Cua­tro Ciéne­gas Basin, Coahuila.

Cua­tro Ciéne­gas Basin (CCB) is located in the Chi­huahuan Desert of Coahuila in north cen­tral Mex­ico. Within the basin, a large num­ber of highly diverse springs (>300), spring-​fed streams and ter­mi­nal evap­or­itic ponds form an inverse arch­i­pel­ago, in which aquatic sys­tems are sep­a­rated by sparse desert veg­e­ta­tion, micro­bial crusts and salty soils. Stud­ies indi­cate that much like the finches, tor­toises and other mac­ro­biota of the Gala­pa­gos Islands, a rich and diverse web of unique local diver­sity is weav­ing in response to the par­tic­u­lar cir­cum­stances of this desert val­ley (Souza et al., 2008).

The rel­e­vance of CCB for Astro­bi­ol­ogy is that it may be a proxy for the late Pre­cam­brian when eukary­otic organ­isms diver­sify and became more com­plex. CCB could rep­re­sent an extant eco­log­i­cal “time machine” sug­ges­tive of ear­lier times in Earth’s his­tory and by exten­sion, other sim­i­lar extrater­res­trial planet bod­ies dur­ing their pale­oe­co­log­i­cal past (Souza et al., 2011). It is expected that CCB har­bors biosig­na­tures of past and present life that can be used in our search for extrater­res­trial life (Siefert, 2011). More­over, CCB has been sug­gested as the most anal­o­gous tar­get to Gale crater from the MSL/​Mars 2018 mis­sion (Souza et al., 2011). A spe­cial issue about this site is presently in press in Astro­bi­ol­ogy (Vale­ria Souza, per­sonal communication).

Cua­tro Ciéne­gas Basin research is presently led by Dr. Vale­ria Souza (Insti­tuto de Ecología, UNAM) who closely col­lab­o­rates with the Ari­zona State Uni­ver­sity NAI team and the Vir­tual Plan­e­tary Laboratory.

Guay­mas Basin, Gulf of Cal­i­for­nia.

The Guay­mas Basin is located between the states of Sonora and Baja Cal­i­for­nia in the Gulf of Cal­i­for­nia. Guay­mas is a spread­ing axis that dif­fers from the plate bound­ary zones at the mid ocean ridges because seafloor erup­tions are inhib­ited by rapid depo­si­tions of low-​density sed­i­ments (Lond­slade and Becker, 1985). The Basin is a hydrother­mally active envi­ron­ment that includes vent plumes, seeps, and anoxic sed­i­ments, each of them exhibit­ing a wide range of tem­per­a­tures. This envi­ron­ment sup­ports surface-​attached micro­bial mats, diverse prokary­otic and eukary­otic microbes, and symbiont-​harboring inver­te­brates. Warm, sul­fide– and hydrocarbon-​rich, anaer­o­bic sed­i­ments accu­mu­late at a rate of 1 – 2 mm/​year because of the high bio­log­i­cal pro­duc­tiv­ity in the water col­umn and a large ter­rige­nous input from Baja and the Mex­i­can main­land (Edg­comb et al., 2002).

The hydrother­mal envi­ron­ment of the Guay­mas Basin serves as a model sys­tem to study anaer­o­bic micro­bial com­mu­ni­ties (methane oxi­diz­ers, and sul­fate reduc­ers) that cat­alyze a sulfate-​and methane-​driven anaer­o­bic car­bon cycle that is com­pat­i­ble with sta­ble car­bon and sul­fur iso­tope evi­dence for early Earth ecosys­tems (Teske et al., 2003). As other hydrother­mal sys­tems, the Guay­mas Basin is a test bed for micro­bial ecosys­tems analogs for the Jupiter satel­lite, Europa.

The Guay­mas Basin is presently stud­ied by Dr. Elva Escobar-​Briones head of the Bio­di­ver­sity and Macro­e­col­ogy Lab­o­ra­tory (Insti­tuto de Cien­cias del Mar y Lim­nología, UNAM), and was explored by the Marine Bio­log­i­cal Lab­o­ra­tory, NAI team (2003−2008).

