Total Pageviews

Saturday, May 2, 2020

Rudists, Nudists, and Buddhists

     Although we have already discussed rudist (not rudest) clams here at PEOTS, new research about these reef builders of the Cretaceous was just published in February, 2020, warranting another look. Plus, I like the "Rudists, Nudists, and Buddhists" title. Rudists colonizing in zen-like seas? Count us in. 

        The earth turned faster at the end of the Cretaceous than it does today, rotating 372 times a year, compared to the current 365 1/4, according to a new study of fossil rudist shells. The research also shows a day lasted only 23.5 hours, according to the new study in American Geophysical Union's journal Paleoceanography and Paleoclimatology.

     The ancient mollusk, from an extinct and quite diverse group known as rudist clams, grew fast, laying down daily growth rings. The new study used lasers to sample minute slices of shell and count the growth rings with great accuracy. The growth rings allowed the researchers to determine the number of days in a year and more accurately calculate the length of a day 70 million years ago. The new measurement informs models of how the Moon formed and how close to Earth it has been over the 4.5-billion-year history of the Earth-Moon gravitational dance.

     The high resolution obtained in the new study combined with the fast growth rate of the ancient bivalves revealed unprecedented detail about how the animal lived and the water conditions it grew in, down to a fraction of a day.
     "We have about four to five datapoints per day, and this is something that you almost never get in geological history. We can basically look at a day 70 million years ago. It's pretty amazing," said Dr.  Niels de Winter, an analytical geochemist at Vrije Universiteit Brussel and the lead author of the new study.

     Climate reconstructions of the deep past typically describe long term changes that occur on the scale of tens of thousands of years. Studies like this one give a glimpse of change on the timescale of living things and have the potential to bridge the gap between climate and weather models.
     Chemical analysis of the shell indicates ocean temperatures were warmer in the Late Cretaceous than previously appreciated, reaching 40 degrees Celsius (104 degrees Fahrenheit) in summer and exceeding 30 degrees Celsius (86 degrees Fahrenheit) in winter. The summer high temperatures likely approached the physiological limits for mollusks, de Winter said.

     "The high fidelity of this data-set has allowed the authors to draw two particularly interesting inferences that help to sharpen our understanding of both Cretaceous astrochronology and rudist palaeobiology," said Dr. Peter Skelton, a retired paleobiologist at the Open University and a rudist expert unaffiliated with the new study.
    The new study analyzed a single individual that lived for over nine years in a shallow seabed in the tropics -- a location which is now, 70-million-years later, dry land in the mountains of Oman.
     "Torreites sanchezi mollusks look like tall pint glasses with lids shaped like bear claw pastries. The ancient mollusks had two shells, or valves, that met in a hinge, like asymmetrical clams, and grew in dense reefs, like modern oysters. They thrived in water several degrees warmer worldwide than modern oceans."
     In the late Cretaceous, rudists like T. sanchezi dominated the reef-building niche in tropical waters around the world, filling the role held by corals today. They disappeared in the same event that killed the non-avian dinosaurs 66 million years ago.

     "Rudists are quite special bivalves. There's nothing like them living today," de Winter said. "In the late Cretaceous especially, most of the reef builders are these bivalves. So they really took on the ecosystem building role that the corals have today."
     The new method focused a laser on small bits of shell, making holes 10 micrometers in diameter, or about as wide as a red blood cell. Trace elements in these tiny samples reveal information about the temperature and chemistry of the water at the time the shell formed. The analysis provided accurate measurements of the width and number of daily growth rings as well as seasonal patterns. The researchers used seasonal variations in the fossilized shell to identify years.

     The new study found the composition of the shell changed more over the course of a day than over seasons, or with the cycles of ocean tides. The fine-scale resolution of the daily layers shows the shell grew much faster during the day than at night.
     "This bivalve had a very strong dependence on this daily cycle, which suggests that it had photosymbionts," de Winter said. "You have the day-night rhythm of the light being recorded in the shell."

