We may find deep-sea microbes resting in tombs they built themselves

Featured Image: Alvin – a submersible Human Occupancy Vehicle (HOV) designed to allow data collection at depths up to 6,500 m below the ocean surface. Featured image courtesy of John Magyar, Caltech.

Paper: Microbially induced precipitation of silica by anaerobic methane-oxidizing consortia and implications for microbial fossil preservation

Authors: Daniela Osorio-Rodriguez, Kyle S. Metcalfe, Shawn E. McGlynn, Hang Yu, Anne E. Dekas, Mark Ellisman, Tom Deerinck, Ludmilla Aristilde, John P. Grotzinger, and Victoria J. Orphan

Maybe one weekend in your life, you found yourself piling into an SUV at 6 AM with seven other students, intermittently registering the drone of an overenthusiastic geology professor whose course you took to fulfill a degree requirement. If so, in that vehicle, the proclamation that “the present is the key to the past” was certainly uttered. A recent study conducted by Daniela Osorio-Rodriguez and collaborators epitomizes the power of those words.

You likely have heard a great deal about carbon dioxide (CO2) and its effect on the climate as a greenhouse gas in the past few years. The second most commonly discussed greenhouse gas is methane (CH4), largely because it has ~28x the warming potential of CO2 over a 100-year timescale. For this reason, scientists have been interested in microorganisms that convert CH4 to CO2 as their means of obtaining energy to live – a process referred to as methane oxidation. These organisms play an important role in preventing the accumulation of methane in the atmosphere. In most soils, including the grass outside your home, methane oxidation occurs with the help of oxygen (aerobically). However, in sediments at the bottom of the ocean, oxygen is exhausted and methane-oxidizing bacteria must carry out this process anaerobically.

For over two decades, microbial ecologists have been studying the anaerobic oxidation of methane (AOM) by a syntrophic consortium of methanotrophic archaea and sulfate-reducing bacteria (ANME-SRB) living as aggregates around ocean floor methane seeps. The AOM leaves a chemical signature in the limestone rocks that the microbes live in. This signature has been used to identify ancient methane seeps throughout the geologic past. At these sites, geologists have searched for fossilized evidence of ANME-SRB aggregates in rocks. You can imagine this search being like looking for dinosaur bones, except the fossils you are looking for are microscopic.

For decades, geologists have collected rocks from ancient methane seeps all over the world and searched for ANME-SRB under the microscope. Despite significant effort, geologists have yet to observe fossilized aggregates of ANME-SRB. This is the mystery that Osorio-Rodriguez and collaborators are helping resolve in their recent paper. While they did not find fossils of ancient aggregates, they have found what we should be looking for! They observed microbially enhanced precipitation of silica (chemically similar to everyday glass) on the exterior of aggregates in lab cultures, carbonate rocks, and methane-rich sediments. By changing the water chemistry around them, the microbes cause silica to precipitate from the solution in the same way mineral coatings precipitate around a faucet if the water is ‘hard’. To determine the co-occurrence of ANME-SRB aggregates and silica, the authors interrogated laboratory cultures of ANME-SRB with a number of techniques.

  1. Fluorescence in situ hybridization (FISH) – This technique attaches a fluorescent molecule to a target DNA sequence, so that cells expressing this target DNA glow. Using target DNA for both ANME and SRB, the researchers can identify ANME-SRB aggregates as clusters of pink (ANME) and blue SRB) cells.
  2. Scanning Electron Microscopy (SEM) – This technique produces highly magnified images, allowing the researchers to identify ∼230 nanometer-sized amorphous silica spheres (small glass beads nearly 500x smaller than the thickness of a piece of paper) adjacent to the cell aggregates.
  3. Energy dispersive X-ray spectroscopy (EDS) – This technique allows scientists to make maps of elements (ex. silicon, carbon, etc.) around an aggregate while it is being photographed on the SEM.

Not only did the researchers observe the repeated precipitation of silica around the aggregates, by studying the chemistry of the artificial seawater, they could confirm that the silica could not be precipitating abiotically (without the presence of microbes) in their experiments. This allowed them to confirm that the cellular activity must play a role in the silica precipitation they observed. Also, they found that the silica precipitated near the aggregates is chemically different (containing less Mg, Al, and Fe) from other silicate minerals found at methane seeps.

