO3, HCl,
and H2SO4—involved in weathering. It can be
shown that roughly 65.5 31021 g of C (equivalent
to 5.5 3102 1 mol of H2CO3), 52 31021g of Cl
(equivalent to 1.6 31021 mol of HCl), and 5.2 3
1021g of S (equivalent to 0.16 31021 mol of H2SO4)
have been consumed throughout Earth history
(Kempe and Degens, 1985). Restated, these calcu-
lations indicate that 3.7 times more carbonic acid
than hydrochloric acid and 34 times more car-
bonic acid than sulfuric acid have been available
for surficial weathering reactions. However, since
the primordial komatiitic crust had a [Ca211
Mg21]/[Na11K1] of 1.6, it is apparent that not
enough chloride and sulfate was available to bal-
ance Na1and K1, and some of the Na1and K1
must have been balanced by carbonate ions. As
the bulk chemistry of extrusive igneous rocks
changed throughout Earth history and significant
proportions of basaltic rocks with lower Mg con-
centrations succeeded komatiites, Na- and K-car-
bonates would have been favored. Therefore
weathering solutions on early Earth, like those of
the present, must have had a predominance of car-
bonate ions and not of chloride ions.
Garrels and Mackenzie (1967) have shown what
happens if solutions of various compositions are
subjected to evaporation. As long as there is a small
surplus of carbonates over Ca211Mg21and a sur-
plus of Na11K1over Cl21SO422, evaporating
solutions will quickly become alkaline. This is be-
cause concentration by evaporation will force Ca-
and Mg-salts to precipitate first owing to their
lower solubility product compared with Na- and
KEMPE AND KAZMIERCZAK
124
K-salts. As the overall concentration in the solu-
tion increases, so does the alkalinity (the charge
sum of the weak acids in solution, largely
HCO3212 CO322). This will cause the pH to rise
in spite of the fact that sodium, potassium, chlo-
ride, and sulfate may also be present in the solu-
tion in appreciable amounts. The excess of Na1
and demand of H1in such solutions would ap-
pear to hinder proton-coupled cell energetics. It
has been demonstrated, however, that Na1(the
Na-cycle) may replace H1as a parallel energy-
transducing mechanism (e.g., Skulachev, 1984).
A WEATHERING EXPERIMENT
The results of a dissolution experiment in
which pulverized komatiite was exposed only to
ambient pCO2are shown in Fig. 1. Within ,10
days, equilibrium was reached in a solution rich
in Mg21, with Ca21and Na1found in lower con-
centrations and K1and Fe21occurring in only
minor amounts. The main anion at equilibrium
was bicarbonate (HCO32), which suggests that
upon evaporation Na- and K-carbonates would
precipitate, making the solution progressively
more alkaline. The result of our experiment is
similar to that obtained by MacLeod
et al. (1994)
using basalt and komatiite in reactions with stan-
dard seawater at different temperatures. In both
types of experiments the resulting fluids were in-
variably alkaline.
LAKE VAN, TURKEY—AN EXAMPLE OF
A MODERN ALKALINE LAKE
Though it is difficult to assess theoretically
whether alkaline conditions characterized the early
terrestrial ocean (cf. also Morse and Mackenzie,
ALKALINE OCEAN HYPOTHESIS 125
FIG. 1. Dissolution experiment with a 2.7–billion-year-old komatiite of the Abitibi Greenstone Belt, talus of Pike
Hill, Munro Township, Canada, provided by Dr. David Williams, Arizona State University. Distilled water (500
ml) was added to pulverized unweathered komatiite (653 mg), and the mixture was stirred continuously at standard
temperature (,18–22°C) and lab pCO2(,600 ppmv) for several weeks (x-axis). Subsamples of the solution were with-
drawn at the indicated intervals, filtered, and analyzed for major elements with flame-atomic absorption spec-
trophotometry. Concentrations (y-axis) stabilized after
,30 days. The principal anion is HCO32, obtained from CO2
of ambient air.