Alchichica Lake, Puebla

Alchichica is a crater lake located in the Ori­en­tal Basin at the bor­der of the states of Puebla, Tlax­cala and Ver­acruz. It is sit­u­ated at an alti­tude of 2,300 m above the sea level with a max­i­mum depth of 64 m (Escobar-​Briones et al. 1998). The lake is hypos­aline (8.5−10 g/​liter) and alka­line (pH 8.9−9.1) with sodium and chlo­ride being the dom­i­nant ions but also with bicar­bon­ate and car­bon­ate ions (Navarro et al, 2010). These con­di­tions are favor­able for active car­bon­ate depo­si­tion that results in the for­ma­tion of dis­tinc­tive stro­ma­to­lite struc­tures in the lit­toral region of the lake.

Despite their geo­log­i­cal and evo­lu­tion­ary impor­tance, the pre­cise stro­ma­to­lite for­ma­tion mech­a­nisms remain poorly under­stood and this site is one of a few in the world where the role of microor­gan­isms and envi­ron­men­tal con­di­tions for stro­ma­to­lites for­ma­tion can be stud­ied (Couradeau et al., 2011). There­fore, this site is cru­cial to the under­stand­ing of the most ancient struc­tures formed by bio­log­i­cal activ­ity and rel­e­vant for Astro­bi­ol­ogy stud­ies. On the other hand, the Alchichica crater-​lake has been pro­posed for the study of bio­mark­ers for the search of life on Mars (Navarro et al., 2010).

The site has been stud­ied by Dr. Javier Alco­cer (Fac­ul­tad de Estu­dios Supe­ri­ores, Izta­cala, UNAM), Dr. Elva Esco­bar Briones (Insti­tuto de Cien­cias del Mar y Lim­nología, UNAM), Dr. Luisa Fal­cón (Insti­tuto de Ecología, UNAM), and more recently by the group led by Dr. Rafael Navarro-​González who col­lab­o­rates with Dr. Christo­pher McKay (NASA Ames Research Center).

Guer­rero Negro, Baja Cal­i­for­nia.

Guer­rero Negro, the largest town located in the munic­i­pal­ity of Mulegé in the state of Baja Cal­i­for­nia Sur, is known for its salt works. The first salt mine was estab­lished in 1957 around the Ojo de Liebre coastal lagoon The com­pany even­tu­ally became in Expor­ta­dora de Sal, S. A. (Salt Exporters, Inc.), the great­est salt mine in the world.

Com­mer­cial salt ponds in Guer­rero Negro pro­duce methane gas whose iso­topic sig­na­tures may help sci­en­tists to under­stand the ori­gin of methane in Mars atmos­phere. Iso­topes are a key to under­stand­ing the ori­gin of methane because organ­isms tend to use more of the lighter iso­topes. Bio­genic methane usu­ally, but not always, con­tains a higher per­cent­age of the lighter carbon-​12 than non-​biogenic methane, which con­tains rel­a­tively more of the heav­ier carbon-​13 (Pot­ter et al., 2009; Har­ris et al., 2012).

The salt flats of Guer­rero Negro are an excel­lent out­door lab­o­ra­tory because pools of increas­ing salin­ity are cre­ated as ocean water is evap­o­rated to con­cen­trate the salt. Car­bon and hydro­gen iso­topes of the methane found in the Area 9 com­prise “a pretty unique sig­na­ture,” which falls out­side the accepted range of bio­genic methane, and thus begs for a more com­plete expla­na­tion, says iso­tope expert Jeff Chan­ton, a pro­fes­sor of Oceanog­ra­phy at Florida State Uni­ver­sity. For that rea­son alone, the salt ponds in Baja are worth study­ing.

