Gutiérrez‑Ariza et al.
Progress in Earth and Planetary Science(2024) 11:11
https://doi.org/10.1186/s40645-023-00603-w

RESEARCH ARTICLE

Progress in Earth andPlanetary Science

Open Access

Magnesium silicate chimneys at the Strytanhydrothermal field, Iceland, as analogues
for prebiotic chemistry at alkaline submarinehydrothermal vents on the early Earth
Carlos Gutiérrez‑Ariza1, Laura M. Barge2, Yang Ding3, Silvana S. S. Cardoso3, Shawn Erin McGlynn4,5,
Ryuhei Nakamura4,5, Donato Giovanelli4,6, Roy Price7, Hye Eun Lee4, F. Javier Huertas1,
C. Ignacio Sainz‑Díaz1 and Julyan H. E. Cartwright1,8*   

Abstract
The Strytan Hydrothermal Field (SHF) in basaltic terrain in Iceland is one of the extant alkaline submarine hydrother‑mal vent systems favoured as analogues for where life on Earth may have begun. To test this hypothesis we analyse
the composition, structure, and mineralogy of samples from hydrothermal chimneys generated at the SHF. We findthat the chimney precipitates are composed of Mg-silicates including clays of the saponite-stevensite group (highMg and Si, low Fe and Al), Ca-carbonates and Ca-sulfates. The chimneys comprise permeable structures with pores
sizes down to 1 µm or less. Their complex interiors as observed with SEM (Scanning Electron Microscopy) and X-ray
CT (computed tomography scanning), exhibit high internal surface areas. EDX (energy-dispersive X-ray spectroscopy)
analysis reveals an increase in the Mg/Si ratio toward the chimney exteriors. Chemical garden analogue experiments
produce similar Mg–silicate chimneys with porous internal structures, indicating that injection-precipitation experi‑ments can be high-fidelity analogues for natural hydrothermal chimneys at the SHF. We conclude that SHF chimneys
could have facilitated prebiotic reactions comparable to those proposed for clays and silica gels at putative Hadean
to Eoarchean alkaline vents. Analysis of the fluid dynamics shows that these chimneys are intermediate in growth ratecompared to faster black smokers though slower than those at Lost City. The SHF is proposed as a prebiotic alkaline
vent analogue for basaltic terrains on the early Earth.
Keywords Alkaline submarine hydrothermal vents, Strytan hydrothermal field, Prebiotic chemistry, Origin of life
*Correspondence:
Julyan H. E. Cartwrightjulyan.cartwright@csic.es
1
Instituto Andaluz de Ciencias de la Tierra, CSIC–UGR​, 18100 Armilla,
Granada, Spain
2
NASA Jet Propulsion Laboratory, California Institute of Technology,
Pasadena, CA, USA
3
Department of Chemical Engineering and Biotechnology, Cambridge
University, Cambridge CB3 0AS, UK
4
Earth‑Life Science Institute, Tokyo Institute of Technology, 2‑12‑1
Ookayama, Meguro‑ku, Tokyo 152‑8550, Japan
5
Center for Sustainable Resource Science, RIKEN, 2‑1 Hirosawa, Wako,
Saitama 351‑0198, Japan
6
Department of Biology, University of Naples “Federico II”, MonteSant’Angelo, Edificio 7, Stanza 1D‑22, 80126 Naples, Italy

7
School of Marine and Atmospheric Sciences, Stony Brook University,
Stony Brook, NY 11794‑5000, USA
8
Instituto Carlos I de Física Teórica y Computacional, Universidad deGranada, 18071 Granada, Spain© The Author(s) 2024. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which
permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to theoriginal author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images orother third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line
to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory
regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of thislicence, visit http://​creat​iveco​mmons.​org/​licen​ses/​by/4.​0/.