1998), such conditions exist today in modern soda
lakes (Fig. 2). These lakes occur almost exclusively
in volcanic regions characterized by a bulk chem-
istry of basaltic, andesitic, or even dacitic compo-
sition. Apparently weathering by hydrochloric or
hydrosulfuric acid plays only a small role while
Na- and K-balanced alkalinity is produced in large
quantities. The largest of these soda lakes is 450-m-
deep Lake Van in Turkey (Kempe, 1977) with an
alkalinity of 155 mEq/L and a pH of 9.87 (sample
from a depth of 200 m) (Kempe and Kazmierczak,
1994). Its total Ca21level is as low as 3.7 mg/L (93
mmol/L), but owing to high concentrations of
CO322, HCO32, Cl2, and SO422and the presence
of their ion pairs with Ca21, the free Ca21level is
much lower (i.e., ,20 mmol/L). This is only 20
times higher than cytosolic levels. Under presumed
Precambrian alkaline ocean conditions, Ca21levels
must have been even lower since alkaline condi-
tions sustain high SiO2concentrations, fostering
bonding of free calcium in silicates as well. In mod-
ern soda lakes, SiO2concentrations are governed
by diatoms; therefore one of the regulators for the
free Ca concentrations is missing compared with
presumed early ocean conditions. Even though Ca
concentrations are low in Lake Van, the high alka-
linity causes supersaturation of calcite and arago-
nite by a factor of 10. Supersaturation results in
widespread precipitation of aragonite in the water
column (whitings) and on the surfaces of cyanobac-
terial mats that form up to 40-m-high submerged
tufa towers (Kempe
et al., 1991) that rise above Ca-
rich groundwater seeps. These conditions are likely
to have prevailed throughout the Precambrian,
consistent with the widespread occurrence of stro-
matolites, limestones, and dolomites in the early
rock record.
CREATION AND LOSS OF THE
“SODA OCEAN” THROUGHOUT
EARTH HISTORY
This modern example of a soda lake and the
theoretical geochemical considerations discussed
provide insight into the workings of a primordial
alkaline ocean [nicknamed the “Soda Ocean”
(Kempe and Degens, 1985)].
Mass balance consideration of the amount of
dissolved silica discharged to the Earth’s oceans
KEMPE AND KAZMIERCZAK
126
FIG. 2. Locations of the principal alkaline lakes on Earth in relation to plate boundaries. Almost all of the alka-
line lakes are related to volcanic rocks, some occur along subduction zones, some are related to divergent plate bound-
aries, and some belong to hot spots. Highly alkaline sodium carbonate (soda) lakes occur in Africa, America, and
Asia. Lakes with lower alkalinity either have an outflow (i.e., Lake Taupo) or are relatively young (i.e., crater lake of
Niuafo’ou). Two crater lakes filled with seawater are alkaline because of sulfate reduction in the hypolimnion (i.e.,
Satonda, Kauhako). The Lake of Santorini existed only during the last Glacial and left impressive stromatolites, which
now occur as xenoliths in the pumice of the Minoean eruption. The authors led expeditions to Lake Van, Turkey
(1989, 1990), Satonda (1986, 1993), Niuafo’ou (1998), Kauhako (1999, 2000, 2001), and Santorini (1999).
can be used to calculate the rate at which silicate
minerals, preferentially alkali feldspars, are con-
sumed by carbonic acid weathering today,
amounting to roughly 0.1 billion tons of Cin organic/
year (Kempe, 1979). Compared with the total
oceanic content of HCO321CO322of 38,400 bil-
lion tons of Cinorganic (e.g., Falkowski
et al., 2000),
the present oceans recycle their inorganic carbon
by silicate weathering within 0.4 million years. In
fact, continental weathering alone binds a volume
of CO2equivalent to the present mass of CO2in
the atmosphere within only 7,000 years. It is un-
derstood that these mass balance calculations ap-
ply only to the inorganic carbon cycle and that
other processes like the biologically driven or-
ganic carbon cycle counterbalance these fluxes.
Nevertheless these examples show that silicate
weathering is a geologically rapid pathway to se-
quester free CO2from planetary atmospheres in
the absence of life. If ever Earth had a high pCO2,
as suggested by many astrophysicists and geolo-
gists to counterbalance the early faint sun effect
in their models (e.g., Holland, 1984; Kasting, 1987;
Caldeira and Kasting, 1992), it could not have per-
sisted for long in the presence of water. Alterna-
tively, if methane, a much more effective green-
house gas, was continuously produced by
reducing reactions in the ocean it could have kept
Earth from freezing.
