It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Atmospheric carbon dioxide continued its rapid rise in 2019, with the average for May peaking at 414.7 parts per million (ppm) at NOAA's Mauna Loa Atmospheric Baseline Observatory.
The measurement is the highest seasonal peak recorded in 61 years of observations on top of Hawaii's largest volcano and the seventh consecutive year of steep global increases in concentrations of carbon dioxide (CO2), according to data published today by NOAA and Scripps Institution of Oceanography.
The 2019 peak value was 3.5 ppm higher than the 411.2 ppm peak in May 2018 and marks the second-highest annual jump on record. Monthly CO2 values at Mauna Loa first breached the 400 ppm threshold in 2014.
"It's critically important to have these accurate, long-term measurements of CO2 in order to understand how quickly fossil fuel pollution is changing our climate," said Pieter Tans, senior scientist with NOAA's Global Monitoring Division.
"These are measurements of the real atmosphere. They do not depend on any models, but they help us verify climate model projections, which if anything, have underestimated the rapid pace of climate change being observed."
The concentration of CO2 in the atmosphere increases every year, and the rate of increase is accelerating. The early years at Mauna Loa saw annual increases averaging about 0.7 ppm per year, increasing to about 1.6 ppm per year in the 1980s and 1.5 ppm per year in the 1990s. The growth rate rose to 2.2 ppm per year during the last decade. There is abundant and conclusive evidence that the acceleration is caused by increased emissions, Tans said.
The Mauna Loa data, together with measurements from sampling stations around the world, are collected by NOAA's Global Greenhouse Gas Reference Network and produce a foundational research dataset for international climate science.
The highest monthly mean CO2 value of the year occurs in May, just before plants start to remove large amounts of the greenhouse gas from the atmosphere during the northern hemisphere growing season. In the northern fall, winter and early spring, plants and soils give off CO2, which cause levels to rise through May.
Charles Keeling was the first to observe this seasonal rise and subsequent fall in CO2 levels embedded within annual increases, a cycle now known as the Keeling Curve.
Source: NOAA [June 04, 2019] Read more at https://archaeologynewsnetwork.blogspot.com/2019/06/carbon-dioxide-levels-in-atmosphere-hit.html#vwHPSyvhuaiA7kpv.99
A new study by University of Alberta scientists shows that banded iron formations originated from oxidized iron, confirming the relevance and accuracy of existing models--a finding of great importance to the geological community.
Banded iron formations, such as this one pictured in Western Australia, precipitated out of the Earth's early oceans billions of years ago, and are providing new clues to the evolution of ancient seawater and the microbes that inhabited it [Credit: Tom Price]
Banded iron formations are a distinct type of sedimentary rock with layers of iron deposited as horizontal bands. The majority of these formations formed over the last 2.5 billion years and are a major source of iron today. "We've been using banded iron formations with great success to track the evolution of seawater chemistry and evolution of the biosphere," explained Kurt Konhauser, professor in the Department of Earth and Atmospheric Sciences and co-author on the paper. "But these experiments are based on the assumption that we understand the primary minerals that compose these rocks."
In the last decade, a new model was proposed, suggesting that the formations began as ferrous iron that was later oxidized by oxygen in the environment--a model that, if correct, would require a major paradigm shift in this area of study.
To examine this possibility, a group of researchers led by Konhauser's PhD student Leslie Robbins tested the theory using a hydrogeological model, designed to determine how long it would take oxygen to oxidize such a formation. The research team included Professor Ben Roston, Assistant Professor Daniel Alessi, and Professor Larry Heaman.
"Essentially, we found that this would be possible in only one per cent of cases in the suggested time frame of 250 million years," said Konhauser. "Moreover, we had to create unrealistic conditions in order to make the new proposed model work--for instance, an extremely steep slope, or rock that was actually sand, or a great deal of oxygen."
These results confirmed that the newly proposed model is inaccurate, indicating that existing models and our current understanding remains the most effective method of studying banded iron formations.
"This is a powerful result that stems from the simple question about whether recently proposed models for banded iron formations are plausible when extrapolated to the size of a depositional basin," said Robbins, now a postdoctoral fellow at Yale University in New Haven, United States. "This result has fundamental implications for the formation of these deposits, and this work benefited greatly from strong collaborations both within Earth and Atmospheric Sciences and with our external collaborators."