Gutiérrez‑Ariza et al. Progress in Earth and Planetary Science(2024) 11:11

1 Introduction
Across the ocean floor one finds hydrothermal vents
emitting mineral-laden waters of higher temperatureand different pH and composition than ambient seawater. Owing to the differences in concentration, pH,
and temperature, minerals are deposited at these vents,
where solid chimney structures are formed that reachmany metres in height. The composition and timescale of hydrothermal chimney formation varies greatly
between different types of vents, whose geochemical
characteristics are a result of the host rock type and thedegree of magmatic input. On Earth today, vents range
from acidic, ~ 300–400 °C “black smokers” with metalsulfide rich chimneys; intermediate temperature (around
100–300 °C) acidic “white smokers” (Gamo et al. 2004;
Kormas et al. 2006; Fustec et al. 1987); and lower-temperature (less than 100 °C) vents with chimneys of brucite and carbonates formed via serpentinization that can
range from seawater pH to very alkaline (Okumura et al.
2016a, b; Kelley et al. 2005; Ludwig et al. 2006; Lecoeuvre
et al. 2021; Monnin et al. 2014; 2021). These serpentinization-hosted vents generate hydrogen from hydrationof olivine, providing energy to support microbial life
(Proskurowski et al. 2008; Kelley et al. 2005).
The Lost City Hydrothermal Field (LCHF) in thenorth Atlantic Ocean was the first discovered serpentinite-hosted deep-sea vent, and its properties haveformed the basis for a detailed emergence-of-life theory (Russell and Hall 1997, 2006; Martin et al. 2008)
based on the LCHF redox, pH, and chemical gradientsthat mimic the gradients that life harnesses across cellular membranes (Lane and Martin 2012). It has been
proposed that in an early Earth context, a LCHF-likehydrothermal chimney composed of Fe(II)-bearinghydroxides/sulfides/carbonates (due to the anoxic,­Fe2+-rich early oceans; MacLeod et al. 1994; Jiang andTosca 2019; Tosca et al. 2016; Halevy et al. 2017) could
have driven prebiotic reactions such as C
­ O2 reduction
and amino acid synthesis toward the emergence of life
(Russell and Hall 2006; Russell 2018). The first precipitate in LCHF chimneys is brucite, Mg(OH)2, whenalkaline vent fluids react with M­ g2+ in seawater. Simul2+
taneously, dissolved C­ a in vent fluids can mix with
­HCO3− in seawater to precipitate calcium carbonate(Früh-Green et al. 2003); in an early Earth ocean thefirst precipitate at a similar vent would therefore be
ferrobrucite and/or green rust (Russell 2018). Green
rust—a double layered Fe(II)/Fe(III)-hydroxide—is amineral of great interest in environmental science andwastewater treatment due to its versatile adsorption
capacity and reactivity; e.g., it absorbs phosphorus, anddrives abiotic nitrogen redox cycling through reductionof nitrate/nitrite (Hansen et al 2001; Barthélémy et al.

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2012; Etique et al. 2014). The presence of green rustin prebiotic alkaline vent chimneys is central to thisorigin-of-life theory; since green rust is proposed tofunction as a “nano-engine” driving synthesis of aminoacids/peptides/proto-enzymes capable of harnessinghydrothermal pH and redox gradients toward the emergence of autotrophic metabolism (Russell 2018, 2023).
However, it is still unclear what the properties of early
Earth seafloor and ocean crust were and thus what thegeochemical characteristics of alkaline vents would
have been; i.e., whether they would have been LCHFlike—resulting from aqueous alteration of olivine-richcrust—or whether they would have been more similar
to basalt-hosted vents (Miyazaki and Korenaga 2022;
Barnes and Arndt 2019; Papineau et al. 2022) or evenvents produced by aqueous alteration of komatiite (Ueda
et al. 2021). The Strytan Hydrothermal Field (SHF), Eyjafjord, Iceland, is the only known alkaline basalt-hostedhydrothermal vent (Price et al. 2017; Barge and Price
2022, Rucker et al. 2023), and thus represents a crucial
analogue for early Earth alkaline hydrothermal systems
that could be amenable for origin-of-life processes (Russell and Hall 1997; Russell 2018, 2023). The SHF emits
alkaline (pH ~ 10.2), hot (~ 70 °C) freshwater hydrothermal fluids, that are enriched in dissolved ­SiO2 and results
in precipitation of Mg–silicate (saponite) chimneys up to
55 m tall (Barge and Price 2022; Price et al. 2017; Geptner
et al. 2002; Stanulla et al. 2017; Marteinsson et al. 2001).
The SHF chimneys host similar pH, redox, and temperature gradients to the LCHF chimneys (Lane & Martin 2012), and in addition, SHF chimneys exhibit a ­Na+
gradient between the vent fluid (sourced from meteoric
water) and seawater (Price et al. 2017). Previous studies
have focused on the microbiology (Marteinsson et al.
2001; Twing et al. 2022) and chimney mineralogy/structure (Stanulla et al. 2017; Geptner et al. 2002) of the SHF;
however, the composition of the SHF chimneys has notbeen characterized in a prebiotic context: i.e., whether
the important reactions proposed in a LCHF context
would also be likely to occur in a SHF-like early-Earthsystem.
In the present work we examine material collectedfrom SHF chimneys. We present a structural and compositional overview of two samples of SHF chimneys withscanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray computed tomography (XCT).
We compare the vent material with laboratory produced
analogue structures from experiments of the type thathave been previously used to simulate hydrothermal
chimneys (Barge et al. 2019; Hermis et al. 2019). Our goal
is to understand whether the SHF chimneys exhibit compositions and mineralogy consistent with reactants andGutiérrez‑Ariza et al. Progress in Earth and Planetary Science(2024) 11:11

catalysts necessary to drive prebiotic reactions in an early
Earth context.
1.1 The Strytan hydrothermal vent system