Dr. David Des Marais and his col­leagues, from the NASA Ames Research Cen­ter in Moun­tain View (CA), have stud­ied micro­bial mats of a series of salt evap­o­ra­tion ponds that run along the Pacific shore­line near Guer­rero Negro. They believe the mats may hold impor­tant clues to what life was like on early Earth. They also hope to gain insight into how to search for signs of life on plan­ets around dis­tant stars. Only in cer­tain extreme envi­ron­ments it is pos­si­ble to find nearly pure micro­bial ecosys­tems. Guer­rero Negro is a suit­able place for that because the water in the evap­o­ra­tion ponds there is so salty that micro­bial mats can com­pete suc­cess­fully. The mats under study live in water 2 to 3 times as salty as sea­wa­ter (Hoehler et al., 2001; Vogel et al., 2009).

Cenote ‘El Zacatón’, Tamauli­pas.

El Zacatón, the world’s deep­est known water-​filled sink­hole or cenote, was formed dur­ing the Pleis­tocene as a result of vol­canic activ­ity from below. The caves and sink­holes of the Zacatón sys­tem are spread across Ran­cho La Azufrosa near the small town of Aldama in the north­east­ern side of the state of Tamauli­pas, roughly 32 kilo­me­ters from the Mexico’s Gulf Coast.

El Zacatón cenote is a deep, cylin­dri­cal shaft about 100 meters wide and more than 300 meters deep that has been called an “upside down Mount Ever­est”. El Zaca­ton offers a diver­sity of micro­bial life that varies with depth in a geo­met­ri­cally unknown set­ting, mak­ing the cenote a per­fect place to test autonomous life form detec­tion, dis­crim­i­na­tion, and col­lec­tion. Research per­formed in that area will help sci­en­tists to deter­mine the phys­i­cal and chem­i­cal processes that have formed this unique and immense cave sys­tem, as well as arrive to a bet­ter under­stand­ing of how microbes live in extreme envi­ron­ments and develop tech­nol­ogy that might some­day aid the search for life beyond Earth (Sahl et al., 2010).

El Zacatón has been inves­ti­gated by the Deep Phreatic Ther­mal Explorer (DEPTHX) team, a NASA’s ASTEP funded Project. DEPTHX is a com­pletely autonomous robotic probe designed as a pro­to­type vehi­cle that might some­day explore the deep ocean under the icy crust of Jupiter’s moon Europa look­ing for signs of life there (Kra­jick, 2007).

Dr. John Spear (Col­orado School of Mines), the lead micro­bi­ol­o­gist on the DEPTHX team, spec­u­lates that this deep chan­nel is con­nected to an under­ground sys­tem of ther­mally heated water. About one mil­lion years ago, geol­o­gists believe, the region of El Zacatón was a site of intense hydrother­mal activ­ity. Although that hydrother­mal activ­ity has con­sid­er­ably calmed down, there are clear signs that some­thing is still stir­ring under­ground: a per­va­sive scent of sul­fur hov­ers around the cenote, and water at a con­stant tem­per­a­ture of 30 degrees Cel­sius sug­gests an unusu­ally well-​mixed environment.

Los Azufres, Michoacán.

Los Azufres is one of the main geot­her­mal Welds of the coun­try. It is located within a sili­cic vol­canic com­plex in the Trans-​Mexican Vol­canic Belt (TMVB) at the Michoacán state West Mex­ico. Los Azufres rep­re­sents the sec­ond most impor­tant geot­her­mal field in Mex­ico for the gen­er­a­tion of elec­tric power, mainly, by a com­pany cre­ated and owned by the Mex­i­can gov­ern­ment, the Fed­eral Elec­tric­ity Com­mis­sion (CFE).

In its nat­ural state, the Los Azufres geot­her­mal field con­sists of a deep aquifer where the ascend­ing fluid starts boil­ing at about 1200 m a.s.l. The two phase liq­uid dom­i­nant region extends upwards from 1200 m a.s.l. to about 1700 m a.s.l. where steam becomes the dom­i­nant phase. The two phase steam dom­i­nated region extends up to about 2400 m a.s.l. where a region of dry or super­heated steam is located. The pH of flu­ids is neu­tral with val­ues between 5.5 and 7.4, and the tem­per­a­ture of flu­ids can reach more than 300°C (Bar­ragán et al., 2005).