     This result suggests daylight was more important to the lifestyle of the ancient mollusk than might be expected if it fed itself primarily by filtering food from the water, like modern day clams and oysters, according to the authors. De Winter said the mollusks likely had a relationship with an indwelling symbiotic species that fed on sunlight, similar to living giant clams, which harbor symbiotic algae.
     "Until now, all published arguments for photosymbiosis in rudists have been essentially speculative, based on merely suggestive morphological traits, and in some cases were demonstrably erroneous. This paper is the first to provide convincing evidence in favor of the hypothesis," Skelton said, but cautioned that the new study's conclusion was specific to Torreites and could not be generalized to other rudists.

     De Winter's careful count of the number of daily layers found 372 for each yearly interval. This was not a surprise, because scientists know days were shorter in the past. The result is, however, the most accurate now available for the late Cretaceous, and has a surprising application to modeling the evolution of the earth-moon system.
     The length of a year has been constant over earth's history, because earth's orbit around the sun does not change. But the number of days within a year has been shortening over time because days have been growing longer. The length of a day has been growing steadily longer as friction from ocean tides, caused by the moon's gravity, slows earth's rotation.

    The pull of the tides accelerates the moon a little in its orbit, so as earth spin slows, the moon moves farther away. The moon is pulling away from earth at 3.82 centimeters (1.5 inches) per year. Precise laser measurements of distance to the moon from earth have demonstrated this increasing distance since the Apollo space program left helpful reflectors on the moon's surface.
     But scientists conclude the moon could not have been receding at this rate throughout its history, because projecting its progress linearly back in time would put the moon inside the earth only 1.4 billion years ago. Scientists know from other evidence that the Moon has been with us much longer, most likely coalescing in the wake of a massive collision early in Earth's history, over 4.5 billion years ago. So the Moon's rate of retreat has changed over time, and information from the past, like a year in the life of an ancient clam, helps researchers reconstruct that history and model of the formation of the moon.

       Rudists' growth patterns and rates provide great data for models from the Cretaceous.

Have you encountered any rudists in your fossil meanderings around the earth?

Tuesday, March 31, 2020

Diatoms and Diatomaceous Earth: Beer Filtration for What Ales You

      Diatomite is a generally light-colored sedimentary rock that is  composed mostly of the siliceous skeletons of diatoms. It is an extremely porous rock with a fine particle size and a low specific gravity. These properties make it useful as a filter media, especially for beer and wine. It is also used as an absorbent, and as a lightweight filler for paint and plastics. When diatomite is crushed into a very fine powder, it is called diatomaceous earth.

      Diatoms are members of a large, diverse group of algae that drift in the waters of both oceans and lakes. A few types of diatoms live on the bottom of these water bodies and in soils. Most diatoms are microscopic, although a few species are up to two (2) mm in length. As a group, diatoms are unique because they are single-celled organisms that produce an external cell wall composed of silica, called a frustule. These frustules are very thin and have a delicate structure.

      Most diatoms are photosynthetic and live in water less than thirty (30) feet deep, where sunlight can penetrate. Diatoms are prolific and are responsible for producing nearly half of the organic mass in the world’s oceans. Their abundance and tiny size places them at the base of the marine food chain. We have discussed the strength and Fibonacci ordering of diatoms before here at PEOTS.

     After diatoms die ("die, atoms, die!"-- sorry, I couldn't resist) their siliceous frustules sink. In some areas, the frustules are not incorporated into the bottom sediment because they dissolve as they sink or dissolve while on the sediment surface. If the sediment is composed of over 30% diatom frustules by weight, it is called diatomaceous ooze or siliceous ooze.

      Of course, all this ooze discussion leads to a talk of diatomaceous ooze filtering your booze. Freshwater ooze or earth must be used unless you like your booze salty (yuck for me!).    Diatomite from saltwater sources can contain salts that can produce objectionable or toxic effects. Although some beer crafters are, indeed, using salt in the brewing process. Enjoy the beer, skip the pretzels? Have a little diatomaceous ooze with your booze? Woe is mead?


     The four main uses of diatomite in the United States during 2019 were filtration (50%), light aggregate (30%), fillers (15%), and absorbents (5%).

      Diatomaceous earth is used as a lightweight, inert filler in some manufactured products. It is added to paint as a whitening agent and extender. Diatomite is added to plastics as a lightweight filler. 