An intense hydrothermal activity is observed in many
localities in Iceland, due to its location on the MidAtlantic Ridge (MAR) and as a mantle hotspot (Celli
et al. 2021). Although the common subaerial features
are gas emissions, hot springs and mud volcanoes, submarine hydrothermal activity occurs as well. Strytanhydrothermal vents are located in Eyjafjordur, north of
Akureyri, 1.8 km offshore in the northeastern part of thefjord. The bedrocks are Tertiary basaltic lavas, 6–12 My
old (Bjornsson 1981). Geothermal activity is connectedwith tectonic features dominating the area, in particular
the intersection of NW fault zone and the predominant
NNE tectonic trend. However, there are no magmatic
inputs, and the only contribution to the hydrothermal
system from the MAR is heat. The geothermal field consists of a series of steep cones rising from the seafloor atapproximately 70–80 m below sea level. They are aligned
along faults, generally trending E–W (Marteinsson et al.
2001). The largest cone reaches approximately 15 m bsl,
and is around 55 m in total height. The cones consist
predominantly of saponite precipitates, but also containsediments and shells embedded in the material (Geptner
et al. 2002).
The hydrothermal fluids are composed of meteoric rainwaters—and are thus fresh—falling on the high groundinland to the south (Marteinsson et al. 2001), that percolate deep into the bedrock and flow tens of km before
ascending to the surface through the tectonic features
while they draw heat from surrounding rocks. The discharged hydrothermal fluids at Strytan show maximum
measured temperature in the active discharge points
of approximately 70 °C, high pH values up to 10.2, andhigh silica content of ~ 94 mg L
­ −1 out of a total mineral−1
concentration of 291 mg ­L , (i.e., ~ 1/3 silica) (Marteinsson et al. 2001). Images of the vents where samples weretaken for this study are given in Fig. 1A, B.

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Two field samples (S1 and S2) collected from the
Strytan vents (Fig. 1C, D) were studied. In sample S1
there were identified two zones, termed S1(tube), owing
to the existence of some parallel tubes, and S1(tip)(Fig. 1E). Specific zones of these samples with particular
microstructures were investigated: Two zones in sample
S2, S2(top), and S2(bottom), were investigated for theirdifferent colours (Fig. 1F). These zones were extracted
from the whole sample, and portions of these were studied separately. One portion was ground in an agate mortar and analysed by powder X-ray diffraction (XRD).
Scanning electron microscopy (SEM) was performed
using FEI Quanta 400 and 650 microscopes. Chemical analysis of the micromorphology was determinedby EDX analysis. Transmission and analytical electron microscopy (TEM-AEM) was performed in a FEITITAN G2 microscope, with an XFEG emission gun, aspherical aberration corrector, and a high-angle annulardark-field (HAADF) detector. Samples were ground inan agate mortar, suspended in pure ethanol and dropped
on Cu grids. Analyses were performed at 300 kV with aresolution of ~ 0.2 nm in the high-resolution (HRTEM)
mode and ~ 2 nm in scanning TEM (STEM) mode
(where the STEM method uses an HAADF detector).
Compositional analysis was performed with a Super X
micro X-ray analyser equipped with four detectors by
EDX. In addition, ultrathin sections were prepared withsamples encased in resin. X-ray computed tomography(XCT) was performed in an Xradia 510 VERSA tomograph. A 0.4X detector was used. Given that the two
samples present a noticeable difference in density, theoperating parameters vary from one to another. For S1
we set 80 kV potential, 87 µA current, and a 7 W target
power; exposure time was 2 s and pixel size 17.1 µm. For
S2, the configuration was set instead to 50 kV potential,
80 µA current, and 3.98 W target power; exposure timewas 15 s and pixel size was 12.22 µm. Data processing
was performed using Scout and Scan Control System
12.0.8059 and Reconstructor Scout and Scan 12.0.8059.
Further data treatment and visualization were carriedout with the FIJI distribution of ImageJ including the
3DViewer plugin.

2 Methods
2.1 Field sample analysis

2.2 Laboratory chemical garden experiments

In August 2017, we performed a field-sampling campaign
to the Strytan hydrothermal field (Fig. 1A, B), and scientific scuba divers collected mineral precipitates from twoof the cones, Big Strýtan and Arnarnesstrýtan. Precipitates were taken by breaking off small, ∼15 cm × 5 cm,
pieces and placing them into sterile Whirl–pak bags
(Nasco, WI, United States). The samples were stored atfour degrees Celsius for transportation and finally driedat room temperature.

A glass Hell-Shaw cell of 15 mm thickness, 60 mm
width and 200 mm height was filled with an aqueous
solution of 1 M sodium silicate. An aqueous solutionof 1 M magnesium chloride was injected into this reactor by using a motorized syringe at a constant injection rate of 3 mL/hr, following the procedure reported
elsewhere (Sainz-Díaz et al. 2018). The experiment was
performed in a laboratory maintained at 20 °C. Demineralized and decarbonated water was used in all assays.

Gutiérrez‑Ariza et al. Progress in Earth and Planetary Science(2024) 11:11

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Fig. 1 Chimneys at the Strytan hydrothermal vent system (A), Sampling of solids and fluids (B). Close up of samples S1 (C) and S2 (D). Zones
identified in samples (E) S1; S1(tube) and S1(tip) are in yellow and green, respectively, and (F) S2; S2(top) and S2(bottom) are in yellow and green,
respectively

Gutiérrez‑Ariza et al. Progress in Earth and Planetary Science(2024) 11:11

For analysing the structures formed in this process,the solid was washed twice with water and dried at air
at 45 °C. Micrographs of these solids were obtained byusing a FEI-Quanta 400 environmental scanning electron microscope.

