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;-))]

Speaking of Geologic Time Periods Ending in E: Indian Fossils and the Spread of Primate-Like Animals: India's Island Days

      Well-preserved bones of rat-sized creatures excavated in an Indian coal mine may come from close relatives of the first primate-like animals, Iowa, USA, researchers describe.

     A set of two dozen limb fossils, dating to about 54.5 million years ago during the Eocene, raises India’s profile as a possible hotbed of early primate evolution, says biologist Dr. Rachel Dunn. 

      Bones from Vastan coal mine in Gujarat, India’s westernmost state, indicate that these small tree-dwellers resembled the first primates from as early as 65 million years ago, the scientists report in the October 2016 Journal of Human Evolution.

     These discoveries add to previously reported jaws, teeth and limb bones of four ancient primate species found in the same mine. “The Vastan primates probably approximate a common primate ancestor better than any fossils found previously,” says paleontologist and study co-author Dr. Kenneth Rose of Johns Hopkins University.

     The Vastan animals were about the size of living gray mouse lemurs and dwarf lemurs, weighing roughly 150 to 300 grams (about half a pound), the investigators estimate. 

      Most Vastan creatures possessed a basic climbing ability unlike the more specialized builds of members of the two ancient primate groups that gave rise to present-day primates, the researchers say. One of those groups, omomyids, consisted of relatives of tarsiers, monkeys and apes. 

       The other group, adapoids, included relatives of lemurs, lorises and bushbabies. The Indian primates were tree-dwellers but could not leap from branch to branch like lemurs or ascend trees with the slow-but-sure grips of lorises, the new report concludes.

      Vastan primates probably descended from a common ancestor of omomyids and adapoids, the researchers propose. India was a drifting landmass headed north toward a collision with mainland Asia when the Vastan primates were alive. Isolated on a huge chunk of land, the Indian primates evolved relatively slowly, retaining a great number of ancestral skeletal traits, the researchers propose.

      “It’s possible that India played an important role in primate evolution,” says evolutionary anthropologist Dr. Doug Boyer of Duke University. In 2010, a team led by Boyer reported that a roughly 65-million-year-old fossil found in southern India might be a close relative of the common ancestor of primates, tree shrews and flying lemurs (which glide rather than fly and are not true lemurs).

     One possibility is that primates and their close relatives evolved in isolation on the island continent of India between around 65 million and 55 million years ago, Dr. Boyer suggests. Primates then spread around the world once India joined Asia by about 50(?) million years ago.

     This is a controversial idea. An increasing number of scientists suspect primates originated in Asia. Chinese primate fossils dating to 56 million to 55 million years ago are slightly older than the Vastan primates. The Chinese finds show signs of having been omomyids.

      And in at least one respect, Dr. Boyer says, some of the new Vastan fossils may be more specialized than their discoverers claim. Vastan ankle bones, for instance, look enough like those of modern lemurs to raise doubts that the Indian primates were direct descendants of primate precursors.

      Dr. Dunn, however, regards the overall anatomy of the Vastan fossils as “the most direct evidence we have” that ancestors of early primates lacked lemurs’ leaping abilities, contrary to what some researchers have argued. 

Your thoughts? Omo or Ada? Or?
Steph

P.S. My oldest peach tree is loaded with fruit this year! They are just ripening now.

Ganymede Geology: Cup Bearer (of GanyMead?) to the gods

     Before we head to the largest moon of Jupiter, Ganymede, and leave earth's Iceland, this 1 minute and 13 second BBC clip shows the divergent (pulling apart) sea-floor spreading we discussed last Tuesday:

DIVERGENT SEA-FLOOR SPREADING---BBC CLIP

     The three margins described on earth in the concept of plate tectonics: (1) divergent (seen above), (2) convergent (mountain building or orogeny) and (3) transform or strike-slip often associated with earthquakes, may also play a role in the geologic formation of Ganymede.

      Ganymede, discovered by Galileo in January, 1610, has surface area that is greater than half of the surface area of the land mass on earth. The moon was named for Ganymede, the pretty boy who was taken by Zeus to be cup bearer to the gods (Had they been geologists it may well have been mead in those cups :-) ). Ganymede may be seen this month with binoculars:
 

      NASA released a geologic map of Ganymede this week, the first complete geologic map of Jupiter's seventh moon. The "cup bearer" stands out quite well with a blue, dark green, and purple body and green "crater head" on the right side of the first image:

     The geology of Ganymede is especially interesting to geologists because it appears there were times of tectonic movement on this icy moon. These grooves and ridges point to a similar origin to the earth's plate tectonic movement:

    
     In addition, periods of intense crater impacts are seen in the geologic history:

     One of the more interesting features on Ganymede are palimpsests, derived from the word meaning to write over older writing (similar to pentimento overpainting in art). [The word palimpsest is from the Greek for to scrape]:

   
   Similarly, older craters are "overwritten" by younger ones as the older crater margins are eroded through time:

         There were (and are) quiescent times on this frozen, icy moon (quiescently frozen :)) as well.