The most impor­tant hydrother­mal min­er­als occur­ring at the Los Azufres geot­her­mal sys­tem are: chlo­rite, pyrite, hematite, epi­dote, cal­cite, albite, adu­laria, zeo­lite and quartz which were formed by alter­ation of pri­mary min­er­als: olivine, pyroxene/​amphiboles, biotite, feldspar and rock-​matrix. Besides increased salt con­cen­tra­tion of the NaCl-​type brine, the fluids from the Los Azufres reser­voir are con­sid­er­able enriched in B, Si, As, F, Rb, Cs, Sr, Mo, Se and W (in decreas­ing order). With val­ues up to 24 000 mgL−1 and 560 000 mgL−1, the ele­ments As and B exceed hun­dred to thou­sand fold the inter­na­tional drink­ing water stan­dards (Birkle and Merkel, 2000). Thus, the geot­her­mal field of Los azufres is known as one the places with the max­i­mum nat­ural arsenic con­cen­tra­tions in Amer­i­cas (up to 24 mg L−1), when com­pared, for exam­ple, to the geot­her­mal springs of Yel­low­stone National Park in US and to El Tatio Lake in North Chile.

The char­ac­ter­i­za­tion of hiperther­mophilic microor­gan­isms liv­ing on Los Azufres has been very recently started by a wide range of Mex­i­can sci­en­tific groups led by Dr. Esper­anza Martínez-​Romero (Cen­ter for Genomic Sci­ences, UNAM), Dr. Georgina E. Reyna-​López (Uni­ver­si­dad de Gua­na­ju­ato) (Rodriguez-​Cuevas et al., in prepa­ra­tion), and Dr. Jesús Campos-​García (Uni­ver­si­dad Michoa­cana de San Nicolás de Hidalgo).

‘Del Azufre’ and ‘Luna Azufre’ Caves, Tabasco.

Cueva del Azufre, also known by the locals as “Cueva de la Sar­dina” or “Cueva de Villa Luz”, is a cav­ern located in the south­ern state of Tabasco, in the Cre­ta­ceous lime­stone within the regional park of Kolem Jaa, near the small town of Tapi­ju­lapa. Cueva del Azufre is a mod­er­ate sized cave (2 kilo­me­ters of pas­sage) with numer­ous cham­bers and sky­lights. What makes it so dif­fer­ent is the strong smell of rotten-​eggs from hydro­gen sul­fide (H2S), which stems from nat­ural vol­canic sources. Both the pres­ence of H2S and the absence of light exert strong selec­tion on organ­isms exposed to them. Hydro­gen sul­fide is acutely toxic to most meta­zoans and leads to extreme hypoxia in the water. How­ever, the cave pas­sages are teem­ing with life based on the oxi­da­tion of H2S. Thus, Cueva del Azufre con­tains an extra­or­di­nar­ily diverse pop­u­la­tion of microbes. Sul­fate reduc­ing bac­te­ria are present in very high num­bers within the pores of rocks, which can run miles deep. These sulfur-​eating bac­te­ria form slen­der white mucus-​like colonies on the cave ceil­ings and walls. These micro­bial veils have been nick­named by researchers as “snot­tites” (pH 0 – 1 biofilms). Addi­tion­ally, other sticky clus­ters of microbes, also face­tiously named “phlegm balls” can be observed float­ing in sub­ter­ranean streams of the cave (Hose and Pis­arow­icz, 1999).

Despite its name, Cueva Luna Azufre is a non­sul­fidic cave. It is smaller than Cueva del Azufre. Although the two caves are in close prox­im­ity, they are located within dif­fer­ent hills that are sep­a­rated by a sur­face val­ley. The creek in the Cueva Luna Azufre is also fed by springs; how­ever, these do not con­tain H2S (Tobler et al., 2008).