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3 Results
3.1 Field samples

Sample S1 has a light colour and is highly porous withlow density; the sample S2 has a greyish colour and ismore compact.

Fig. 2 SEM micrographs of Strytan vent sample S1, light in colour and highly porousGutiérrez‑Ariza et al. Progress in Earth and Planetary Science(2024) 11:11

In sample S1 many tubular structures were foundgrowing in disordered groups (Fig. 2A). In many cases
isolated rods are observed (Fig. 2B–F). Typical rhombohedral crystals of calcite morphology are found with anaverage size of 6–10 µm (Fig. 2C–E). This was confirmedwith EDX chemical analysis, which showed these crystals
are composed of calcium carbonate. They are coveredand surrounded by flaky solids that likely precipitatedlater. The chemical analysis of these flaky solids indicatedthat they are composed of magnesium silicate. The presence of some rods was detected with an average diameterof 2–5 µm (Fig. 2G–J). The microstructure of these rods
shows a compact centre and a flakier structure in theexternal surface (Fig. 2G-–J). This structural differenceindicates two possible growth regimes: one along the rod
length and another in a radial direction perpendicular
to the central compact rod. We cannot know from thisevidence alone, however, whether the regimes are simultaneous or consecutive. These rods can grow in straightforms and in periodic globular chains. At some points
along these chains isolated calcite crystals have formed,
stopping the chain growth in some cases (Fig. 2E).
In sample S2, the microstructure is different to that of
S1. No isolated calcite crystals are observed. Some tubular forms of 5–10 µm in diameter are observed (Fig. 3A–
C, H). Some rods similar to those found in sample S1 of adiameter of 2–3 µm (Fig. 3C–D) were found. The microstructure of these rods showed that nanorods of 100 nm
diameter grow radially, i.e., normal to the rods’ central
axes (Fig. 3E). The microstructure of some tubes indicates that globular aggregation units of 100–300 nm form
the tubular structure (Fig. 3F, G). Some microspheresof 1 μm are also observed; some of them forming disordered columns (Fig. 3F, G). In some zones compact crystals were observed (Fig. 3I) and other zones are coveredby layers of NaCl (Figs. 3J, 4c).
The chemical composition of the samples was determined in situ within the SEM with energy-dispersive
X-ray spectroscopy (EDX) analysis of the sample (Fig. 4).
In sample S1, carbonate crystals were observed (Fig. 4Aleft), whose rhombohedral morphology indicates calcite.
These crystals are surrounded by a thin layer of a highly
porous material presumed to be a magnesium silicate(Fig. 4A, right). In some zones a small amount of Al was
also detected in the magnesium silicate solids (Fig. 4B).
In sample S2, rods are surrounded by a highly porous
material identified as magnesium silicate. In some cases,
the relative Mg/Si proportion increases along with theoxygen content in the external border of this material(Fig. 4D left). These changes in the chemical content canbe assigned to the formation of magnesium hydroxidealong with silicate layers. In the external zones of magnesium silicate materials with a higher Al content has been

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observed (Fig. 4D, bright zones in the left zones), whereas
the internal zones the amount of Al is negligible (Fig. 4D,
bright zones in the right side). Since the vent fluid is thesource of aqueous A­ l3+, this change in precipitate composition from inner to outer would indicate a change inthe precipitation conditions (Fig. 4D). Some phases withlow porosity are identified as calcium carbonate andsodium chloride (Fig. 4C). Some rods are generated from
nuclei of calcium sulfate (Fig. 4F).
XRD data show that the S1(tip) sample has crystals ofaragonite and calcite (Fig. 5A) along with saponites of low
crystallinity showing broad peaks. The S1(tube) sample
shows calcite crystals and saponite (Fig. 5B). The S2(top)sample shows crystals of saponite and calcite (Fig. 5C).
Finally, sample S2(bottom) shows a similar composition,
but with more saponite (Fig. 5D).
The overall TEM pictures show some dense particles
surrounded by a disordered fringing material (Fig. 6A).
HRTEM micrographs showed layered morphology inmany particles of all samples. This material consists ofsmectite-like particles grown from the alteration of magnesium silicate precipitated from the alkaline waters, as
observed above in Fig. 6D. The layered particles correspond to aggregates of flakes, a few hundred nm or lessin size. They consist of aggregates of curved or folded
lamellar particles (Fig. 6B). The crystallinity of thesematerials is very low, and no small-angle electron diffraction (SAED) patterns could be obtained. In some cases,
spacings of 10 to 16 Å can be identified, with scarce lateral continuity and numerous stacking defects. These
spacings and the texture of the aggregates indicate thatthey are probably smectite lamellae (Fig. 6C). The darkparticles correspond to denser grains, with no apparent
internal structure, since in no case have lattice fringes ordiffraction patterns been observed. Probably these particles correspond to fragments of larger particles, whichhave been disaggregated during the sample preparation
procedure. They often present a reticulated and spongyrim, in which curved and folded lamellae are seen, similar to those observed in flaky particles. In some cases,
they also present lattice fringes corresponding to basal
spacings of smectite-like minerals. The images obtainedin ultrathin sections showed that the dense particles
without crystalline structure correspond to the interiorof large particles, which are externally surrounded by arim of smectite lamellae. This morphological evolution
suggests that the smectites were formed by a process ofalteration and precipitation involving previously formed
amorphous magnesium silicates. Spherical particles consisting of a core surrounded by lamellae, similar to thoseobserved in larger particles, were also observed (Fig. 6D).
Chemical analyses of individual particles or small
areas were obtained in STEM mode (Additional file 1:

Gutiérrez‑Ariza et al. Progress in Earth and Planetary Science(2024) 11:11

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Fig. 3 SEM micrographs of Strytan vent sample S2, grey in colour and compact

Table S1). Intensity ratios were recalculated as oxide
composition. The samples are mostly composed of Mg
and silica, with variable Al content, as well as minor
amounts of Fe, alkali and alkaline earth cations. Plotting

the analyses on a ­SiO2-(Al2O3 + ­Fe2O3)-MgO ternary
plot (Fig. 7), the dots are seen to be located next to the­SiO2-MgO line, with A­ l2O3 + ­Fe2O3 < 10%. Analyses offlaky structures are compatible with Mg phyllosilicatesGutiérrez‑Ariza et al. Progress in Earth and Planetary Science(2024) 11:11

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Fig. 4 EDX analysis of SEM images of field samples. a–b S1, c–f S2

Fig. 5 Powder X-ray diffraction patterns of the sample S1(tip) (A), S1(tube) (B), S2(top) (C), and S2(bottom) (D). Most of the reflections may be
assigned to aragonite (a), calcite (c), and saponite (s)of the saponite-stevensite type (Fig. 7, dark colour). The
calculation of the structural formulae was carried out on
non-homoionic (raw) samples, so that a part of the Mg
content should be located in the interlayer space as an
exchangeable cation. Structural formulas were estimatedon the basis of O
­ 10(OH)2, that correspond to half unit cellfor a smectite. Si and Al were assigned to the tetrahedral

layer up to 4 cations; the remaining Al together with Fe
and Mg were assigned to the octahedral layer up to 3. Fe
was estimated as Fe(III). Mg was divided between octahedral and interlayer positions using charge balance as acriterion. The composition of these particles is within alimited area that corresponds to the saponite-stevensite
smectites.

Gutiérrez‑Ariza et al. Progress in Earth and Planetary Science(2024) 11:11

Fig. 6 HRTEM micrographs of samples S1 (a–c) and S2 (d)The analyses of those particles that show neither crystal
arrangements nor layered morphology (Fig. 7, light colour) are divided into three groups. The first one includes
most of the analyses of S2(bottom) and some S2(top)particles, which are grouped in a narrow range of compositions (approximately S­iO2 60–63%, MgO 35–37%,­Al2O3 + ­Fe2O3 < 1%), close to the Mg-richer saponites.

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Most of the S1(tube) particles belong to the second
group and correspond to compositions richer in silica
than saponites and extended over a wide range of compositions ­(SiO2 65–80%, MgO 15–27, ­Al2O3 + ­Fe2O3 1.5–5.5%). In contrast, the third group comprises the analysis
of a few S2(top) particles. These particles are very rich insilica (72–76%), but the content of trivalent cations (13–16%) is much higher than that of MgO (3–8%).
These results indicate that the particles are composedof magnesium silicate, with an important variability of
the ratio between both elements, which reflects a certain
heterogeneity of the material. Other cations are in theminority, except for the third group already mentioned.
The heterogeneity of the composition of the clays in
the chimney can be seen in Fig. 8. This corresponds toa fragment with a dense core surrounded by lamellar
structures, as well as another deposit of small roundedparticles, smaller than 100 nm. All analyses have beenrecalculated as smectite structural formulas for comparison (Additional file 1: Table S1). The chemical analysis #4
of the core is compatible with a Mg smectite, although
its lack of internal structure and its morphology do notcorrespond to a smectite. Analyses #2 and #5 correspondto laminated textures and can be identified as saponite.
The slight positive octahedral charge may be due to partof the Mg occupying interlaminar positions. The analysisof the laminations in area #6 would be compatible witha very low charge stevensite, and a fraction of the Mg
could also occupy interlaminar positions. On the otherFig. 7 Ternary diagram and composition of the clay minerals found in the Strytan vent samples. Dark colour, layered particles; light colour, othermorphologies

Gutiérrez‑Ariza et al. Progress in Earth and Planetary Science(2024) 11:11

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With X-ray computed tomography, Fig. 9, we note how
the greyish sample S2 has a more compact structure withfewer and smaller pores showing thicker walls and amore robust construction than S1.
3.2 Laboratory chemical gardens

Similar flaky morphology is observed in chemical garden
materials formed in the laboratory with magnesium chloride solution injected into sodium silicate solution, being
mainly magnesium silicate with a high proportion ofmagnesium hydroxide (Fig. 10) (Sainz-Díaz et al. 2018).