If Earth had an alkaline early ocean, one must
question how it was lost. Our model suggests that
this was done by subducting seawater along with
marine sediments and oceanic crust (Kempe and
Degens, 1985). Since the rate of seawater sub-
duction is
,1 km3/year, the half-life of any com-
pound in the ocean is
,1 billion years. Given that
the rate of subduction throughout the Precam-
brian was more rapid than today, the half-life of
dissolved compounds in the ocean would have
been even shorter in the past. The growing con-
tinents (e.g., Godderis and Veizer, 2000) would
have consumed the marine Na1and K1to form
the alkali feldspars of the granodioritic continen-
tal crust, and the carbonates would be recycled
and eventually stored in limestones and
dolomites (bound to Ca21and Mg21derived
from further weathering of olivine and plagio-
clases of the komatiites) or as organic carbon on
the continents. Thus carbon, which existed in the
primordial ocean almost entirely in ionic form,
would have been redistributed into the compart-
ments of the Earth’s system where we find it to-
day. The gradual reduction in ocean alkalinity
would have given life time to adapt to the pres-
ent quite toxic ocean chemistry.
Figure 3 illustrates how the terrestrial ocean
chemistry could have changed through time, sug-
gesting that an alkaline ocean would no longer
exist by the end of the Precambrian. The increas-
ing Ca21concentration of the ocean could have
triggered such important evolutionary innova-
tions as increased cell size, protection of the DNA
in a separate membrane (i.e., the evolution of the
eukaryotic cell), and the onset of multicellularity
(Kempe and Kazmierczak, 1994). These evolu-
tionary changes may reflect adaptations to the ris-
ing Ca21concentration of the oceans. Ocean
chemistry changed even more when the rising O2
concentration in the atmosphere made the pres-
ence of sulfate possible. This situation, accompa-
nied by the dissolution of gypsum, allowed the
Ca21concentration to increase beyond any pre-
vious level, and cells may have adapted and
evolved because of these environmental pres-
sures. Two existing biochemical strategies could
explain how life adapted to such conditions. Mi-
croorganisms may have evolved to excrete large
amounts of Ca-binding extracellular polymer
substances (i.e., where Ca21is bound to amino
acids such as aspartic and glutamic acid), or they
may have evolved to precipitate Ca21in a con-
trolled manner enzymatically inside or outside of
the cell [i.e., they would precipitate biominerals
(Lowenstam and Margulis, 1980; Kempe and
Kazmierczak, 1994)].
IMPLICATIONS FOR BIOGENESIS IN
EUROPA’S OCEAN
According to our model, planets that did not
develop plate tectonics would remain in the soda
ocean phase forever. Life on these planets, even
though present, would not have had the geo-
chemical forcing to evolve into multicellular or-
ganisms. If Mars had oceans, they should have
been alkaline as well (Kempe and Kazmierczak,
1997). Martian lake sediments should therefore
contain Ca- and Mg-carbonates and widespread
cherts, which in evaporative settings should con-
tain, in addition to halite, sodium carbonate salts.
An alkaline ocean could have arisen on Europa
as well. Comets bringing CO2and H2O would
have repeatedly impacted the underlying silicate
crust, thus producing weathering solutions of
high carbonate concentration. Consecutive comet
ALKALINE OCEAN HYPOTHESIS 127
impacts could have thawed and evaporated Eu-
ropa’s ocean several times, thereby precipitating
the solutes. As the water and CO2-rich atmo-
sphere cooled after impacts, weathering would
have resumed and added more salts to the ocean.
The repeated impact-generated evaporation and
consecutive condensation would have favored
the development of an alkaline ocean early in Eu-
ropa’s history. This scenario is not constrained by
the composition of the silicate rocks, as long as
the amount of CO2available is larger than the
amount of Ca and Mg liberated during weather-
ing. If life emerged in such an environment as
rapidly as it did on Earth, it could have estab-
lished itself on Europa before the lack of subse-
quent impacts and total consumption of CO2
from the primordial atmosphere caused the moon
to freeze over permanently.
McCord et al. (1998, 1999) interpreted the
Galileo near-infrared mapping spectrometer
spectra recorded from Europa’s darker regions to
be caused by the presence of hydrated sodium
carbonates and magnesium sulfates. Johnson
(2000) used the data to calculate fluxes of sodium
to and from Europa and determined that Europa
is a net source of sodium (i.e., a flux of
,2–4 3106
Na molecules/cm2/s leaves the surface whereas a
flux of
,0.2–0.8 3106Na molecules/cm2/s, which
originates from Io, is implanted on the surface).
