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Rock study may have just revealed cause of Triassic mass extinction
Rocks from two hundred million years ago show us how everything died and how nothing is new.
Credit: Elenarts/Shutterstock
- A new study suggests that the mass extinction that gave dinosaurs the evolutionary upper hand was caused by oceanic oxygen deprivation.
- Using ratios of sulfur isotopes, researchers could estimate changes in ocean oxygen levels in ancient seas.
- The authors suggest a similar mechanism as that which can cause dead zones in oceans today caused a mass extinction.
Living on Earth isn't always easy. The fossil record is littered with enough mass extinction events to have once made theories that they occur in cycles seem feasible. The "Big Five" events each killed an average of 75 percent of all species alive at the time, with the largest one wiping more than 90 percent of them. While the question of what caused these events is interesting as a curiosity in and of itself, the problem also takes on an existential one, as most people would like to avoid the same fate as the trilobites.
To that end, a team of researchers based out of the UK, China, and Italy have investigated the causes behind one of the most massive die-offs in history. In a new paper published in Science Advances, they suggest a depletion in oxygen as a cause for the event at the end of the Triassic Era 201.3 million years ago.
How to tell what the world was like 201 million years ago using rocks
The mass extinction that ended the Triassic period was a massive die-off that saw somewhere between a quarter and a third of ocean life vanish alongside most large land animals. Plants were not spared a culling either, with perhaps 60 percent of plant species also dying. The event took less than 10,000 years to carry out this morbid work. This remarkable event paved the way for dinosaurs to become the dominant land animal during the Jurassic period, as most of their competition was dead.
Explanations for this event's cause have ranged from gradual climate change, to asteroid impacts, to rampant volcanism. New evidence suggests that ocean anoxia, the depletion of oxygen supplies in the ocean, played a large role.
The researchers examined the levels of two isotopes of sulfur in rocks that would have been on the seafloor during the extinction event from British Columbia, Sicily, and Northern Ireland. The two isotopes, 32S and 34S, can become trapped in limestone and other rocks and exist at different ratios depending on how much oxygen is in the water around them. By examining the changes in the ratio of the two isotopes in rocks formed at the time, we can know what was happening to oxygen levels in the oceans hundreds of millions of years ago.
The scientists noticed "large spikes" in the ratio of 34S to 32S in the samples from all of the locations, indicative of a substantial fall in the amount of oxygen available. These findings can be applied far beyond the sites the rock samples came from, suggesting that oxygen levels fell across large portions of the globe-spanning superocean, known as Panthalassa, that existed alongside Pangea.
And you thought the Dead Zone in the Gulf of Mexico was bad.
This study isn't the only one suggesting Ocean anoxia caused the extinction event. A previous study from 2017 reached a similar conclusion by measuring the trace uranium levels in rocks formed at the time. Similarly to the ratio of sulfur isotopes considered above, the amount of uranium in these rocks varies with the amount of oxygen. That study suggests that the low oxygen levels may have lasted 50,000 years after their initial fall, with a full 250,000 years needed before coral reefs could recover.
In the present day, the researchers hypothesize that this anoxia was connected to significant volcanic activity at the time. By releasing massive amounts of greenhouse gasses, this would have both acidified the oceans by increasing their carbon content and lowered their oxygen levels by raising global temperatures, as warm water holds less oxygen overall. Together, these effects can annihilate marine ecosystems. It is known that major volcanic activity was occurring at the time, lending credence to this hypothesis.
It's a good thing that nothing is causing the oceans to heat up and have lower oxygen levels these days! Oh, wait. Never mind.
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This is what aliens would 'hear' if they flew by Earth
A Mercury-bound spacecraft's noisy flyby of our home planet.
13 May, 2020
Image source: sdecoret on Shutterstock/ESA/Big Think
Surprising Science
- There is no sound in space, but if there was, this is what it might sound like passing by Earth.
- A spacecraft bound for Mercury recorded data while swinging around our planet, and that data was converted into sound.
- Yes, in space no one can hear you scream, but this is still some chill stuff.
First off, let's be clear what we mean by "hear" here. (Here, here!)