4 Discussion
4.1 SHF chimneys compared to other vent types

Our investigations of the SHF field samples are consistent with previous literature regarding the presence ofsmectite/saponite clays, amorphous silica, gypsum, andcarbonates (Geptner et al. 2002; Price et al. 2017; Marteinsson et al. 2001; Stanulla et al. 2017). We additionallyreport the presence of magnesium hydroxide in the SHF
field samples. This has been reported at other alkaline
vents, including LCHF and Prony Hydrothermal Field(Proskurowski et al. 2008; Pisapia et al. 2017; and also
see Okumura et al. 2016a, b), but has not been previously detected in SHF chimneys (Price et al. 2017; Russell 2017). Though magnesium hydroxide may be difficult
to detect in these field samples, it makes sense that itshould form in this system, as it is seen in chemical-garden experiments of precipitation of Mg salts into silicate
solutions, where both Mg–silicate and Mg oxide/hydroxide are abundant in the resulting precipitates (Sainz-Diazet al. 2018; and Fig. 10).
The SHF chimneys also bear similarities to LCHF thatare relevant in an early-Earth context. The SHF chimneys have a microporous, labyrinthine interior structure(Fig. 9) that is similar to observed interior structures ofother alkaline vents such as LCHF (Kelley et al. 2005) or
Prony (Jones et al. 2020); and is different than chimneys

Fig. 8 HAADF analysis of chimney composition. Numbers
correspond to values in Table 1

hand, the analysis of area #1, with a laminar texture similar to #5 or #6, presents an excess of Mg that leads thecalculated formula to have a deficit of Si and Al. Finally,
the analysis of the rounded particles of area #3 shows anexcess of Si and a very high Al content, allowing a probable identification as a smectite.
The results of the punctual analysis show compositional
heterogeneity in the particles. The general composition ismagnesium silicate, with local predominance of Si or Mg,
and presence of other cations. The lamellar structures,
which can be assimilated to smectites, have low crystallinity and numerous lattice defects. In addition, between
the lamellae there are remains of the original amorphousmaterial or of cations leached during the alteration andformation of smectites. This may be the cause of smectite
particles whose structural formula has an excess or defectof cations.
Table 1 Chemical composition of points in particle in Fig. 8
Cation

1

2

3

4

5

6

Si

3.80

3.85

4.37

3.76

3.82

3.96

Al

0.16

0.16

0.96

0.49

0.28

0.18

Mg

3.11

2.99

0.38

2.53

2.87

2.76

Fe(III)

0.00

0.01

0.02

0.00

0.00

0.00

Na

0.00

0.00

0.49

0.14

0.00

0.00

K

0.00

0.01

0.19

0.03

0.00

0.01

Ca

0.05

0.04

0.06

0.13

0.06

0.04

Chemical analysis was converted to cations on the basis of ­O10(OH)2. Analyses 2, 4, and 5 are compatible with Mg smectites

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precipitate over time. The Strytan hydrothermal vent isa geological chemical garden, similar to Sainz-Diaz et al.
(2018) but with interior and exterior solutions reversedand different chemistry, where, driven by osmosis, highSi enriched vent fluid reacts and precipitates with cationsin the surrounding seawater. For slow osmosis, the wall
thickness of a chemical garden Lm over time is given by(Ding et al 2019):

L2m =Fig. 9 µCT slices showing the inner structures of S1 (top) and S2(bottom) samples

Fig. 10 A chemical garden formed in laboratory experimentsfrom 1 M Mg chloride and 1 M silicate solution (a) and an SEM image(b) of the internal surface of the material formedof black or white smokers, which exhibit denser, morecemented interiors with defined fluid flow conduits(Tivey and Singh 1997). This similarity between alkaline vents is likely due to the slower, diffuse flows that
occur in alkaline vent chimneys compared to the hotter,
faster flows that occur in the smoker vent chimneys (Von
Damm 1990).
In an origin-of-life context both the lifetime of theVent (i.e., the timeline for which the hydrothermal flow
remains active) and the rate of chimney growth (since
this determines its structure) are important. We can use
fluid mechanics to model the growth rate of the chimney

2Mkin po cSitµρS

here cSi is the concentration of the external silicate
solution, po is the osmotic pressure, kin is the permeability of the membrane in the regions of inflow, μ is the viscosity of the fluids, ρs is the precipitate density. For the
Strytan hydrothermal vent precipitates, calculating fromdata in the literature, the permeability is 0.4 × ­10–15 to­10–14 ­m2 (Price et al. 2017; Geptner et al. 2002), thus, taking a value in the middle of that range, allowing for calculation of the chimney wall growth rate. The osmoticpressure is calculated with consideration of all the ionsof sea water and vent water; the osmotic coefficientfor the sea water φ = 0.907, the vent water is dilute andφ = 1.0. We estimate the density of the rock, ~ 3 kg/L, as
10 times higher than the overall density of porous samples, 0.3–0.5 kg/L. We may compare this calculation withthe growth of black smoker and LCHF vent chimneys(Cardoso and Cartwright 2017), as shown in Fig. 11. We
find that Strytan will have faster growth compared withchemical diffusion of Lost City, but is still much slower
compared to a black smoker, which grows by thermal diffusion. The predicted growth rate of Strytan is compatible with a hypothesis that the cones could have started
growing at the end of the last glacial maximum, ~ 18 k yago; compare with the > 30,000 years predicted for the
LCHF (Früh-Green et al. 2005).