Johnson (2000) also calculated that the surface con-
centration of sodium could amount to as much as
0.5 wt% of the surface. Kargel
et al. (2000) discuss
various options for an ocean composition on Eu-
ropa, including among them a sodium carbonate
ocean. If a sulfuric acid ocean exists on Europa (e.g.,
Kargel
et al., 2000), then it is unlikely that life ever
evolved in its ocean since proteins would be hy-
drolyzed and the high concentrations of Mg21and
Ca21would denature proteins, inhibiting their
proper biochemical functioning. However, accord-
ing to our hypothesis, the presence of an alkaline
ocean could support biogenesis.
IMPLICATIONS FOR BIOGENESIS IN A
FREEZING OCEAN
Freezing and thawing of alkaline solutions
could provide a suitable environment for proto-
cell formation by trapping solution pockets
KEMPE AND KAZMIERCZAK
128
FIG. 3. A geochemical scenario illustrating the “Soda Ocean” hypothesis as the ocean evolved throughout Earth
history (x-axis) (altered after Kempe and Kazmierczak, 1994). After the initial equilibration of water and CO2with
volcanic silicates through weathering (Urey reaction), the ocean would have had a high carbonate alkalinity (left-
hand scale) and a moderately high pH (right-hand side). Consequently, the total calcium concentration would have
been low while the CaCO3supersaturation [top of graph with separate scale for calcite (Cc) supersaturation index]
would have been very high (i.e.,
.0.8), above which spontaneous inorganic precipitation regulates Ca concentration.
Because of the slow decrease of alkalinity in the ocean through subduction of seawater, the Soda Ocean would have
lasted through much of geological history. The “Halite Ocean” would have prevailed for only the last 1 billion years.
In the Phanerozoic sulfate reduction could have modulated ocean alkalinity, either globally or in isolated basins, ow-
ing to the development of anoxia in bottom waters [i.e., owing to the “alkalinity pump” (Kempe and Kazmierczak,
1994)]. The Cc saturation was then governed by biomineralization, which today keeps seawater at supersaturation
lower than required for inorganic precipitation.
within the ice and slowly squeezing the compo-
nents to ever higher concentrations. Shrinking
residual brine bubbles could have provided the
large number of trials needed for biogenesis. The
potential for nonenzymatic nucleic acid synthesis
in freezing aqueous solutions was recently re-
ported by Kanavarioti et al. (2001). Under such
conditions, it is possible that at least one or more
vesicles could contain the right selection of pro-
teins, phospholipids, ATP, and RNA strands and
start life. Thus the lack of a warming CO2at-
mosphere may even prove advantageous to the
formation of life. Even on Earth the ocean could
have gone through several phases of freezing and
thawing in the time period of the terminal cata-
clysm (Sleep and Zahnle, 2001; Sleep
et al., 2001).
Such a model for biogenesis would explain why
life evolved so quickly on Earth, its formation the
consequence of the physical and geochemical set-
ting in the first 0.5 billion years of its history. Sim-
ilarly, if our hypothesis of a soda ocean on Eu-
ropa should prove true, then the biogeochemical
window for life to emerge in its ocean could have
appeared relatively rapidly.
ACKNOWLEDGMENTS
This paper was written as a follow-up of a talk
invited by Ron Greeley and given at the Europa
Focus Group Workshop at the NASA Ames Re-
search Center, February 1–2, 2001. The paper
greatly improved through comments by J.E. Kle-
maszewski, R. Greeley, and an unnamed re-
viewer. Field work on terrestrial soda lakes was
supported by the Deutsche Forschungsgemein-
schaft, the Polish Academy of Sciences, and the
Foundation for Polish Science.
REFERENCES
Anderson, J.D., Schubert, G., Jacobson, R.A., Lau, E.L.,
Moore, W.B., and Sjogren, W.L. (1998) Europa’s differ-
entiated internal structure: inferences from four Galileo
encounters.
Science 281, 2019–2022.
Berridge, M.J. (1993) Inositol trisphosphate and calcium
signalling. Nature 361, 315–325.
Berridge, M.J., Bootman, M.D., and Lipp, P. (1998) Cal-
cium—a life and death signal.
Nature 395, 645–648.
Caldeira, K. and Kasting, J.F. (1992) Susceptibility of the
early Earth to irreversible glaciation caused by carbon
dioxide clouds.
Nature 359, 226–228.
Falkowski, P., Scholes, R.J., Boyle, E., Canadell, J., Can-
field, J., Elser, J., Gruber, N., Hibbard, K., Hogberg, P.,
Linder, S., Mackenzie, F.T., Moore, B. III, Pedersen, T.,
Rosenthal, Y., Seitzinger, S., Smetacek, V., and Steffen,
W. (2000) The global carbon cycle: a test of our knowl-
edge of Earth as a system.