One of the world's most important plant families has a history extending much farther south than any live or fossil specimen previously recorded, as shown by chinquapin fruit and leaf fossils unearthed in Patagonia, Argentina, according to researchers.
Discovery photo of the mature Castanopsis fruiting spike fossil with four nuts enclosed in scaly cupules, showing the part and counterpart on the split surface at Laguna del Hunco [Credit: Peter Wilf, Penn State University]
"The oak and beech family is recognized everywhere as one of the most important plant groups and has always been considered northern," said Peter Wilf, professor of geosciences and associate in the Earth and Environmental Systems Institute, Penn State. "We're adding a huge spatial dimension to the history of the Fagaceae family, and that's exciting." The plant family also includes chestnuts and the closely related chinquapins.
Common in the Northern Hemisphere and Asian tropics, Fagaceae cross the equator only in Southeast Asia, and even there just barely. The latest study, published in Science, extends the family's biogeographical history and suggests a Gondwanan supercontinent legacy in Asian rainforests larger than previously thought.
The researchers first found fossils resembling some oak leaves, with straight secondary veins and one tooth per secondary vein, at Laguna del Hunco, Chubut province. The leaves comprise about 10 percent of the thousands of 52-million-year-old leaf fossils, representing almost 200 species, found at the site over two decades in a long-term project between Penn State, Cornell University and Museo Paleontológico Egidio Feruglio (MEF), Trelew, Argentina.
Detail of the mature Castanopsis fruiting spike fossil with four nuts, dark and turned to coal, enclosed in scaly cupules. Cupule at top is splitting open [Credit: Peter Wilf, Penn State University]
For years the researchers hesitated to classify the leaves, because paleobotanist Edward Berry had assigned similar fossils to another family, and any claim of Fagaceae at so remote a location would require much more supporting evidence.
Later, the team unearthed rare fruit fossils -- two fruit clusters, one with more than 110 immature fruits -- at the site and compared them to living relatives. They found that these were fossils of ancient Castanopsis, an Asian chinquapin that today dominates the biodiverse, lower elevation mountain rainforests of Southeast Asia.
"One of the first clues was a little lip where the fruit is splitting open," Wilf said. "I recognized this lip as being similar to the fruit of the Japanese chinquapin. Then I realized there's a nut inside."
Detail of a single immature fruit of living Castanopsis acuminatissima, New Guinea, showing scaly surface and preservation of three slender styles (pollen-receiving organs) at top [Credit: Peter Wilf, Penn State University]
The nuts are fully encased in a scaly outer covering, or cupule, that splits open when the fruits mature. The cupules are arranged on a spike-like fruiting axis, and the young nuts retain delicate parts from their flowering stage. Their features are just like the living Castanopsis, Wilf said, and the fruits confirm that the leaves are Fagaceae.
"This is the first confirmed evidence that Fagaceae, considered restricted to the Northern Hemisphere, was in the Southern Hemisphere," said Maria Gandolfo, associate professor, Cornell University. "This is remarkable and allows us to rethink the origins of the fossil flora."
The fossils date to the early Eocene 52.2 million years ago. They are the only fossilized or living Fagaceae ever found south of the Malay Archipelago, the island chain just north of Australia.
Large fossil Fagaceae leaf from Laguna del Hunco with well-preserved details [Credit: Peter Wilf, Penn State University]
During the globally warm early Eocene there was no polar ice, and South America, Antarctica and Australia had not completely separated, comprising the final stage of the Gondwanan supercontinent. The researchers think animals had helped disperse the chinquapin's ancestors from North to South America at an earlier time. The plants thrived in the wet Patagonian rainforest, whose closest modern analog is the mountain rainforests of New Guinea.
"Before the current semi-desert conditions, trees covered Patagonia," said Rubén Cúneo, director of MEF. "Changes in climatic conditions turned it into a shrubland, and the trees were displaced."
The chinquapins may have also ranged into then-adjacent Antarctica and on to Australia, said Wilf. Castanopsis may have survived in Australia until the continent collided with Southeast Asia, where today chinquapins are keystone species, providing forest structure and food and habitat for birds, insects and mammals.
