Beginning of Plate Tectonics Was More Recent and More Gradual Than Expected Based on Northwest Australian Rocks

      

      Researchers from Cologne University present important new constraints showing that plate tectonics started relatively slowly, although the early earth's interior was much hotter.

       For this research, reported in the January 12, 2021 Proceedings of National Academy of Sciences, geologists and geophysicists led by Dr. Jonas Tusch  investigated up to 3.5 billion year old igneous rocks from northwest Australia that cover 800 million years of earth's early history.

 

      The analysis of these rock successions reveals that the oldest samples exhibit small anomalies in the isotope abundances of the element tungsten (W) that progressively diminish with time. 

     The origin of these anomalies, namely the relative abundance of 182W, relates to ancient heterogeneities in the terrestrial mantle that must have formed immediately after formation of the earth more than 4.5 billion years ago. The novel tool of high-precision 182W isotope measurements to rocks from the Pilbara Craton in Australia, that span an age range from 3.5 billion years to 2.7 billion years, was used in this study.

      The preservation of these 182W anomalies in the igneous rocks from northwest Australia demonstrate that pristine mantle reservoirs from the beginning of our planet were conserved over timescales exceeding more than one billion years during the Hadean time period.

      This finding is very surprising, because higher mantle temperatures in the early earth suggest that mantle convection was more extensive and much faster than today. Interestingly, the observed 182W anomalies start to diminish at around 3 billion years ago, within a geological era that is assumed to mark the beginning of modern plate tectonics. 

     The onset of modern plate tectonics, involving subduction processes and mountain uplift, has been shown to be a key event triggering the emergence of large continental masses and an oxygen-rich atmosphere, all of which set the stage for the origin of more complex life. This artist conception of earth during the Hadean time period (which predates "modern" plate tectonics).

Here's to our oxygen-rich atmosphere of 2021. Breathe deep and sense those plates moving!

Steph [aka WW (Tungsten Tungsten;-))]

Introducing Bruno!

      This is a good day to introduce Bruno, a Denver Dumb Friends League pup, rescued from the same place as Maizie, the night before election day.

     Bruno joined foster pup, Millie, and the two were hysterical romping, spooning, and whispering to each other. It made election night lots more fun. They had a blast together until Millie went to her furever home with a veteran and his parrot the day before Thanksgiving.

     Bruno is 4 years old and was surrendered with his 7 year old mom. He needed someone to pal around with for awhile. And in return, Bruno taught Millie, also 4, the art of house training. A win-win for everyone!

     I did consider adopting both of them but when this vet held Millie, close to tears of joy in his eyes, I knew Millie needed to be with him. He lost his dog at the same time that Maizie died. We are planning playdates so they will be together again.

      

       We are already looking forward to a Christmastime visit to the Great Sand Dunes to roam the dunes and let some of Maizie's ashes blow in that beautiful wind. I sure miss Maizie but Bruno's curious, slightly shy, and funny nature is helping me with grief.

         We'll get back to science topics next month, after the last 3 weeks of school. In the meantime, I would love to hear your dog tales, cat tales, gerbil tales, parrot tales...

With dogged determination,

Steph and Bruno

The Amazing Maizie 14 years, PEOTS 7 years

      On this 7-year anniversary of Partial Ellipsis of the Sun and 14th-year anniversary of Maizie’s birth (in October), I am writing about Maizie, canine extraordinaire.

     Maizie May was my beloved, fun, and happy companion for 12.5 years. I went to the Denver Dumb Friends League with my friend, Mike, on April 2, 2008. "Pucker" was released from the lost animals hold for exactly 1 minute when we found each other. I ran down the hall to the Adoption Desk saying "She's the one! She's the one!" And so the newly-named Maizie came home the next day to live with my daughter, Zoë, and me. Here she is on that day.

      This girl loved a good road trip. We took more than a dozen  trips to the Great Sand Dunes, one of her two favorite places. Kunming Park was the other favorite. 

      We trekked to Arches National Park, the Paint Mines in Calhoun, to Crystal Bridges Art Museum in Arkansas, to Minnesota for Zoe’s drop-off and graduation from college. We took so many trips to Silver Plume, Palisade, and all over the Colorado, Utah, and Wyoming mountains.

          She liked to rest on my left knee as I drove, soaking up the sunshine and scanning the scenery for elk, deer, and other furry friends. She slept on my left shoulder at night.

            Maizie died in my arms September 21, 2020 at 4:40 p.m. She was bathed in heliotrope-magenta light as she crossed over the Rainbow Bridge. I held her body for over an hour and felt her comforting me.

      During the ten months she fought lymphoma with chemotherapy and her oncologist’s help, we had some awesome adventures, including a trip to San Luis Park and the Great Sand Dunes in April, just before they closed the gates:

https://youtu.be/bhnOENk2QDk

Maizie was spunky, calm, sweet, and adventurous and up for new treks up until the day she died. The growths on her neck returned and even large doses of lomustine could not stop them. She was still so Maizie right up to the end when breathing was difficult. 

           I miss her every minute and talk to her all the time. She brought me such joy. Grief is so non-linear. I find sad tears, happy smiles, weird firsts (moving her water bowls) commingle. 

      I saw her in the full moon Thursday night. She was smiling broadly, telling me she is always in my heart and how much she loved our adventures. 

       

     Here’s to Maizie, the most faithful, loving, sweet dog ever.

     Thanks for coming on this mountain and park ride with me.

Happy trails, Maizie,

Steph

            

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?
Steph

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,

Steph

P.S. Begone, M a r c h, oh longest of months this year.

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 dune 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.

Steph