     If dry diatomaceous earth is placed on a liquid spill, it can absorb and hold an amount of liquid equivalent to its own weight. This absorption facilitates containment, cleanup, and removal. Capillary action of liquids into diatomaceous earth is enhanced by its small particle size, high surface area, and its high porosity.

       These same properties make diatomaceous earth able to absorb skin oils when used in cosmetics and facial masks. Diatomaceous earth is an absorbent ingredient of some kitty litters. It is also used as a soil treatment to absorb and hold water.

     Diatomaceous earth is used as a mild abrasive in some toothpastes, facial scrubs, and metal polishes. Its silica particles are small, friable, have a high surface area, and are angular in shape. These are properties that help it perform well as a mild abrasive.

     Diatomaceous earth is used as a growing medium in hydroponic gardens. It is inert, holds water, and has a porosity that allows the soil to breathe. To help grain and other seeds from sticking together and remain dry, they are dusted with diatomaceous earth.

     The cost of diatomite depends on its quality, how it will be used, and the preparation effort that has been invested by the supplier. The cost of diatomite straight from the mine without processing for use in concrete starts at about $7/ton. Diatomite from high-grade deposits that has been crushed, sized, and sieved for use in cosmetics, art supplies, & DNA extraction markets can cost more than $400/ton.

     The extraordinary intricacy of diatoms in Scanning Electron Micrographs shown throughout this post is astounding. Do you have a favorite?
Hoping you are all well in this weirdest of times,
P.S. Begone, M a r c h, oh longest of months this year.

Wednesday, February 5, 2020

Many Grains of Truth: Sand Dunes "Communicating" with Each Other

Although they are an inanimate  collection of objects, sand dunes can 'communicate' with each other. Researchers from the UniversitCambridge have discovered that as they shift, sand dunes interact with and repel their sand dune neighbors downstream.

      Although they are an inanimate  collection of objects, sand dunes can 'communicate' with each other. Researchers from the University of Cambridge have discovered that as they shift, sand dunes interact with and repel their sand dune neighbors downstream.

         [Another sand dunes post?! Yes, it's true that Dunes hold a special place in my heart and in the heart of Maizie. On Sunday, on a blue-sky 75 degree F day, Maizie dug happily in a big sand pit on our walk as I thought "We need to get back to the Great Sand Dunes (above) in southern Colorado." Of course, today is not that day as it was -5 degrees F this morning. An 80 degree F swing? Yes, indeed. See above photo from the National Park Service.]

     "Using an experimental dune 'racetrack', the team observed that two identical dunes start out close together, but over time they get further and further apart. This interaction is controlled by turbulent swirls from the upstream dune, which push the downstream dune away. The results, reported in the journal Physical Review Letters, are key for the study of long-term dune migration, which threatens shipping channels, increases desertification, and can bury infrastructure such as highways.
When a pile of sand is exposed to wind or water flow, it forms a dune shape and starts moving downstream with the flow. Sand dunes, whether in deserts, on river bottoms or sea beds, rarely occur in isolation and instead usually appear in large groups, forming striking patterns known as dune fields or corridors."

     "Active sand dunes migrate. Generally speaking, the speed of a dune is inverse to its size: smaller dunes move faster and larger dunes move slower. What hasn't been understood is if and how dunes within a field interact with each other."

     "There are different theories on dune interaction: one is that dunes of different sizes will collide, and keep colliding, until they form one giant dune, although this phenomenon has not yet been observed in nature," said Dr. Karol Bacik of Cambridge's Department of Applied Mathematics and Theoretical Physics, and the paper's first author. "Another theory is that dunes might collide and exchange mass, sort of like billiard balls bouncing off one another, until they are the same size and move at the same speed, but we need to validate these theories experimentally."

     Now, Dr. Bacik and his Cambridge colleagues have shown results that question these explanations. "We've discovered physics that hasn't been part of the model before," said Dr. Nathalie Vriend, who led the research.

     "Most of the work in modelling the behavior of sand dunes is done numerically, but Dr. Vriend and the members of her lab designed and constructed a unique experimental facility which enables them to observe their long-term behaviour. Water-filled flumes are common tools for studying the movement of sand dunes in a lab setting, but the dunes can only be observed until they reach the end of the tank. Instead, the Cambridge researchers have built a circular flume so that the dunes can be observed for hours as the flume rotates, while high-speed cameras allow them to track the flow of individual particles in the dunes."