          There is also evidence for some cryovolcanism (eruption of  volatiles like ice and water, methane, and ammonia from volcanoes) on Ganymede.


      The link to the NASA article contains a 37 second animation so you can also see the "Dark Side of the Moon" (The Pink Floyd song turns 40 next month!):

GANYMEDE GEOLOGIC MAP NASA 2014 

       Looking forward to discussing Ganymede geology, nomenclature, great music, and some planetary geology jokes and puns. Do you have a favorite?

Palimpsestially,(thanks, Lego)

Word Woman (aka Scientific Steph)

Icelandic Plate Tectonics: No Scree-ching Halt: Give It an Inch and It'll Take A Year

     At long last, we are ready for the trip to Iceland now that the Viking Sunstone (optical Iceland spar or calcite) has been found:

Viking Sunstone--Soap-Bar Sized Optical Calcite 

 

     Optical calcite is rhombohedral and refracts light in a way that Norse explorers of 900-1200 A. D. were likely able to locate the sun even after sunset and on cloudy days. In those pre-GPS days, the calcite rhomb was accurate to within 1 degree:

     Optical calcite is found in abundance in the scree of Iceland, though it is now a protected resource since Icelandic tourism has recently blossomed. You may read more about calcite here, but I want to get us to Iceland, the only place on earth (currently) where a mid-oceanic ridge occurs on land:

Calcite Optics

     To repeat, Iceland is the ONLY place on our planet where one may actually witness oceanic crust being created on land. All other parts of the global mid-oceanic ridges are deep beneath the surface of the ocean. These folks are walking between two tectonic plates, the North American plate and the Eurasian plate, in Iceland:

     The theory of plate tectonics describes the large-scale motions of the lithosphere. A good, general overview of the theory may be found here:

 Plate Tectonics Overview

     The divergent boundaries between plates, known as mid-oceanic ridges, are the places where oceanic crust is created. There is a particularly good color, animated graphic in the link below (and shared here) which shows the new basalt (nicknamed MORB for Mid-Oceanic Ridge Basalt) or gabbro being created:

 Mid-Oceanic Ridges

     Oceanic crust is richer in iron and magnesium making it heavier than continental crust, which is richer in lighter silica. The very newest "skin of the earth"  is created at mid-oceanic ridges. As one moves away from the center of the ridge, the oceanic crust is progressively older on mirroring sides of the ridge. Almost all oceanic crust is 200 million years old or younger, fairly young in geologic terms. Then, at the margins with lighter continental crust, the oceanic crust dives beneath the lighter continental crust and is essentially recycled. The major plates and their current movements are shown below:

     In Iceland, one may witness this new "baby earth skin" creation directly. In the land of fire and ice, you can actually touch this brand new earth as the mid-oceanic Atlantic ridge runs right through Iceland:

       The Eurasian and North American plates are moving apart at the rate of about an inch a year. There is no scree-ching halt to the oceanic plate movement due to the convection currents in the earth. The convection is akin to heating up pudding on the stove. The rising hot pudding comes to the surface then plunges back down again as it cools at the surface. 

        To witness new earth being created is, for me, amazing. After seeing the volcanos, ice, spar, and other Icelandic delights, here's that optional side trip to the Lucky Leif bridge in southwestern Iceland. It's a moment to ponder the earth's dynamic nature while straddling the two tectonic plates. Our trip would have been unabridged without it. :-) Enjoy!

        I welcome your comments, insights, and any sparring. 

      Here's to MORB excitement with all of you gab-BRO and SIS enthusiasts,

      Word Woman (aka Scientific Steph) 

 

Welcome to Partial Ellipsis of the Sun...

               Welcome to Partial Ellipsis of the Sun! 

                                            

                                   

Hello fellow scientists, writers, countrymen and countrywomen, lend me your years…years of experience of enjoyment of both science and writing. Both sides of your brain are…well, developed. :-)

You are the geologist who offers to write the reports accompanying exploration proposals because the proposed solution to the puzzle without commentary is only half of the story. You know that yes, a picture is worth a thousand words, but if you place well a mere seven words and just a comma or ellipsis, it can tell a remarkable story. 

You are the writer fascinated by every new development and discovery. Plate tectonics, older bristlecone pines, clades, dinosaurs with feathers discovered in China send you into orbit—perhaps to a partial ellipsis of the sun…Yes, ellipsis, eclipse, it’s all part of the story…

 I welcome your ideas for topics and commentary. I welcome input on how to make a blog fun and lively. I even welcome different ideas for the name (I’m not married to it)…Maybe just a tad too obscure? 

Next up: Volkswagen Bus to Smiley Face to Rubik’s Cube to Cell Phones to iPods to Smart Phones: What is wrong/right with this progression of decade avatars from the 1960’s to the 2010’s?! 

 I hope to post on Tuesdays. We’ll see how it goes. Happy belated National Punctuation Day…and Happy October! What an amazing month in which to launch a blog! 

Thanks for checking in… 

Word Woman (aka Scientific Steph)