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John_the_Younger

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Re: Earth through time
« Reply #50 on: September 14, 2023, 06:02:56 PM »
Direct signs of what caused the Palaeocene-Eocene thermal maximum [PETM - 55 million years ago - a time often looked to as being similar to what humans are doing today]
Earth Logs (new website)

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The evidence points to explosive vents formed by massive degassing of deeper sediments induced by igneous intrusions. Such systems are common around active ocean-floor rifts: ‘black-‘ and ‘white smokers’, but those off Norway formed in shallow water. That has an important bearing on their potency during the PETM. Deep hydrothermal systems may emit methane, but it is oxidised to CO2 in seawater. Those very close to the surface vent their gas almost directly into the atmosphere before such oxidation can consume methane. Intrusive sills also underlie the eastern continental margin of Greenland, so such explosive hydrothermal vents may have been widespread during the initial rifting of the North Atlantic’.

kassy

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Re: Earth through time
« Reply #51 on: October 10, 2023, 06:23:27 PM »
Plate tectonic surprise: Geologist unexpectedly finds remnants of a lost mega-plate

Geologists have reconstructed a massive and previously unknown tectonic plate that was once one-quarter the size of the Pacific Ocean. The team had predicted its existence over 10 years ago based on fragments of old tectonic plates found deep in the Earth’s mantle. To the lead researchers surprise, she found that oceanic remnants on northern Borneo must have belonged to the long-suspected plate, which scientists have named Pontus. She has now reconstructed the entire plate in its full glory.


Utrecht University geologist Suzanna van de Lagemaat has reconstructed a massive and previously unknown tectonic plate that was once one-quarter the size of the Pacific Ocean. Her colleagues in Utrecht had predicted its existence over 10 years ago based on fragments of old tectonic plates found deep in the Earth's mantle. Van de Lagemaat reconstructed lost plates through field research and detailed investigations of the mountain belts of Japan, Borneo, the Philippines, New Guinea, and New Zealand. To her surprise, she found that oceanic remnants on northern Borneo must have belonged to the long-suspected plate, which scientists have named Pontus. She has now reconstructed the entire plate in its full glory. Suzanna van de Lagemaat will defend her dissertation on this plate tectonics puzzle at Utrecht University on Friday, October 13.

Understanding the movements of the tectonic plates that make up the earth's rigid outer shell is essential to understand the planet's geological history. The movements of these plates strongly influenced how the planet's paleogeography and climate have changed over time, and even where to find rare metals. But large oceanic plates from the geological past have since disappeared into the earth's mantle by means of subduction. They have left behind only fragments of rock hidden in mountain belts. Van de Lagemaat studied the planet's most complicated plate tectonic region: the area around the Philippines. "The Philippines is located at a complex junction of different plate systems. The region almost entirely consists of oceanic crust, but some pieces are raised above sea level, and show rocks of very different ages."

Reconstruction

Using geological data, Van de Lagemaat first reconstructed the movements of the current plates in the region between Japan and New Zealand. That revealed how large the area was of plates that must have disappeared in the current western Pacific region. "We also conducted field work on northern Borneo, where we found the most important piece of the puzzle. We thought we were dealing with relicts of a lost plate that we already knew about. But our magnetic lab research on those rocks indicated that our finds were originally from much farther north, and had to be remnants of a different, previously unknown plate." But the important realisation was yet to come. "11 years ago, we thought that the remnants of Pontus might lie in northern Japan, but we'd since refuted that theory," explains Douwe van Hinsbergen, Van de Lagemaat's PhD supervisor. "It was only after Suzanna had systematically reconstructed half of the 'Ring of Fire' mountain belts from Japan, through New Guinea, to New Zealand that the proposed Pontus plate revealed itself, and it included the rocks we studied on Borneo."

Relics

The relics of Pontus are not only located on northern Borneo, but also on Palawan, an island in the Western Philippines, and in the South China Sea. Van de Lagemaat's research also showed that a single coherent plate tectonic system stretched from southern Japan to New Zealand, and it must have existed for at least 150 million years. That is also a new discovery in the field.