Like all groundbreaking research, this study has raised new questions that have yet to be answered. While the authors are confident that the microbial activity is inducing the silica precipitation, how the microbes are doing this is still unknown. The eventual explanation will involve homing in on biochemical processes occurring in either ANME clusters, SRB clusters, or at the interface between the two that locally changed the water chemistry such that silica preservation is favorable. All that means is there is more exciting science be carried out.

Importantly, this research on modern aggregates has armed geologists with a new target in the search to identify fossilized consortia in the geologic past.

We may find deep-sea microbes resting in tombs they built themselves © 2024 by Joshua Anadu is licensed under CC BY-SA 4.0 

Unlocking Magma’s Mysteries

Understanding magma’s behavior may predict eruptions and reveal historic landscapes

By: Ellen Beshuk

Sometimes magma calmly flows; other times, it explodes. Ph.D. candidate Ivana Torres-Ewert is figuring out why with her magma-making machine at the University of Missouri-Kansas City (UMKC). Her discoveries could help people know where to go when a volcano explodes and provide a foundation for further volcanic research.

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Microscopic Miners: How invisible forces create tropical caves

Featured Image: Scientist Ceth Parker moving through a passageway within an iron formation cave.  Photo courtesy of the University of Akron.

Paper: Enhanced terrestrial Fe(II) mobilization identified through a novel mechanism of microbially driven cave formation in Fe(III)-rich rocks

Authors: Ceth W. Parker, John M. Senko, Augusto S. Auler, Ira D. Sasowsky, Frederik Schulz, Tanja Woyke, Hazel A. Barton

Consider this: microscopic creatures literally moving tons of rock before your very eyes. It seems too fantastical, but maybe not if you’re in the Brazilian tropics. In new work, scientists have detailed these stealthy and microscopic processes, naming a new cave generation pathway called exothenic biospeleogenesis, or “behind-wall life-created” caves.

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How plants left a mark on history

Featuring image: Plants slowly eroding limestone. Picture from Jon Sullivan, public domain (C0).

Paper: Composition of continental crust altered by the emergence of land plants

Authors: C. J. Spencer, N. S. Davies, T. M. Gernon, X. Wang, W. J. McMahon, T. R. I. Morrell, T. Hincks, P. K. Pufahl, A. Brasier, M. Seraine and G.-M. Lu 

In the winter of 1990, the first Voyager spacecraft looked over its shoulder and snapped an iconic photo of Earth as a ‘pale blue dot’ in the vast cosmos. But when you look at it from Space, there is another very important colour: green. Plants cover a major portion of the landmasses. Besides bringing their bright chlorophyll colour to the continents, new research by Spencer and co-authors finds that plants have also slowly changed the composition of the Earth’s crust over hundreds of millions of years.

In a recent study, Spencer and co-workers were able to connect the development of land plants to changes in the geochemical composition of crustal rocks through the effects that plants had on landscapes, weathering, and sediments. Land plants arose during the early Ordovician period, about 440 million years ago, and today they cover approximately 84% of Earth’s landmasses. After they spread all over the continents, plants started to heavily influence the sedimentary cycles between continents and oceans.

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Silver Doesn’t Grow on Trees: The Quest for the Ores that Formed Roman Coinage

Featured image: A silver Roman Denarius, featuring the likeness of emperor Marcus Aurelius. CC BY-SA 3.0 via Wikimedia Commons

Paper: Silver isotope and volatile trace element systematics in galena samples from the Iberian Peninsula and the quest for silver sources of Roman coinage

Authors: Jean Milot; Janne Blichert-Toft; Mariano Ayarzagüena Sanz; Chloé Malod-Dognin; Philippe Télouk; Francis Albarède

The Roman Empire was a superpower thousands of years ago, and with great power comes great (fiscal) responsibilities, including minting the money. To mint silver coins, the Romans needed vast amounts of silver, which historians and archeologists believe originated in the Iberian Peninsula, or present-day Spain and Portugal. However, the geologic origin of that silver is unknown as the depleted mines were abandoned long ago.

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What caused the end-Triassic Mass Extinction in the Oceans?

