Tag Archives: oceanic crust

oceanic-crust

Oldest oceanic crust might have been part of the Tethys Ocean 340 million years ago

oceanic-crust

Credit: Google Earth

It’s hard to think we’re talking about the same planet when we see snapshots of Earth’s geological past. Powered by plate tectonics, the Earth’s crust and continents are constantly changing, shifting, losing and adding material through a host of geological processes. It’s amazing, though, that scientists are able to piece together the geological past and, in doing so, enrich our history and pinpoint our place in nature — one species that’s been alive for only 0.0022 percent of the time this planet has been around.

One of the most groundbreaking geological findings involves an ancient slab of sea floor beneath the East Mediterranean Sea which Roi Granot, a professor at the Ben Gurion University in Israel, says is up to 340 million years old. It’s the oldest yet and by far, being 70% older than any other known oceanic crust ever discovered. Around that time, the world’s landmasses were coming together to form the supercontinent Pangea.

pangaea oceanic crust

Credit: Wikimedia Commons

Granot and colleagues towed magnetic sensing equipment on a special vessel which they used to survey the Mediterranean Sea for geophysical anomalies between October 2012 through October 2014. In these two long years, the researchers gathered 7,000 km worth of marine magnetic profiles across the Herodotus and Levant Basins, eastern Mediterranean.

The researchers were specifically on the watch out for oceanic crust since they knew they might find something beneath the thick layers of sediments which could be eight kilometers thick. Obviously, you can’t drill or ‘fish’ for rocks. Instead, modern geophysical methods enable researchers to use magnetic anomalies as proxies to build snapshots as if the oceanic crust was laid bare in front of them.

These magnetic anomalies are the signatures of magnetic minerals in rocks trapped in the oceanic crust, formed undersea by volcanic ridges. As the magma cools, the newly formed minerals in the rocks become magnetized and aligned with the direction of Earth’s magnetic field.

“Changes in the magnetic field’s orientation over time are recorded in the ocean floors, creating a unique barcode that provides a time stamp for crust formation,” Dr. Granot says. “The results shed new light on the tectonic architecture and evolution of this region and have important implications on various geodynamic processes.”

Eventually, Granot identified a pattern of magnetic anomalies like magnetic stripes — the hallmark of oceanic crust formed at a mid-ocean ridge. This led him to believe that the ancient crust he and colleagues had just discovered in the Herodotus Basin is 340 million years old. For comparison, all the other oceanic crusts are no older than 200 million because their high density typically pulls them back down in the mantle through subduction zones where they get recycled. What’s more, the team speculates that the slab might have once belonged to the long lost Tethys Ocean — an ocean that existed during much of the Mesozoic Era, before the Indian and Atlantic Oceans appeared during the Cretaceous Period.

“The area is covered by thick sedimentary coverage, making it unclear precisely how old the crust is and whether it is even oceanic at all,” Dr. Granot says. With the new geophysical data, we could make a big step forward in our geological understanding of the area.”

If Granot’s assumption about the Herodotus crust and the Tethys Ocean is correct, then Tethys could have formed at least 50 million years earlier than thought.

Ref: Palaeozoic oceanic crust preserved beneath the eastern Mediterranean, Nature Geoscience, nature.com/articles/doi:10.1038/ngeo2784

 

Deep lying bacteria found, reproduce only once in 10.000 years

A surprisingly diverse range of life forms exists deep in the oceanic crust, but they live at an extremely slow pace. Long lived bacteria, which reproduce only once in 10.000 years, have been found in rocks 2.5km below the ocean floor, rocks which are 100 million years old. Viruses and fungi have also been found in the same conditions.

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Aside from its intrinsic value, the discovery raises some significant questions, regarding how life can persist under such extreme conditions of temperature, pressure, and apparent lack of nutrients. Scientists from the Integrated Ocean Drilling Program have announced the findings at the Goldschmidt conference, in Florence, Italy.

It’s not the first time the Integrated Ocean Drilling Program has come up with exciting results – in 2012, they set a new record for scientific ocean drilling, and in March this year, they reported the first case of bacteria living in the oceanic crust. Now, Fumio Inagaki of the Japan Agency for Marine-Earth Science and Technology explained that the microbes exist in very low concentrations – around 1000 in every teaspoon of sample, compared to the billions or trillions which you would get in the same amount of surface material.

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Just as interesting, they found that not only do viruses also exist at these depths, but they significantly outnumber the bacteria – 10 to 1, and even more as you go deeper. This offers some important information on what we know on viruses.

“We’re pushing the boundaries of what we understand about how viruses cycle on Earth elsewhere, by studying them in the deep biosphere” Dr Beth Orcutt of Bigelow Laboratory for Ocean Sciences in Maine, US, explained.

Alive… or just undead?

The characteristics of these specimens make researchers question if they even are alive.

“One of the biggest mysteries of life below the sea floor is that although there are microbes down there it’s really hard to understand how they have enough energy to live and how incredibly slowly they are growing.

“The deeper we look, the deeper we are still finding cells, and the discussion now is where is the limit? Is it going to be depth, is it going to be temperature? Where is the limit from there being life to there being no life?”

They are reproducing so rarely that it’s very much unlike anything science has encountered so far.

“The other question we have is that even though we are finding cells, is it really true to call it alive when it’s doubling every thousands of years? It’s almost like a zombie state,” Dr Orcutt commented.

A reproductive cycle of 10.000 years is indeed a few magnitudes of order higher than anything we know, but these microbial communities which inhabit the deep earth are alive by every definition, and they may very well change what we think about life itself.

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.

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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.

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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

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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.