Waves

The previous predictions of the existence of Pontus were made possible because a subducted plate leaves behind traces when it 'sinks' into the earth's mantle: zones in the mantle with anomalous temperatures or compositions. These anomalies can be observed when seismographs pick up signals from earthquakes. Earthquakes send waves through Earth's interior, and when they travel through an anomaly, such as a fragment from an old plate, the anomaly produces a disruption of the signal. Geologists can trace these disruptions to the existence of phenomena in the mantle, such as fragments of tectonic plates. That allows them to look 300 million years into the past; older plate fragments have 'dissolved' at the boundary between the mantle and the core. The study from 11 years ago showed that a large subduction zone must have run through the western paleo-Pacific Ocean, which separated the known Pacific plates in the east from the hypothetical Pontus plate in the west. This hypothesis has now been independently demonstrated by Van de Lagemaat's research.

https://www.sciencedaily.com/releases/2023/10/231009191657.htm
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kassy

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Re: Earth through time
« Reply #52 on: October 12, 2023, 04:43:04 PM »
New research reveals why and when the Sahara Desert was green


A pioneering study has shed new light on North African humid periods that have occurred over the past 800,000 years and explains why the Sahara Desert was periodically green.

The research, published in Nature Communications, showed periodic wet phases in the Sahara were driven by changes in Earth’s orbit around the Sun and were suppressed during the ice ages.

For the first time, climate scientists simulated the historic intervals of ‘greening’ of the Sahara, offering evidence for how the timing and intensity of these humid events were also influenced remotely by the effects of large, distant, high-latitude ice sheets in the Northern Hemisphere.

Lead author Dr Edward Armstrong, a climate scientist at the University of Helsinki and University of Bristol, said: “The cyclic transformation of the Sahara Desert into savannah and woodland ecosystems is one of the most remarkable environmental changes on the planet.

“Our study is one of the first climate modelling studies to simulate the African Humid Periods with comparable magnitude to what the palaeoclimate observations indicate, revealing why and when these events occurred.”

There is widespread evidence that the Sahara was periodically vegetated in the past, with the proliferation of rivers, lakes and water-dependent animals such as hippos, before it became what is now desert. These North African Humid Periods may have been crucial in providing vegetated corridors out of Africa, allowing the dispersal of various species, including early humans, around the world.

The so-called ‘greenings’ are thought to have been driven by changes in Earth’s orbital conditions, specifically Earth’s orbital precession. Precession refers to how Earth wobbles on its axis, which influences seasonality (i.e. the seasonal contrast) over an approximate 21,000-year cycle. These changes in precession determine the amount of energy received by the Earth in different seasons, which in turn controls the strength of the African Monsoon and the spread of vegetation across this vast region.

A major barrier to understanding these events is that the majority of climate models have been unable to simulate the amplitude of these humid periods, so the specific mechanisms driving them have remained uncertain.

This study deployed a recently-developed climate model to simulate the North African Humid periods to greatly advance understanding of their driving mechanisms.

The results confirm the North African Humid Periods occurred every 21,000 years and were determined by changes in Earth’s orbital precession. This caused warmer summers in the Northern Hemisphere, which intensified the strength of the West African Monsoon system and increased Saharan precipitation, resulting in the spread of savannah-type vegetation across the desert.

The findings also show the humid periods did not occur during the ice ages, when there were large glacial ice sheets covering much of the high latitudes. This is because these vast ice sheets cooled the atmosphere and suppressed the tendency for the African monsoon system to expand. This highlights a major teleconnection between these distant regions, which may have restricted the dispersal of species, including humans, out of Africa during the glacial periods of the last 800,000 years.

Co-author Paul Valdes, Professor of Physical Geography at the University of Bristol, said: “We are really excited about the results. Traditionally, climate models have struggled to represent the extent of the ‘greening’ of the Sahara. Our revised model successfully represents past changes and also gives us confidence in their ability to understand future change.”

The research, including climate scientists from the University of Birmingham, is part of a Kone Foundation-funded project at the University of Helsinki, which studies the impacts of climate on past human distributions and evolution of their ecological niche.

Co-author Miikka Tallavaara, Assistant Professor of Hominin Environments at the University of Helsinki, said: “The Sahara region is kind of a gate controlling the dispersal of species between both North and Sub-Saharan Africa, and in and out of the continent.

“The gate was open when Sahara was green and closed when deserts prevailed. This alternation of humid and arid phases had major consequences for the dispersal and evolution of species in Africa. Our ability to model North African Humid periods is a major achievement and means we are now also better able to model human distributions and understand the evolution of our genus in Africa.”

https://www.sciencedaily.com/releases/2023/09/230913122641.htm

North African humid periods over the past 800,000 years
https://www.nature.com/articles/s41467-023-41219-4
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kassy

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Re: Earth through time
« Reply #53 on: November 04, 2023, 01:24:52 PM »
The remains of an ancient planet lie deep within Earth


n the 1980s, geophysicists made a startling discovery: two continent-sized blobs of unusual material were found deep near the center of the Earth, one beneath the African continent and one beneath the Pacific Ocean. Each blob is twice the size of the Moon and likely composed of different proportions of elements than the mantle surrounding it.