Feature Image: Outcrop of volcanic rock associated with the Central Atlantic Magmatic Province. This Large Igneous Province has a strong correlation to the onset of a mass extinction ~200 million years ago, however, an exact mechanism for the extinction has been difficult to determine. CC BY-SA 4.0, via Wikimedia Commons

Paper: Two-pronged kill mechanism at the end-Triassic mass extinction

Authors: Calum P. Fox; Jessica H. Whiteside; Paul E. Olsen; Xingquian Cui; Roger E. Summons; Kliti Grice

Journal: Geology

A recent study by Calum Fox and colleagues sheds light on what caused one of the “big five” mass extinctions on Earth since complex life emerged ~540 million years ago. They found that repeated pulses of volcanic activity were responsible for the extinction in two main ways: ocean poisoning caused by gaseous hydrogen sulfide (H2S) rising through the water column (known as euxinia) and ocean acidification.

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Metal-Eating Microbes Who Breathe Methane

Featured Image: Murky pond in Alaska with “rusty” iron-filled sediments. Image courtesy Jessica Buser. Used with permission.

Paper:  Sulfate- and iron-dependent anaerobic methane oxidation occurring side-by-side in freshwater lake sediment

Authors: Alina Mostovaya, Michael Wind-Hansen, Paul Rousteau, Laura A. Bristow, Bo Thamdrup

The table has been set and the food is all prepared. But this is no ordinary dinner party, it’s a microbe party! The guests sit down and proceed to dig into the main course; sulfur, rusty iron, and methane. Curiously, the guests are feeding each other, not themselves! This image seems pretty weird to us humans, but it’s a delight to these microbes. This collaborative method of eating occurs in pond and lake mud all around the world. In a new study, Mostovaya and colleagues describe one such feast in Danish Lake Ørn, that is not only collaborative but may mitigate climate change.

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Buried treasure in the oceans: chemistry of small deep-sea crystals hints at past carbon cycling

Featured image: Crystals of the mineral barite from the deep ocean (Adapted from Kastner (1999)). These crystals precipitated in ocean sediments and are about 9 million years old, similar in age to some of the barite samples from the study discussed here.

Paper: A 35-million-year record of seawater stable Sr isotopes reveals a fluctuating global carbon cycle

Authors: Adina Paytan, Elizabeth M. Griffith, Anton Eisenhauer, Mathis P. Hain, Klaus Wallmann, Andrew Ridgwell

What do ancient ocean sediments and the walls around x-ray machines have in common? One possible answer? Sometimes the mineral barite is an important part of both!  Barite (or barium sulfate) is able to block gamma and x-ray emissions, and therefore is sometimes used in high-density concrete in hospitals and laboratories. In the deep ocean, tiny crystals of barite naturally accumulate on the seafloor over time, particularly in regions ideal for this mineral formation where many decaying remains of organisms sink to the seafloor. The chemistry of this barite can give scientists clues into Earth’s past, which is what Adina Paytan and her colleagues did in this study.

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Life on Mars: a non-traditional source for warmer waters

Hydrothermal vent on the right spewing water into a river on the left. Background has trees and sky. From Yellowstone National Park.

Article: Amagmatic hydrothermal systems on Mars from radiogenic heat

Authors: L. Ojha, S. Karunatillake, S. Karimi, and J. Buffo

Many people are familiar with Yellowstone National Park’s famous geyser, Old Faithful – but did you know that the heat fueling Old Faithful’s eruptions are from magma chambers that warm up underground fluids until they shoot out of the ground? Hydrothermal systems like this are found in other places, too, and can be fueled by different kinds of heat sources. In fact, scientists at Rutgers University have recently identified one such heat source – the heat generated by radioactive decay from certain chemical elements – that could help answer questions about whether liquid water, a critical component for life as we know it, could exist on Mars.

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Tiny Crystals, Big Story: Time capsules from the Early Mars

Featured Image: Zircon grain under the Scanning Electron Microscope (SEM). Image used with permission from Wikipedia (Emmanuel Roquette).

Article: The internal structure and geodynamics of Mars inferred from a 4.2-Gyr zircon record.

Authors: Maria M. Costa, Ninna K. Jensen, Laura C. Bouvier, James N. Connelly, Takashi Mikouchi, Matthew S. A. Horstwood, Jussi-Petteri Suuronen, Frédéric Moynier, Zhengbin Deng, Arnaud Agranier, Laure A. J. Martin, Tim E. Johnson, Alexander A. Nemchin, and Martin Bizzarro

While sitting in Geology 101 studying the geological time scale, most of us have gone through this experience where we imagined ourselves going back in time; visualizing mammoths passing by, dinosaurs hunting and fighting. But all these pictures start to become hazy and unclear when we reach close to 4 billion years. It is the time for which we have no rock records, and this is where zircons or what I would like to call “tiny survivors” comes in.

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