Sound, as we know it, requires air. What our ears capture is actually oscillating waves of fluctuating air pressure. Cilia, fibers in our ears, respond to these fluctuations by firing off corresponding clusters of tones at different pitches to our brains. This is what we perceive as sound.
All of which is to say, sound requires air, and space is notoriously void of that. So, in terms of human-perceivable sound, it's silent out there. Nonetheless, there can be cyclical events in space — such as oscillating values in streams of captured data — that can be mapped to pitches, and thus made audible.
BepiColombo
Image source: European Space Agency
The European Space Agency's BepiColombo spacecraft took off from Kourou, French Guyana on October 20, 2019, on its way to Mercury. To reduce its speed for the proper trajectory to Mercury, BepiColombo executed a "gravity-assist flyby," slinging itself around the Earth before leaving home. Over the course of its 34-minute flyby, its two data recorders captured five data sets that Italy's National Institute for Astrophysics (INAF) enhanced and converted into sound waves.
Into and out of Earth's shadow
In April, BepiColombo began its closest approach to Earth, ranging from 256,393 kilometers (159,315 miles) to 129,488 kilometers (80,460 miles) away. The audio above starts as BepiColombo begins to sneak into the Earth's shadow facing away from the sun.
The data was captured by BepiColombo's Italian Spring Accelerometer (ISA) instrument. Says Carmelo Magnafico of the ISA team, "When the spacecraft enters the shadow and the force of the Sun disappears, we can hear a slight vibration. The solar panels, previously flexed by the Sun, then find a new balance. Upon exiting the shadow, we can hear the effect again."
In addition to making for some cool sounds, the phenomenon allowed the ISA team to confirm just how sensitive their instrument is. "This is an extraordinary situation," says Carmelo. "Since we started the cruise, we have only been in direct sunshine, so we did not have the possibility to check effectively whether our instrument is measuring the variations of the force of the sunlight."
When the craft arrives at Mercury, the ISA will be tasked with studying the planets gravity.
Magentosphere melody
The second clip is derived from data captured by BepiColombo's MPO-MAG magnetometer, AKA MERMAG, as the craft traveled through Earth's magnetosphere, the area surrounding the planet that's determined by the its magnetic field.
BepiColombo eventually entered the hellish mangentosheath, the region battered by cosmic plasma from the sun before the craft passed into the relatively peaceful magentopause that marks the transition between the magnetosphere and Earth's own magnetic field.
MERMAG will map Mercury's magnetosphere, as well as the magnetic state of the planet's interior. As a secondary objective, it will assess the interaction of the solar wind, Mercury's magnetic field, and the planet, analyzing the dynamics of the magnetosphere and its interaction with Mercury.
Recording session over, BepiColombo is now slipping through space silently with its arrival at Mercury planned for 2025.
Study helps explain why motivation to learn declines with age
Research suggests that aging affects a brain circuit critical for learning and decision-making.
27 October, 2020
Photo by Reinhart Julian on Unsplash
Mind & Brain
As people age, they often lose their motivation to learn new things or engage in everyday activities. In a study of mice, MIT neuroscientists have now identified a brain circuit that is critical for maintaining this kind of motivation.