     Dr. Bacik hadn't originally meant to study the interaction between two dunes: "Originally, I put multiple dunes in the tank just to speed up data collection, but we didn't expect to see how they started to interact with each other," he said.

     "The two dunes started with the same volume and in the same shape. As the flow began to move across the two dunes, they started moving. "Since we know that the speed of a dune is related to its height, we expected that the two dunes would move at the same speed," said Vriend, who is based at the BP Institute for Multiphase Flow. "However, this is not what we observed."

     Initially, the front dune moved faster than the back dune, but as the experiment continued, the front dune began to slow down, until the two dunes were moving at almost the same speed.

     Crucially, the pattern of flow across the two dunes was observed to be different: the flow is deflected by the front dune, generating 'swirls' on the back dune and pushing it away. "The front dune generates the turbulence pattern which we see on the back dune," said Vriend. "The flow structure behind the front dune is like a wake behind a boat, and affects the properties of the next dune."

     As the experiment continued, the dunes got further and further apart, until they form an equilibrium on opposite sides of the circular flume, remaining 180 degrees apart.

     The next step for the research is to find quantitative evidence of large-scale and complex  migration in deserts, using observations and satellite images. By tracking clusters of dunes over long periods, we can observe whether measures to divert the migration of dunes are effective or not.

Here's hoping flumes don't look leave you flummoxed.


Wednesday, January 8, 2020

Trash Talking Early: Plastic "Continents" of Trash

     Plastic "continents" are not static. Based on the oceanic circulation modelling work conducted in the Pacific, the Institute de Recherche et Developpement (IRD) and the National Council for Scientific Rearch (CNRS) researchers have recently shown that there are exit currents for these areas of the sea where these piles of waste build up. This means that they are not caught in a never-ending whirlpool in the middle of the ocean, as had been previously thought. Although inappropriate given the actual estimated concentrations, this term highlights the awareness of the impact of human activity on the oceans.

.    Due to the winds on the surface of the oceans and the rotation of the earth (via the Coriolis force), huge vortexes, called "oceanic gyres," are formed in each of the five major basins: North and South Pacific, North and South Atlantic, and the Indian Ocean. These huge whirlpools slowly gather in their wake all the plastic objects and waste floating on the surface of the water, accumulating year after year.


      This pollution is now recognized as a global problem, representing a threat to marine biodiversity. In particular, this surface drift acts as a means of transport for the viruses and bacteria that the spread across the oceans.

      Nevertheless, these plastic "continents," as they are incorrectly christened, are not, in fact, static. The IRD and CNRS researchers have recently revealed the existence of "exit doors" leading away from these large surface current convergence zones. The scientists started by studying the oceanic circulation in the Pacific modelled with a much finer spatial resolution than that of the models generally used for this type of study (those typically used for climate research). They simulated the trajectories of several million particles, with currents defined on networks of 1/32° to 1/4° (meaning a range from a few kilometers to thirty or forty kilometers).

      The results obtained highlight currents, several hundred kilometers wide, which escape from the heart of the subtropical gyre and head eastwards instead. In addition to these currents there are physical processes such as the effects of the wind and waves, not taken into account in the models, which can also alter the trajectory and the transit time of the particles and waste.

     In the Pacific, the waste may not necessarily be trapped in the centre of the oceanic gyre and may be removed in the direction of the American coasts. Furthermore, these results are backed up by the work of the IRD's Chilean partners. They have observed an increase in the amount of waste collected on their coastlines.

     More detailed observations, modelling and analyses are needed to gain a better understanding of the ocean surface currents that regulate the slow routing of plastic waste on the surface of the seas and, in the medium-term, implement strategies for collecting and recycling all of this waste.

         I saw first-hand the dumping of all our waste aboard the Research Vessel Eastward in the Mediterranean Sea in 1978. The ship's captain laughed at me when I suggested that continual trash dumping would add up to eventually plug up the oceans. It was so devastating to see those empty cans of Spam floating in the sea.