Fig. 11 Fluid-mechanical prediction of the growth of a Strytan ventover time in terms of wall thickness Lm (blue) compared with blacksmokers (grey) and LCHF (orange) vents

Gutiérrez‑Ariza et al. Progress in Earth and Planetary Science(2024) 11:11

4.2 SHF‑like vents in an early Earth context

An important issue for prebiotic early-Earth alkaline
vents is what types and chemistries of vents and chimneys were likely to be present, given different host rockand ocean composition. The basaltic host rock of the
Strytan vents is similar to typical mid-ocean ridge
basalts, MORB (Arnórsson et al. 2002; Price et al. 2017).
In contrast, the LCHF is produced by olivine-rich mantle
rock that is exposed to seawater during seafloor spreading at the mid-Atlantic ridge, yielding its alkaline fluids,
brucite/carbonate chimneys, and high concentrations of­H2 and ­CH4 (Kelley et al. 2001, 2005; Früh-Green et al.
2003). However, it is debated when plate tectonics began
and if it was operating on early Earth around the timeof the origin of life; this is important since it determines
the rock composition of the ocean crust that would formhydrothermal vents. On one hand, it has been argued
that Earth had an early onset of plate tectonics that
resulted in olivine-rich ocean crust that would facilitate
serpentinization, and thus, LCHF-like vents (Miyazaki
and Korenaga 2022; Debaille et al. 2013; Deng et al.
2023); alternatively, it has been argued that Hadean Earthwas in a stagnant-lid regime without geochemical cyclingfrom plate tectonics (Tarduno et al 2023). Komatiites,
MgO-rich igneous rocks that appear almost exclusively
in the Archean rock record, and form at hotter mantle
temperatures (Barnes and Arndt 2019; Takahashi and
Scarfe 1985; Grosch and Wilson 2023), may have beena predominant seafloor crust rock on the early Earth,along with other Archean basalts, which could have beenin some ways similar to modern MORB (Barnes andArndt 2019; O’Neil et al. 2012). There has been limited
experimental work on aqueous alteration of komatiite,
but a recent study has shown that ­H2 concentrations,as well as pH in komatiite-produced “hydrothermal fluids” increased at higher temperatures (~ 300 °C) (Ueda
et al. 2021), meaning that on early Earth, hotter ventswith black-smoker temperatures might have had pH andredox gradients similar to Strytan or LCHF. Anotherconsequence of early Earth’s hotter mantle is potential
seafloor shallowing leading to volcanic islands creating
exposed land mass (Rosas and Korenaga 2021); Archeanbasalt-hosted shallow vents could have also existed on
the coasts of volcanic islands (Barge and Price 2022).
The interface of alkaline hydrothermal fluid, rich in­OH−, ­Mg2+, and ­HS− (Mielke et al. 2010; White et al.
2020), with the early Earth’s ocean, anoxic, rich in dissolved ­Fe2+, ­SiO2, and ­CO2 (MacLeod et al. 1994; Halevy
and Bachan 2017; Tosca et al. 2016) would have resulted
in chimney precipitates containing minerals similar to
those at Strytan (Mg-silicates and clays, calcium carbonates, magnesium hydroxides), but also Fe-hydroxides,
Fe-carbonates, greenalite and/or silica gels, and perhaps

