Tag Archives: continental crust

Life found deep in the oceanic crust for the first time

For the first time in history, researchers have found microbes living deep inside Earth’s oceanic crust – the black basalts that make some 60% of our planet’s surface – potentially the largest habitat on our planet.

Engineering and microbes

navaMicrobiologist Mark Lever is on board the Integrated Ocean Drilling Program’s research vessel JOIDES Resolution to examine rock samples from the depths – and the engineering problems are numerous. Drilling beneath 2.5 km of water and hundreds of meters of sediment and then onto the crust is no easy feat.

They drilled through 265 metres of sediment and 300 metres of crust to collect (geologically) young basalts that were formed some through 265 metres of sediment and 300 metres of crust to collect samples which contained microbes that metabolize sulphur compounds and some that produce methane.

So how do the microbes survive down there? The key is a process called chemosynthesis; you’ve most likely heard of photosynthesis, which is the process through which plants use sunlight to gain energy. Well chemosynthesis does the same thing, but uses chemical instead of solar energy. It is basically the biological conversion of one or more carbon molecules (usually carbon dioxide or methane) and nutrients into organic matter using the oxidation of hydrogen (or other inorganic molecules). Chemosynthesis also fuels other unlikely places which harbor life, such as hydrothermal vents.

chemosynthesis

The thing is, the oceanic crust is relatively homogeneous as a habitat throughout our planet, and if you find microbes at one site, the odds are you’re gonna find them throughout its entire extent. If this is indeed the case, the crust “would be the first major ecosystem on Earth to run on chemical energy rather than sunlight”, says Mark Lever, an ecologist at Aarhus University in Denmark, who led the study.

An unlikely habitat

“This study is highly significant in that it confirms the existence of a deep-subsurface biosphere that is populated by anaerobic microorganisms,” says Kurt Konhauser, a geomicrobiologist at the University of Alberta in Edmonton, Canada.

oceanic crust1

Oceanic crust is called this way well, because it’s typically under the oceans. It is much thinner than continental crust and it is constantly formed at spreading centres on oceanic ridges. To put it this way, it’s not an oceanic crust because there is an ocean above it, there’s an ocean above it because it’s an oceanic crust. It consists of several layers, the topmost which is usually 0.5 km thick, made of basalts.

The team included scientists from six different countries. To test if the microbes were still active, the team heated the rock samples to 65 °C in water rich in chemicals found on the sea floor. Over time, more and more methane was produced, showing that the little buggers were still well and active.

Lever is convinced that the microbes are not just accidentally there, hitching a ride from someplace else – despite initial doubts.

“When I went on this expedition, I thought it would be impossible to get contamination-free samples,” he says.

He changed his opinion quickly after analyzing the samples. The team had added small amounts of marker chemicals to the fluid they used to drill for samples, but although they basically painted the outside with this fluid, the rocks were so compact that none of it reached the inside. Lever now plans to analyse fragments of crust collected from other sites in the Pacific Ocean and the north Atlantic. We’ll keep you posted with any future updates on the matter.

“Given the large volume of sub-sea-floor crust, one can’t help but wonder how the amount of living biomass there compares to that at the Earth’s surface,” says Konhauser.

Via Nature

Tectonics on Enceladus

As you may or may not know, we’ve launched a new section of our website: Science Questions and Answers – a section aimed at you guys, where you can ask all questions science-related, and share your knowledge with others. We’re still in the beta version, but please, feel free to ask away – we’ll do our best to answer, answer, and vote.

So recently, somebody asked about tectonics on Enceladus. How does tectonics even work on a satellite like Enceladus? Well…

Plate tectonics

plate tectonics

Plate tectonics is a theory that emerged in the 1970s, as an attempt to describe the large-scale motions of Earth’s lithosphere. Basically, the litosphere of the Earth is composed of distinct rigid plates, comprising of continental crust or oceanic crust. These plates are in a continuous relative movement.

enceladus tectonics 1

Plate tectonics is, at its very basic level, a kinematic phenomenon. Generally, it is accepted that tectonic plates are able to move because of the relative density of oceanic lithosphere and the relative weakness of the asthenosphere, but there is still a lot of debate here. The energy is provided by dissipation of heat from the mantle through convection currents; how mantle convection relates directly and indirectly to the motion of the plates is a matter of ongoing study and discussion in geodynamics.

Enceladus tectonics

enceladus tectonics 2

Enceladus is a moon of Saturn, with a mean diameter of 505 kilometers, seven times smaller than the Earth’s Moon; it is covered in ice, but seems to have considerable amounts of water beneath its frozen surface. The surface is so cold that instead of traditional volcanoes, the surface of Enceladus is riddled with cryovolcanoes – volcanoes that erupt volatiles such as water, ammonia or methane, instead of molten rock.

Voyager 2 provided the first signs of tectonics on Enceladus; troughs, scarps, and belts of grooves and ridges were all observed. Perhaps the most shocking evidence was rifts; a rift is a linear zone where the litosphere is being bulled apart by tectonic forces. Observed canyons are up to 200 km long, 5–10 km wide, and one km deep. These features are relatively young and seem active.

Another evidence of tectonics is the grooved terrain; the surface of Enceladus is scarred with curvilinear grooves and ridges which often separate smooth areas from impact craters. Other tectonic features include numerous fractures on the surface of the moon. All in all, the geodynamic evidence is pretty convincing, but there’s even more.

enceladus stripes

Recent data from the Cassini spacecraft highlighted, aside from the prominent tectonic features, intense heat flow and geyser like plumes. Therefore, in the deeps of Enceladus, there lies a significant source of heat. Even a tiny, icy moon like Enceladus can develop complex surficial geomorphologies, high heat fluxes, and geyser-like activity, even without convection currents – which raises an interesting discussion about Earth’s tectonics, but that’s a different story.

Exobiology implications

Not entirely related to the question… but. If the satellite has a hot core and an icy surface, it’s only logical that it has a liquid water habitat inside, which is actually quite likely to host life! Researchers and exobiologists in particular are speculating a lot on this matter, and Enceladus is one of the top candidates for extraterrestrial life in our solar system.