Cave micro-​organisms are eas­ier to access ver­sus their geo­log­i­cally com­pa­ra­ble coun­ter­parts in deep-​sea vents or Mars. The snot­tites biofilms are sus­pected of being able to flour­ish beneath Mars’s rocky sur­face that con­tains water resources to sus­tain this type of microbes (Nadis, 1997). Because of the dis­cov­ery of the microbial-​rich com­mu­nity below Earth’s sur­face, astro­bi­ol­o­gists now believe that look­ing into Earth’s caves can lead to greater knowl­edge of life on present-​day and pre-​historic Mars. Many of the unique and bizarre microbes encoun­tered within the extreme envi­ron­ment of both caves are newly dis­cov­ered and yet-​to-​be-​identified. Jen­nifer Macal­ady (Penn­syl­va­nia State University,NAI team) has recently started to study the micro­bi­ol­ogy in both caves through metagenomics.

Bacalar Lagoon is a 40 km long and 1 to 2 km wide, NNE-​trending fresh­wa­ter lagoon located in south-​eastern Quin­tana Roo, Mex­ico. Bacalar is also known by locals as “Lagoon of the seven col­ors” given that it is pos­si­ble to dis­tin­guish a range of seven shades of blue cor­re­spond­ing to the flows from seven dif­fer­ent cenotes. It is sur­rounded by flat-​lying Ceno­zoic lime-​stone. The out­line of Bacalar Lagoon, adja­cent lagoons and for­mer river beds sug­gests the influence of tec­tonic grain in the area. Bacalar Lagoon gets as deep as 15 m. Along large parts of the lagoon, shal­low, inter­mit­tently flooded areas with plant growth sep­a­rate Bacalar into a west­ern sec­tion and an east­ern sec­tion. Water tem­per­a­tures range from 25 to 28 °C. Ca2+ con­cen­tra­tions are close to typ­i­cal val­ues of marine waters and HCO3 val­ues even exceed aver­age marine con­cen­tra­tions. These high ion con­cen­tra­tions are pre­sum­ably a con­se­quence of dis­so­lu­tion of lime­stone bedrock and water cir­cu­la­tion in a con­nected karst sys­tem (Gis­chler et al., 2008).

With more than 10 km of total length, Holocene micro­bialites in Bacalar Lagoon belong to the largest fresh­wa­ter micro­bialite occur­rences. Micro­bialites are among the old­est traces of life on Earth and known from deposits as old as early Archaean (Rid­ing, 2000; All­wood et al., 2006).

Micro­bialites from Bacalar Lagoon include domes, ledges and onco­l­ites. The micro­bialites of Bacalar lagoon have been recently under the study of Dr. Eber­hard Gis­chler (Insti­tut für Geowis­senschaften, J.W. Goethe-​Universität, Ger­many) and Dr. Luisa I. Fal­cón (Insti­tuto de Ecología, UNAM) (Bel­trán et al., 2012).

Rincón de Parangueo, a recently dis­se­cated crater lake from the vol­canic com­plex of Cen­tral Mex­ico, rep­re­sents an extreme envi­ron­ment where micro­bialites dis­trib­ute irreg­u­larly along the exter­nal facies of the for­mer crater-​lake. Rin­con de Parangueo is one of seven crater-​lakes (com­monly called as “the hole”) local­ized north of Yuriria Lake in the state of Gua­na­ju­ato (Chacón et al., 2009).

The pre­dom­i­nant veg­e­ta­tion types of Rin­con de Parangueo are sub­trop­i­cal scrub and trop­i­cal decid­u­ous for­est. There is a peren­nial lake inside the crater, which pro­vides an abun­dance of Burs­era excelsa and Con­zat­tia mul­ti­flora. The lake is one of the few nat­ural places of trop­i­cal decid­u­ous for­est, par­tic­u­larly because its loca­tion inside a crater.