Where did these strange blobs -- formally known as large low-velocity provinces (LLVPs) -- come from? A new study led by Caltech researchers suggests that they are remnants of an ancient planet that violently collided with Earth billions of years ago in the same giant impact that created our Moon.

The study, published in the journal Nature on November 1, also proposes an answer to another planetary science mystery. Researchers have long hypothesized that the Moon was created in the aftermath of a giant impact between Earth and a smaller planet dubbed Theia, but no trace of Theia has ever been found in the asteroid belt or in meteorites. This new study suggests that most of Theia was absorbed into the young Earth, forming the LLVPs, while residual debris from the impact coalesced into the Moon.

The research was led by Qian Yuan, O.K. Earl Postdoctoral Scholar Research Associate in the laboratories of both Paul Asimow (MS '93, PhD '97), the Eleanor and John R. McMillan Professor of Geology and Geochemistry; and Michael Gurnis, the John E. And Hazel S. Smits Professor of Geophysics and Clarence R. Allen Leadership Chair, director of Caltech's Seismological Laboratory, and director of the Schmidt Academy for Software Engineering at Caltech.

Scientists first discovered the LLVPs by measuring seismic waves traveling through the earth. Seismic waves travel at different speeds through different materials, and in the 1980s, the first hints emerged of large-scale three-dimensional variations deep within the structure of Earth. In the deepest mantle, the seismic wave pattern is dominated by the signatures of two large structures near the Earth's core that researchers believe possess an unusually high level of iron. This high iron content means the regions are denser than their surroundings, causing seismic waves passing through them to slow down and leading to the name "large low velocity provinces."

Yuan, a geophysicist by training, was attending a seminar about planet formation given by Mikhail Zolotov, a professor at Arizona State University, in 2019. Zolotov presented the giant-impact hypothesis, while Qian noted that the Moon is relatively rich in iron. Zolotov added that no trace had been found of the impactor that must have collided with the Earth.

"Right after Mikhail had said that no one knows where the impactor is now, I had a 'eureka moment' and realized that the iron-rich impactor could have transformed into mantle blobs," says Yuan.

Yuan worked with multidisciplinary collaborators to model different scenarios for Theia's chemical composition and its impact with Earth. The simulations confirmed that the physics of the collision could have led to the formation of both the LLVPs and the Moon. Some of Theia's mantle could have become incorporated into the Earth's own, where it ultimately clumped and crystallized together to form the two distinct blobs detectable today at Earth's core-mantle boundary today; other debris from the collision mixed together to form the Moon.

Given such a violent impact, why did Theia's material clump into the two distinct blobs instead of mixing together with the rest of the forming planet? The researchers' simulations showed that much of the energy delivered by Theia's impact remained in the upper half of the mantle, leaving Earth's lower mantle cooler than estimated by earlier, lower-resolution impact models. Because the lower mantle was not totally melted by the impact, the blobs of iron-rich material from Theia stayed largely intact as they sifted down to the base of the mantle, like the colored masses of paraffin wax in a turned-off lava lamp. Had the lower mantle been hotter (that is, if it had received more energy from the impact), it would have mixed more thoroughly with the iron-rich material, like the colors in a stirred pot of paints.

The next steps are to examine how the early presence of Theia's heterogeneous material deep within the earth might have influenced our planet's interior processes, such as plate tectonics.

"A logical consequence of the idea that the LLVPs are remnants of Theia is that they are very ancient," Asimow says. "It makes sense, therefore, to investigate next what consequences they had for Earth's earliest evolution, such as the onset of subduction before conditions were suitable for modern-style plate tectonics, the formation of the first continents, and the origin of the very oldest surviving terrestrial minerals."

https://www.sciencedaily.com/releases/2023/11/231101134924.htm

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johnm33

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Re: Earth through time
« Reply #54 on: November 04, 2023, 04:16:23 PM »
I have a theory about these low velocity zones too. The outer core being composed of liquid crystalline iron/nickel/manganese with low melt point metal ore bodies mixed in, the densest near the equatorial zone. The heavy metals are saturated with H+/protons, when they break through into the Si/O dominated mineralls of the deep mantle they react altering the chemical make up and density of the near-core minerology. These molten blobs being much less dense slow siesmic transmissions.

kassy

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Re: Earth through time
« Reply #55 on: March 19, 2024, 05:58:17 PM »
Strange rock formations beneath the Pacific Ocean could change our understanding of early Earth


The answer lies in some of the earliest extensive relics of Earth's surface, found in a remote corner of southern Africa's highveld—a region known to geologists as the Barberton Greenstone Belt.