Science 290, 291–296.
Garrels, R.M. and Mackenzie, F.T. (1967) Origin of the
chemical composition of some springs and lakes. In
Ad-
vances in Chemistry, Vol. 67: Equilibrium Concepts of Nat-
ural Water Systems, American Chemical Society, Wash-
ington, DC, pp. 222–242.
Godderis, Y. and Veizer, J. (2000) Tectonic control of
chemical and isotopic composition of ancient oceans:
the impact of continental growth. Am. J. Sci. 300,
434–461.
Greeley, R. and Batson, R. (1997)
The NASA Atlas of the
Solar System, Cambridge University Press, Cambridge.
Greeley, R., Sullivan, R., Klemaszewski, J., Homan, K.,
Head, J.W. III, Pappalardo, R.T., Veverka, J., Clark, B.E.,
Johnson, T.V., Klaasen, K.P., Belton, M., Moore, J., As-
phaug, E., Carr, M.H., Neukum, G., Denk, T., Chap-
man, C.R., Pilcher, C.B., Geissler, P.E., Greenberg, R.,
and Tufts, R. (1998) Europa: initial Galileo geological
observations.
Icarus 135, 4–24.
Holland, H.D. (1984)
The Chemical Evolution of the Atmo-
sphere and Oceans, Princeton University Press, Prince-
ton, NJ.
Hoyle, F. and Wickramasinghe, C. (1997)
Life on Mars? The
Case for a Cosmic Heritage?, Clinical Press, Bristol.
Johnson, R.E. (2000) Sodium at Europa. Icarus 143,
429–433.
Kanavarioti, A., Monnard, P.-A., and Deamer, D.W. (2001)
Eutectic phases in ice facilitate nonenzymatic nucleic
acid synthesis. Astrobiology 1, 271–281.
Kargel, J.S., Kaye, J.Z., Head, J.W. III, Marion, G.M.,
Sassen, R., Crowley, J.K., Prieto, O., Grant, S., and
Hogenboom, D.L. (2000) Europas’s crust and ocean: ori-
gin, composition, and the prospects for life.
Icarus 148,
226–265.
Kasting, J.F. (1987) Theoretical constraints on oxygen and
carbon dioxide concentrations in the Precambrian at-
mosphere.
Precambrian Res. 34, 205–229.
Kempe, S. (1977) Hydrographie, Warvenchronologie und
organische Geochemie des Van Sees, Osttürkei [Dis-
sertation]. Mitteilungen des Geologisch-Paläontolgischen
Institutes der Universität Hamburg 47, 125–228.
Kempe, S. (1979) Carbon in the freshwater cycle. In
SCOPE Report 13: The Global Carbon Cycle, edited by B.
Bolin, E.T. Degens, S. Kempe, and P. Ketner, John Wi-
ley & Sons, Chichester, pp. 317–342.
Kempe, S. and Degens, E.T. (1985) An early soda ocean?
Chem. Geol. 53, 95–108.
Kempe, S. and Kazmierczak, J. (1994) The role of alkalin-
ity in the evolution of ocean chemistry, organization of
living systems and biocalcification processes. In
Bulletin
of the Institute of Oceanography, Special No. 13: Past and
Present Biomineralization Processes. Considerations About
the Carbonate Cycle, edited by F. Doumenge, Institute of
Oceanography, Monaco, pp. 61–117.
Kempe, S. and Kazmierczak, J. (1997) A terrestrial model
for an alkaline martian hydrosphere. Planet. Space Sci.
45, 1493–1499.
Kempe, S., Kazmierczak, J., Landmann, G., Konuk, T.,
ALKALINE OCEAN HYPOTHESIS 129
Reimer, A., and Lipp, A. (1991) Largest known micro-
bialites discovered in Lake Van, Turkey. Nature 349,
605–608.
Lowenstam, H. and Margulis, L. (1980) Evolutionary pre-
requisites for early Phanerozoic calcareous skeletons.
BioSystems 12, 27–41.
MacLeod, G., McKeown, C., Hall, A.J., and Russell, M.J.
(1994) Hydrothermal and oceanic pH conditions of pos-
sible relevance to the origin of life.
Orig. Life Evol. Biosph.
24, 19–41.