A pre­vi­ous short report (Chacón et al., 2003) showed extreme geo­chem­i­cal con­di­tions, such as high pH (10) and high salin­ity in which only spe­cial micro­bial life could inhabit. These stro­ma­tolitic mounds pile up in reg­u­lar groups vary­ing in their indi­vid­ual sizes. They show a fine lam­i­na­tion within the first 2 mm of sur­face, fol­lowed by a coarser tex­ture, exhibit­ing a typ­i­cal stro­ma­tolitic micro­fab­ric in thin sec­tions.

A research led by Dr. Eliz­a­beth Chacón (Fac­ul­tad de Cien­cias de la Tierra, UANL) has pre­lim­i­nary results derived from dif­fer­ent analy­sis under progress sug­gest­ing both, a bio­genic and abio­genic inputs in the con­struc­tion of Rin­con de Parangueo car­bon­ates (Chacón et al., 2009). The micro­bialites from Rin­con de Parangueo offer thus an intrigu­ing exam­ple of recent micro­bialites from fresh­wa­ter set­tings that may help to clar­ify the role of microor­gan­isms in the con­struc­tion of ancient and recent microbialites.

Figueroa Lagoon (a.k.a. Mor­mona Lagoon) became famous for its thick micro­bial mats that have been stud­ied from ample dif­fer­ent per­spec­tives since the mid 1970’s (Horodyski and Von­der Haar, 1975; Horodyski et al, 1977; Horodyski, 1977). It is a closed, hyper­saline lagoon, located 163 km south of Ense­nada, formed by a sand bar­rier with an approx­i­mate length of 20 km. The lagoon is almost com­pletely filled with sil­ica par­ti­cles and gyp­sum. It con­sists today of a nar­row strip of marsh flats and a vast evap­o­ra­tion plain. The main source of water is the ocean, seep­ing through the dunes at high tide and form­ing per­ma­nent pud­dles or ephemeral pools that mea­sure from sev­eral meters to hun­dreds of meters in diam­e­ter. Its approx­i­mate size is 59 hectares. Lam­i­nated micro­bial mats at this site offer a unique nat­ural lab­o­ra­tory where it is pos­si­ble to study all aspects of these micro­bial ecosys­tems.

The Lagoon was stud­ied by Tazaz et al (2012) for redefin­ing the iso­topic bound­aries of bio­genic methane in order to avoid the pos­si­bil­ity of false neg­a­tives returned from mea­sure­ments of methane on Mars and other plan­e­tary bod­ies. This study was coau­thored by Brad M. Bebout cur­rent mem­ber of the NASA Ames Research Cen­ter NAI team.

Located in the mid­dle of the Lacan­dona Rain­for­est is char­ac­ter­is­tic for its high lev­els of met­als like Cr, Ni, Zn, and Hg (Hansen, 2012).

Ther­mal springs: In Mex­ico there are more than 100 ther­mal springs dis­trib­uted along the coun­try asso­ci­ated to tec­ton­i­cally active regions (Prol-​Ledesma and Juárez, 1986).

Is the most exten­sive desert in North Amer­ica. Fos­sils found on this site include mol­luscs, insects and dinosaurs.

A strato-​volcano located between the states of Ver­acruz and Puebla. It has the higher trop­i­cal tree­line (~4000 m) in the world that is presently used to study a pine (Pinus hartwegii) that may be use­ful to ter­raform Mars (Molina-​Sevilla et al. 2008). In this site were iden­ti­fied four novel psy­chrophilic, ion­iz­ing radiation-​sensitive Deinococ­cus species (Cal­le­gan et al. 2008).

It is a shal­low warm mesos­aline soda-​alkaline lake located at the crater of an extinct strato-​volcano in the basin of Ori­en­tal in the cen­ter of Mex­ico (Alco­cer et al. 1999).

 Open-​air pit cave located in the state of San Luis Potosí. The floor of the cave is a 370-​meter free fall drop from the high­est side of the opening.

Located in the state of Chi­huahua is a giant geode with 10 m selen­ite crys­tals. The tem­per­a­ture in the cave varies from 45°C to 50°C, while the per­cent­age of humid­ity ranges from 90 to 100% (http://​www​.naica​.com​.mx/).