Page 12 of 15

Fe–Mg-containing clays (Ferris et al. 1986, Ferris 2005,
2006 Meunier et al. 2010, Russell 2018, 2017; Bargeet al. 2020; Tosca et al. 2016; Halevy et al. 2017). If theearly-Earth vents were, like Strytan, in shallow waters(e.g., Barge and Price 2022), then the chimney mineralogy could also have been influenced by photochemically
produced species. For example, N­ O3−/NO2− could have3+
acted as oxidants to produce F­ e from F­ e2+ (Wong et al.
2+
2017; Ranjan et al. 2019); or ­Fe could also have been
oxidized directly by UV radiation (Nie et al. 2017). This
would have resulted in precipitation not just of Fe(II)minerals, but also mixed-valence Fe(II,III) minerals,
including green rust (Russell 2018; Halevy et al. 2017).
Green rust, fougerite, has been proposed to be important for driving a variety of prebiotic reactions toward
the emergence of metabolism (Russell et al. 2018, 2023;
Branscomb and Russell 2013).
The metastable Fe-containing analogue of brucite (ferrobrucite) forms in serpentinizing systems even today(Templeton and Ellison 2020) and is theorized to haveexisted at LCHF-like vents on the early Earth (Trolard
et al. 2022). Our detection of magnesium hydroxide alongwith silicates in the Strytan chimneys is significant since
it implies that, in the early ­Fe2+-bearing oceans, Strytanlike chimneys would also contain iron-bearing mineralssuch as ferrobrucite or green rust, and could thus support LCHF-like prebiotic chemistry. Potential early-Earth
LCHF-like prebiotic reactions driven by Fe-hydroxideand Fe-sulfide minerals: e.g., carbon reduction, aminoacid synthesis, peptide formation, phosphorous chemistry, have been discussed at length in the literature (e.g.,
Russell 2023, 2018; White et al. 2015; Roldan et al. 2015;
Barge et al. 2019, 2020, Hudson et al 2020). However, incontrast to a LCHF-like chimney, a Strytan-like chimney
would additionally host reactions driven by silicate minerals such as Fe/Mg-clays (saponite), greenalite, and silica
gels. This could include aromatic amino acid synthesis by
Fe/Mg-saponites (e.g., Ménez et al. 2018); dehydration
and/or condensation reactions in silica gels (e.g. Westall
et al. 2018; Gorrell et al. 2017; Dass et al. 2018); or polymerization of RNA-type molecules catalysed by greenalite
particles (e.g. Rasmussen et al. 2021).

5 Conclusions
The Strytan field samples investigated in this work haveproperties of interest to prebiotic chemistry in a Strytanlike system on the early Earth. Similar to the pore structure of other alkaline vent chimneys, the Mg–silicate
chimneys are porous and contain a labyrinthine internal
structure. Chemical analysis of the chimneys is consistent with previous studies, demonstrating the presenceof clays and silicate minerals, but in this study we also

Gutiérrez‑Ariza et al. Progress in Earth and Planetary Science(2024) 11:11

detected Mg-hydroxide. This implies that Strytan-likevents on early Earth could have hosted LCHF-like prebiotic chemistries driven by iron-containing magnesiumhydroxide and/or perhaps other Fe-hydroxides. Thus
Strytan may be an even higher-fidelity early-Earth analogue than the LCHF, because of its basalt host rock.
Further studies of the SHF and other basalt-hosted vents,
as well as further laboratory experiments simulating the
growth of hydrothermal chimneys, can continue to shedlight on the prebiotic reactions that could have beenfavoured in these kinds of systems.

Supplementary Information
The online version contains supplementary material available at https://​doi.​
org/​10.​1186/​s40645-​023-​00603-w.
Additional file 1. Table S1. Chemical composition (in oxides wt%) ofparticles analysed by TEM-EDS.
Acknowledgements
This research was supported in part by the ELSI Origins Network (EON), which
was supported by a grant from the John Templeton Foundation. REP acknowl‑edges NASA Habitable Worlds Program Grant Nos. 80NSSC20K0228 and
80NSSC24K0076. SEM acknowledges JSPS KAKENHI Grant No. 22K18278. LMB’s
work was performed at the Jet Propulsion Laboratory, California Institute ofTechnology under a contract with NASA (80NM0018D004). This research was
funded in part by Spanish FEDER/Junta de Andalucía‐Consejería de Economíay Conocimiento grant PY20_01389. We acknowledge the contribution of the
COST Actions CA17120, Chemobrionics and CA21169, Dynalife, supported by
European Cooperation in Science and Technology.
Author contributions
Conception and design: SEM, CISD, JHEC; Sample collection: SEM, DG, RP;
Data analysis, curation, methodology: CGA, LMB, YD, SSSC, SEM, RN, DG, RP,
FJH, CISD, JHEC; Visualization: CGA, YD; Wrote the initial manuscript draft: LMB,
CISD, JHEC; Organized the expedition and acquired funding: SEM; Interpreta‑tion, review, editing: LMB, SSSC, SEM, DG, RP, FJH, CISD, JHEC.
Funding
Open Access funding provided thanks to the CRUE-CSIC agreement withSpringer Nature. This research was supported in part by the ELSI Origins
Network (EON), which was supported by a grant from the John Templeton
Foundation. REP acknowledges NASA Habitable Worlds Program Grant Nos.
80NSSC20K0228 and 80NSSC24K0076. SEM acknowledges JSPS KAKENHI
Grant No. 22K18278. LMB’s work was performed at the Jet Propulsion
Laboratory, California Institute of Technology under a contract with NASA
(80NM0018D004). This research was funded in part by Spanish FEDER/Junta
de Andalucía‐Consejerí de Economí y Conocimiento grant PY20_01389. We
acknowledge the contribution of the COST Actions CA17120, Chemobrionics
and CA21169, Dynalife, supported by European Cooperation in Science andTechnology.
Availability of data and materials
The materials used and/or analysed during the current study are available
from the corresponding author on reasonable request.

Declarations
Competing interests
We have no competing interests.
Received: 20 September 2023 Accepted: 21 December 2023

Page 13 of 15

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