The Laguna del Hunco fossil site in Chubut, Patagonian Argentina. Paleontologists at centre of frame are collecting diverse plant fossils, including abundant leaves of Fagaceae [Credit: Peter Wilf, Penn State University]
"We're finding, in the same rocks as Castanopsis, fossils of many other plants that live with it today in New Guinea and elsewhere, including ferns, conifers and flowering plants," said Wilf. "You can trace some of the associations with Castanopsis seen in Eocene Argentina to southern China and beyond."
Today, Castanopsis plays an important role in intercepting year-round mountain precipitation that delivers clean water for drinking, fishing and agriculture to more than half a billion people and sustains diverse freshwater and coastal ecosystems. However, humans are clearing these rainforests for timber, development and crop cultivation, and modern climate change is increasing droughts and fire frequency.
"These plants are adaptable if given time and space," Wilf said, adding Castanopsis' trek from Patagonia to Southeast Asia occurred over millions of years and thousands of miles. "But the pace of change today is hundreds of times faster than in geologic time. The animals that depend on these plants are adaptable only to the extent that the plants are, and we are one of the animals that depend on this system. If we lose mountain rainforests, really fast we lose reliable water flows for agriculture, clean coral reefs offshore, biodiversity and much more."
This study has implications for extinction in the face of climate change, according to Kevin Nixon, professor and L.H. Bailey Hortorium curator, Cornell University. He said Castanopsis went extinct in Patagonia due to a major extinction caused by the slow cooling and drying of the climate that occurred with the glaciation of Antarctica and the rise of the Andes.
"Those kinds of climate changes can have massive effects on biodiversity," Nixon said. "The relevance of understanding this is we can start to look at extinction processes. The better we can understand what causes extinction, the better we can deal with it."
Chinquapin fossils found in Patagonia, Argentina are 52.2 million years old and represent
the earliest fruit of this family of trees and were found south of the tropics
[Credit: Strategic Communications, Penn State University]
Glacial Sediments Greased The Gears Of Plate Tectonics
Earth's outer layer is composed of giant plates that grind together, sliding past or dipping beneath one another, giving rise to earthquakes and volcanoes. These plates also separate at undersea mountain ridges, where molten rock spreads from the centers of ocean basins.
This view of the Grand Canyon shows the Great Unconformity, a boundary where nearly a billion years' worth of sedimentary deposits is missing from the geologic record. The boundary can be seen at roughly the middle of this image, separating the older, lumpy and angular rocks below from the younger horizontal layers above. New research suggests that the missing sediments, likely scrubbed away by glaciers during the global "snowball Earth" that ended roughly 635 million years ago, washed away to the oceans, where they lubricated subduction faults and kick-started the modern age of plate tectonics [Credit: USGS/Alex Demas]
But this was not always the case. Early in Earth's history, the planet was covered by a single shell dotted with volcanoes--much like the surface of Venus today. As Earth cooled, this shell began to fold and crack, eventually creating Earth's system of plate tectonics.
According to new research, the transition to plate tectonics started with the help of lubricating sediments, scraped by glaciers from the slopes of Earth's first continents. As these sediments collected along the world's young coastlines, they helped to accelerate the motion of newly formed subduction faults, where a thinner oceanic plate dips beneath a thicker continental plate.
The new study, published this week in the journal Nature, is the first to suggest a role for sediments in the emergence and evolution of global plate tectonics. Michael Brown, a professor of geology at the University of Maryland, co-authored the research paper with Stephan Sobolev, a professor of geodynamics at the GFZ German Research Centre for Geosciences in Potsdam.
The findings suggest that sediment lubrication controls the rate at which Earth's crust grinds and churns. Sobolev and Brown found that two major periods of worldwide glaciation, which resulted in massive deposits of glacier-scrubbed sediment, each likely caused a subsequent boost in the global rate of plate tectonics.
The most recent such episode followed the "snowball Earth" that ended sometime around 635 million years ago, resulting in Earth's modern plate tectonic system.
"Earth hasn't always had plate tectonics and it hasn't always progressed at the same pace," Brown said. "It's gone through at least two periods of acceleration. There's evidence to suggest that tectonics also slowed to a relative crawl for nearly a billion years. In each case, we found a connection with the relative abundance--or scarcity--of glacial sediments."