<p>This circuit is particularly important for learning to make decisions that require evaluating the cost and reward that come with a particular action. The researchers showed that they could boost older mice's motivation to engage in this type of learning by reactivating this circuit, and they could also decrease motivation by suppressing the circuit.</p><p>"As we age, it's harder to have a get-up-and-go attitude toward things," says Ann Graybiel, an Institute Professor at MIT and member of the McGovern Institute for Brain Research. "This get-up-and-go, or engagement, is important for our social well-being and for learning — it's tough to learn if you aren't attending and engaged."</p><p>Graybiel is the senior author of the study, which appears today in <em>Cell</em>. The paper's lead authors are Alexander Friedman, a former MIT research scientist who is now an assistant professor at the University of Texas at El Paso, and Emily Hueske, an MIT research scientist.</p>
<h3>Evaluating cost and benefit</h3><p>The striatum is part of the basal ganglia — a collection of brain centers linked to habit formation, control of voluntary movement, emotion, and addiction. For several decades, Graybiel's lab has been studying clusters of cells called striosomes, which are distributed throughout the striatum. Graybiel discovered striosomes many years ago, but their function had remained mysterious, in part because they are so small and deep within the brain that it is difficult to image them with functional magnetic resonance imaging (fMRI).</p><p>In recent years, Friedman, Graybiel, and colleagues including MIT research fellow Ken-ichi Amemori have discovered that striosomes <a href="https://news.mit.edu/2015/brain-circuit-controls-decisions-causing-anxiety-0528" target="_blank" rel="noopener noreferrer">play an important role</a> in a type of decision-making known as approach-avoidance conflict. These decisions involve choosing whether to take the good with the bad — or to avoid both — when given options that have both positive and negative elements. An example of this kind of decision is having to choose whether to take a job that pays more but forces a move away from family and friends. Such decisions often provoke great anxiety.</p><p>In a <a href="https://news.mit.edu/2016/neural-connections-linked-emotional-decision-making-0919" target="_blank" rel="noopener noreferrer">related study</a>, Graybiel's lab found that striosomes connect to cells of the substantia nigra, one of the brain's major dopamine-producing centers. These studies led the researchers to hypothesize that striosomes may be acting as a gatekeeper that absorbs sensory and emotional information coming from the cortex and integrates it to produce a decision on how to act. These actions can then be invigorated by the dopamine-producing cells.</p><p>The researchers later discovered that chronic stress has a major impact on this circuit and on this kind of emotional decision-making. In a <a href="https://news.mit.edu/2017/stress-can-lead-risky-decisions-1116" target="_blank" rel="noopener noreferrer">2017 study</a> performed in rats and mice, they showed that stressed animals were far more likely to choose high-risk, high-payoff options, but that they could block this effect by manipulating the circuit.</p>
<p>In the new <em>Cell</em> study, the researchers set out to investigate what happens in striosomes as mice learn how to make these kinds of decisions. To do that, they measured and analyzed the activity of striosomes as mice learned to choose between positive and negative outcomes.</p><p>During the experiments, the mice heard two different tones, one of which was accompanied by a reward (sugar water), and another that was paired with a mildly aversive stimulus (bright light). The mice gradually learned that if they licked a spout more when they heard the first tone, they would get more of the sugar water, and if they licked less during the second, the light would not be as bright.</p><p>Learning to perform this kind of task requires assigning value to each cost and each reward. The researchers found that as the mice learned the task, striosomes showed higher activity than other parts of the striatum, and that this activity correlated with the mice's behavioral responses to both of the tones. This suggests that striosomes could be critical for assigning subjective value to a particular outcome.</p><p>"In order to survive, in order to do whatever you are doing, you constantly need to be able to learn. You need to learn what is good for you, and what is bad for you," Friedman says.</p><p>"A person, or this case a mouse, may value a reward so highly that the risk of experiencing a possible cost is overwhelmed, while another may wish to avoid the cost to the exclusion of all rewards. And these may result in reward-driven learning in some and cost-driven learning in others," Hueske says.</p><p>The researchers found that inhibitory neurons that relay signals from the prefrontal cortex help striosomes to enhance their signal-to-noise ratio, which helps to generate the strong signals that are seen when the mice evaluate a high-cost or high-reward option.</p>
<h3>Loss of motivation</h3><p>Next, the researchers found that in older mice (between 13 and 21 months, roughly equivalent to people in their 60s and older), the mice's engagement in learning this type of cost-benefit analysis went down. At the same time, their striosomal activity declined compared to that of younger mice. The researchers found a similar loss of motivation in a mouse model of Huntington's disease, a neurodegenerative disorder that affects the striatum and its striosomes.</p><p>When the researchers used genetically targeted drugs to boost activity in the striosomes, they found that the mice became more engaged in performance of the task. Conversely, suppressing striosomal activity led to disengagement.</p><p>In addition to normal age-related decline, many mental health disorders can skew the ability to evaluate the costs and rewards of an action, from anxiety and depression to conditions such as PTSD. For example, a depressed person may undervalue potentially rewarding experiences, while someone suffering from addiction may overvalue drugs but undervalue things like their job or their family.</p><p>The researchers are now working on possible drug treatments that could stimulate this circuit, and they suggest that training patients to enhance activity in this circuit through biofeedback could offer another potential way to improve their cost-benefit evaluations.</p><p>"If you could pinpoint a mechanism which is underlying the subjective evaluation of reward and cost, and use a modern technique that could manipulate it, either psychiatrically or with biofeedback, patients may be able to activate their circuits correctly," Friedman says.</p><p>The research was funded by the CHDI Foundation, the Saks Kavanaugh Foundation, the National Institutes of Health, the Nancy Lurie Marks Family Foundation, the Bachmann-Strauss Dystonia and Parkinson's Foundation, the William N. and Bernice E. Bumpus Foundation, the Simons Center for the Social Brain, the Kristin R. Pressman and Jessica J. Pourian '13 Fund, Michael Stiefel, and Robert Buxton.</p><p>Reprinted with permission of <a href="http://news.mit.edu/" target="_blank" rel="noopener noreferrer">MIT News</a>. Read the <a href="https://news.mit.edu/2020/why-learn-motivate-age-decline-1027" target="_blank">original article</a>.</p>
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Scientists discover why fish evolved limbs and left water
Researchers find a key clue to the evolution of bony fish and tetrapods.