McCord, T.B., Hansen, G.B., Fanale, F.P., Carlson, R.W.,
Matson, D.L., Johnson, T.V., Smythe, W.D., Crowley,
J.K., Martin, P.D., Ocampo, A., Hibbitts, C.A., and
Granahan, J.C. (1998) Salts on Europa’s surface detected
by Galileo’s near infrared mapping spectrometer. The
NIMS Team.
Science 280, 1242–1245.
McCord, T.B., Hansen, G.B., Matson, D.L., Johnson, T.V.,
Crowley, J.K., Fanale, F.P., Carlson, R.W., Smythe,
W.D., Martin, P.D., Hibbitts, C.A., Granahan, J.C., and
Ocampo, A. (1999) Hydrated salt minerals on Europa’s
surface from the Galileo near-infrared mapping spec-
trometer (NIMS) investigation. J. Geophys. Res. Planets
104, 11827–11851.
Mojzsis, S.J., Arrhenius, G., McKeegan, K.D., Harrison,
T.M., Nutman, A.P., and Friend, C.R.L. (1996) Evidence
for life on Earth before 3,800 million years ago.
Nature
384, 55–59.
Morse, J.W. and Mackenzie, F.T. (1998) Hadean ocean car-
bonate geochemistry. Aquatic Geochem. 4, 301–319.
Orrenius, S., McConkey, D.J., Beilomo, G., and Nicotera,
P. (1989) Role of CA21in toxic cell killing.
Trends Phar-
macol. Sci. 10, 281–285.
Pappalardo, R.T., Belton, M.J.S., Breneman, H.H., Carr,
M.H., Chapman, C.R., Collins, G.C., Denk, T., Fagents,
S., Geissler, P.E., Giese, B., Greeley, R., Greenberg, R.,
Head, J.W., Helfenstein, P., Hoppa, G., Kadel, S.D.,
Klaasen, K.P., Klemaszewski, J.E., Magee, K., McEwen,
A.S., Moore, J.M., Moore, W.B., Neukum, G., Phillips,
C.B., Prockter, L.M., Schubert, G., Senske, D.A., Sulli-
van, R.J., Tufts, B.R., Turtle, E.P., Wagner, R., and
Williams, K.K. (1999) Does Europa have a subsurface
ocean? Evaluation of the geological evidence. J. Geo-
phys. Res. Planets 104, 24015–24055.
Phillips, C.B. and Chyba, C.F. (2001) Europa: prospects
for an ocean and life. In
First Steps in the Origin of Life
in the Universe; Proceedings of the 6th Trieste Conference
on Chemical Evolution, edited by J. Chela-Flores, T.
Owen, and F. Raulin, Kluwer, Dordrecht, in press.
Ringwood, A.E. (1975) Composition and Petrology of the
Earth’s Mantle, McGraw-Hill, New York.
Schidlowski, M., Appel, P.W., Eichmann, R., and Junge,
C.E. (1979) Carbon isotope geochemistry of the 3.7 3
109yr old Isua sediments, West Greenland: implications
for the Archean carbon and oxygen cycles. Geochim.
Cosmochim. Acta 43, 189–199.
Skulachev, V.P. (1984) Sodium bioenergetics. Trends
Biochem. Sci. 9, 483–485.
Sleep, N.H. and Zahnle, K. (2001) Carbon dioxide cycling
and implications for climate on ancient Earth. J. Geo-
phys. Res. Planets 106, 1373–1399.
Sleep, N.H., Zahnle, K., and Neuhoff, P.S. (2001) Initia-
tion of clement surface conditions on the earliest Earth.
Proc. Natl. Acad. Sci. USA 98, 3666–3672.
Trump, B.F. and Berezesky, I.K. (1995) Calcium-mediated
cell injury and cell death.
FASEB J. 9, 219–228.
Zavarzin, G.A. (1993) Epicontinental soda lakes as prob-
able relict biotopes of terrestrial biota formation. Mi-
crobiology 62, 474–479.
Zavarzin, G.A. and Zhilina, T.N. (2000) Anaerobic
chemotrophic alkaliphiles. In
Journey to Diverse Micro-
bial Worlds, edited by J. Seckbach, Kluwer, Amsterdam,
pp. 191–208.
Address reprint requests to:
Dr. Stephan Kempe
Institute of Applied Geosciences
University of Technology Darmstadt
Schnittspahnstrasse 9
D-64287 Darmstadt, Germany
E-mail: kempe@geo.tu-darmstadt.de
KEMPE AND KAZMIERCZAK
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