The geological formations in this region have proved difficult to decipher, despite many attempts. But our new research has shown the key to cracking this code lies in geologically young rocks laid down on the seafloor of the Pacific Ocean off the coast of New Zealand.

This has opened up a new perspective on what our planet looked like when it was still young.

Our work began with a new, detailed geological map (by Cornel de Ronde) of part of the Barberton Greenstone Belt. This has revealed a fragment of the ancient deep seafloor, created some 3.3 billion years ago.

There was, however, something very strange about this seafloor, and it has taken our study of rocks laid down in New Zealand, at the other end of the Earth's long history, to make sense of it.

We argue that the widely held view of the early Earth as a hotter place, free of earthquakes and with a surface so weak it was unable to form rigid plates is wrong.

Instead, the young Earth was continually rocked by large earthquakes, triggered as one tectonic plate slid beneath another in a subduction zone as part of plate tectonics—just like New Zealand today.

Jumbled rocks
Geologists have long found it hard to interpret the ancient rocks of the Barberton Greenstone Belt.

Layers that formed on land or in shallow water—for example, beautiful crystals of barite that had crystallized as evaporites, or the remains of bubbling mud pools—are found sitting on top of rocks that accumulated on the deep seafloor. Blocks of volcanic rock, chert, sandstone and conglomerate lie topsy turvy and jumbled up.

We realized this map looked remarkably similar to a geological map (by Simon Lamb) made of the aftermath of much more recent submarine landslides. These were triggered by great earthquakes along New Zealand's largest fault, the megathrust in the Hikurangi subduction zone.

The bedrock is made of a jumble of sedimentary rocks, originally laid down on the seafloor off the coast of New Zealand some 20 million years ago. This region lay on the edges of the deep oceanic trench, where the Pacific tectonic plate is sliding down in a subduction zone triggering frequent large earthquakes.

The rocks in New Zealand are the key to reading the geological record in the Barberton Greenstone Belt.

What was once thought to be untranslatable turns out to be a remnant of a gigantic landslide containing sediments deposited both on land or in very shallow water, jumbled with those that accumulated on the deep seafloor.

...

https://phys.org/news/2024-03-strange-formations-beneath-pacific-ocean.html
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kassy

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Re: Earth through time
« Reply #56 on: March 19, 2024, 06:26:43 PM »
Mantle convection linked to seaway closure that transformed Earth's oceanographic circulation patterns

Continental drift is a concept familiar to many, referencing the movement of Earth's continents due to shifting tectonic plates over millions of years, splitting one globe-spanning supercontinent into the configuration we see today. Alongside this there have been smaller land mass movements that have opened seaways, affecting ocean circulation patterns and climate.

One such occurrence during the Paleogene (66 to ~23 million years ago, Ma) led to an oceanic connection from the Neotethys Ocean, situated north of India and Australia, to the polar Arctic Ocean. This significant shallow ocean seaway is known as the West Siberian Seaway.

The mechanisms by which this seaway formed are the focus of new research, published in Earth and Planetary Science Letters. Dr. Eivind Straume, of NORCE Norwegian Research Center AS and the Bjerknes Center for Climate Research, Norway, and colleagues turned to the influence of Earth's mantle to investigate how its flow and forces resulting in surface topography (known as dynamic topography) impacted the seaway's evolution and the paleoenvironmental implications of this.

...

Reconstructions show Eurasia was covered by a shallow seaway in the Eocene (56–33.9 Ma), while Arabia was also flooded by an epicontinental (inland) sea at this time until it emerged to become terrestrial by Late Miocene (~11.6 Ma). The collision of Eurasia and Arabia ultimately led to the closure of the Tethys Seaway ~20 Ma, a deep passage that linked the Atlantic and Indo-Pacific oceans. Modern ocean circulation patterns stem from this closure, affecting the transfer of heat, nutrients and water masses within and across ocean basins from the equator to the poles.

"The closure of the Tethys Seaway was important for ocean circulation in the sense that it limited transport from the Indian to the Atlantic Ocean, which could influence the strength of the Atlantic Meridional Overturning Circulation and thereby impact climate globally," Dr. Straume says.

"Had it not closed, the overturing in the Atlantic could have been weaker than it is today. Additionally, it likely had some impact on the development of modern-like Asian monsoons. The closure also formed a land bridge that mammals walked across, playing a role in their biogeographic dispersal across Northern Africa, Arabia and Eurasia."

...

https://phys.org/news/2024-03-mantle-convection-linked-seaway-closure.html
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