Trash talking pre-LIV,

Tuesday, October 1, 2019

Machu Picchu: 15th Century Incan Sanctuary Purposely Built on Faults

     "The ancient Incan sanctuary of Machu Picchu constructed in the mid to late 15th century, is considered one of humanity's greatest architectural achievements. Built in a remote Andean setting atop a narrow ridge high above a precipitous river canyon, the site is renowned for its perfect integration with the spectacular landscape. Yet the sanctuary's location has long puzzled scientists -- Why did the Incas build their masterpiece in such an inaccessible place? Research suggests the answer may be related to the geological faults that lie beneath the site."(Wow, ancient ecoarchitects meet ancient Scientific Stephs ;-)).

       "On September 23, 2019, at the Geological Society of America (GSA) Annual meeting Dr. Rualdo Menegat, a geologist at Brazil's Federal University of Rio Grande do Sul,  presented the results of a detailed geoarchaeological analysis that suggests the Incas intentionally built Machu Picchu -- as well as some of their cities -- in locations where tectonic faults meet. "Machu Pichu's location is not a coincidence," says Dr. Menegat. "It would be impossible to build such a site in the high mountains if the substrate was not fractured."

    " Using a combination of satellite imagery and field measurements, Menegat mapped a dense web of intersecting fractures and faults beneath the UNESCO World Heritage Site. His analysis indicates these features vary widely in scale, from tiny fractures visible in individual stones to major, 175-kilometer-long lineaments that control the orientation of some of the region's river valleys."

     "Dr. Menegat found that these faults and fractures occur in several sets, some of which correspond to the major fault zones responsible for uplifting the Central Andes Mountains during the past eight million years. Because some of these faults are oriented northeast-southwest and others trend northwest-southeast, they collectively create an "X" shape where they intersect beneath Machu Picchu. X marks the Machu Picchu spot.

     "Dr. Menegat's mapping suggests that the sanctuary's urban sectors and the surrounding agricultural fields, as well as individual buildings and stairs, are all oriented along the trends of these major faults. "The layout clearly reflects the fracture matrix underlying the site," says Dr. Menegat. Other ancient Incan cities, including Ollantaytambo, Pisac, and Cusco, are also located at the intersection of faults, says Menegat. "Each is precisely the expression of the main directions of the site's geological faults."

     Dr. Menegat's results indicate the underlying fault-and-fracture network is as integral to Machu Picchu's construction as its legendary stonework (as above). This mortar-free masonry features stones so perfectly fitted together that it's impossible to slide a credit card between them. Aside from the obvious aesthetic benefits of this building style, there are engineering advantages. Peru is a seismically unstable country; both Lima and Cusco have been leveled by earthquakes. When an earthquake occurs, the stones in an Inca building are said to “dance;” that is, they bounce through the tremors and then fall back into place. Without this building method, many of the best known buildings at Machu Picchu would have collapsed long ago.

       "As master stoneworkers, the Incas took advantage of the abundant building materials in the fault zone, says Dr. Menegat. "The intense fracturing there predisposed the rocks to breaking along these same planes of weakness, which greatly reduced the energy needed to carve them."

     "In addition to helping shape individual stones, the fault network at Machu Picchu likely offered the Incas other advantages, according to Dr. Menegat. Chief among these was a ready source of water. "The area's tectonic faults channeled meltwater and rainwater straight to the site," he says. Construction of the sanctuary in such a high perch also had the benefit of isolating the site from avalanches and landslides, all-too-common hazards in this alpine environment, Dr. Menegat explains."

     "The faults and fractures underlying Machu Picchu also helped drain the site during the intense rainstorms prevalent in the region. "About two-thirds of the effort to build the sanctuary involved constructing subsurface drainages," says Dr. Menegat. "The preexisting fractures aided this process and help account for its remarkable preservation," he says. "Machu Picchu clearly shows us that the Incan civilization was an built on well-fractured rocks. 

Have any PEOTS folks visited Machu Picchu? How was the experience?

And Happy 6 year anniversary to PEOTS! 

  • We had a Japanese cardiologist stay with us in March 2008. He took the leftover Colorado trail GORP with him to his next stop at MP and sent this image. So it's almost like I've been there...and it looks deserted.