27 October, 2020
Surprising Science
- A new study says solar and lunar tide impacts led to the evolution of bony fish and tetrapods.
- The scientists show that tides created tidal pools, stranding fish and forcing them to get out of the water.
- The researchers ran computer simulations to get their results.
<p>Tides influenced by the sun and the moon were likely the reason why fish developed limbs and early tetrapods evolved, found new research.</p><p>The groundbreaking study took a look at tides during the Late Silurian—Devonian periods, which happened between 420 million years ago and 380 million years ago.</p><p>The scientists built their work on the theory that the Moon's mass and specific location along its orbit can greatly affect vast tidal ranges across Earth and can create tidal pools. Because they are isolated from each other, the pools provided the biological motivation for fish stranded by high tides to eventually grow limbs. </p>
<p>The study involved researchers from from UK's Bangor University and Oxford University as well as Uppsala University in Sweden. They devised very detailed numerical simulations that proved the existence of large tides during the period they studied. They are first to tie tidal hydrodynamics to an evolutionary biological event, states the <a href="https://www.ox.ac.uk/news/2020-10-23-large-tides-may-have-been-key-factor-evolution-bony-fish-and-tetrapods" target="_blank">press release</a> from the University of Oxford.</p><p>To come up with the simulations, the scientists employed <em>paleogeography</em>, the study of historical geography, to reconstruct the Earth's continents within the numerical model. The calculations showed tides over four meters happening around the South China block. That area holds the known origin site of the earliest bony fish we know and has been a treasure-trove of the earliest fossils of that nature. Geological evidence also supports changes in tides to be lined to these fossils.</p>
Neil deGrasse Tyson Explains the Tides
<span style="display:block;position:relative;padding-top:56.25%;" class="rm-shortcode" data-rm-shortcode-id="9913a65f847775722d7c23d40d78938b"><iframe type="lazy-iframe" data-runner-src="https://www.youtube.com/embed/dBwNadry-TU?rel=0" width="100%" height="auto" frameborder="0" scrolling="no" style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe></span><p style="margin-left: 20px;">"Large tidal ranges could have fostered both the evolution of air-breathing organs in <a href="https://en.wikipedia.org/wiki/Osteichthyes" target="_blank">osteichthyans</a> to facilitate breathing in oxygen-depleted tidal pools, and the development of weight-bearing tetrapod limbs to aid navigation within the intertidal zones," states the paper.</p><p>The researchers believe further tidal simulations from early Earth can be used to recreate that far past with greater detail. The findings can help us understand more what roles tides played in diversifying early vertebrates or in causing extinction events. </p><p>Check out the study published in <a href="https://royalsocietypublishing.org/doi/10.1098/rspa.2020.0355" target="_blank"><em>Proceedings of the Royal Society A</em>.</a></p>
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Coronavirus
Optimism may be dangerous in a pandemic, say behavioral psychologists
Most people believe themselves to be less at risk from COVID-19 than others similar to them, according to a recent UCL survey conducted in the U.S.
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