Читать книгу EXTREMOPHILES as Astrobiological Models - Группа авторов - Страница 20

Samples of steam were collected from fumaroles in four permanently protected geothermal areas, Lassen Volcanic National Park, Hawai’i Volcanoes National Park, Valles Caldera National Preserve, and Solfatara Crater, Italy (Table 1.1). Our Hawai’i Volcanoes National Park sites are coded, as part of our collection agreement with the park. These sites have a wide and interesting variety of chemical steam caves and vents not seen in other geothermal areas. Our choice of Hawai’i as a site with an active volcano proved to be interesting. In many ways, its basaltic lava flows resemble those of our nearby planet Mars, both chemically and physically providing a match for using Earth’s extremophile life as a model for life on other planets. Mars is one of those planets close enough for experimental approaches and applications.

In active steam caves, meteoric waters characteristically descend through porous and fractured surface lava and eventually meet upward convection of heat and rising volcanic gases. Heat generates abundant steam that rises as a vapor-gas mixture through fractured lava crevices and fissures towards the surface. Near the surface, passageways—both horizontal and vertical—allow the vapors to condense on the cooler cave ceilings and walls, depositing characteristic chemical signatures and forming a matrix-like material rich in nutrients for extreme microorganisms. The steam exits the cave or vent opening and provides a diffused smoke-like flow known as a fumarole. Venting steam commonly proceeds in an artesian or burst flow. With large volumes of steam, visibility of the cave interior or vent opening can be obscured. Steam cave/vent openings can be small on the order of a few centimeters or large, one to three meters or larger for wide steam vents or vertical caves. Our selection of steam caves was based on the idea that while we and others [1.7] [1.10] [1.12] [1.16] had already investigated and identified organisms, especially Archaea in steam vents, there was not much information on organisms from those steam caves/vents regarding their in-situ appearance and some of the sites where they have previously been isolated left gaps in our information on the physical appearance of steam vent microorganisms at the structural level.