Just as a machine needs grease to keep its parts moving freely, plate tectonics operates more efficiently with lubrication. While it may be hard to confuse the gritty consistency of clay, silt, sand and gravel with a slippery grease, the effect is largely the same at the continental scale, in the ocean trenches where tectonic plates meet.
"The same dynamic exists when drilling Earth's crust. You have to use mud--a very fine clay mixed with water or oil--because water or oil alone won't work as well," Brown said. "The mud particles help reduce friction on the drill bit. Our results suggest that tectonic plates also need this type of lubrication to keep moving."
Previous research on the western coast of South America was the first to identify a relationship between sediment lubrication and friction along a subduction fault. Off the coast of northern Chile, a relative lack of sediment in the fault trench creates high friction as the oceanic Nazca plate dips beneath the continental South America plate. This friction helped to push the highest peaks of the central Andes Mountains skyward as the continental plate squashed and deformed.
In contrast, further south there is a higher sediment load in the trench, resulting in less friction. This caused less deformation of the continental plate and, consequently, created smaller mountain peaks. But these findings were limited to one geographic area.
For their study, Sobolev and Brown used a geodynamic model of plate tectonics to simulate the effect of sediment lubrication on the rate of subduction. To verify their hypothesis, they checked for correlations between known periods of widespread glaciation and previously published data that indicate the presence of continental sediment in the oceans and trenches. For this step, Sobolev and Brown relied on two primary lines of evidence: the chemical signature of the influence of continental sediments on the chemistry of the oceans and indicators of sediment contamination in subduction-related volcanoes, much like those that make up today's "ring of fire" around the Pacific Ocean.
According to Sobolev and Brown's analysis, plate tectonics likely emerged on Earth between 3 and 2.5 billion years ago, around the time when Earth's first continents began to form. This time frame also coincides with the planet's first continental glaciation.
A major boost in plate tectonics then occurred between 2.2 to 1.8 billion years ago, following another global ice age that scrubbed massive amounts of sediments into the fault trenches at the edges of the continents.
The next billion years, from 1.75 billion to 750 million years ago, saw a global reduction in the rate of plate tectonics. This stage of Earth's history was so sedate, comparatively speaking, that it earned the nickname "the boring billion" among geologists.
Later, following the global "snowball Earth" glaciation that ended roughly 635 million years ago, the largest surface erosion event in Earth's history may have scrubbed more than a vertical mile of thickness from the surface of the continents. According to Sobolev and Brown, when these sediments reached the oceans, they kick-started the modern phase of active plate tectonics.
Six hundred million years ago, fever appeared in animals as a response to infections: the higher body temperatures optimized their immune systems. At the time, virtually all animal species were cold-blooded. They had to sit in warm patches of habitat for extended periods of time to achieve fever-range body temperatures. For Michael Logan, a Tupper Fellow at the Smithsonian Tropical Research Institute in Panama (STRI), pathogens may be the reason why warm-blooded creatures first emerged.
By keeping their bodies warm at all times, birds and mammals may be effectively priming their immune systems to withstand virulent pathogens [Credit: Michael Logan]
At first glance, cold-blooded creatures or 'ectotherms' seem to have it easy. Because they cannot regulate their body temperature internally, they spend 30 times less energy than warm-blooded creatures or 'endotherms' of the same size. So, while mammals and birds are constantly investing their calories in maintaining a high, stable body temperature, reptiles and amphibians can just search for a warm spot in their surrounding environment if they want to get cozy. But if ectothermy is so great, why did mammals and birds develop a different strategy that is so costly?
Over the years, scientists have proposed three different models for why endotherms evolved high, stable body temperatures. One claims that it aids physiological processes; another, that it helps animals maintain activity over longer periods of time; and the third, that it enables parents to take care of precocial offspring. However, none of these models have found strong support and the evolutionary history of endothermy remains somewhat of a mystery.
Although these various hypotheses may have some truth to them, for Logan, the trigger must have been something that profoundly impacted the ability of animals to survive and reproduce, otherwise endothermy would be too costly a strategy and would not be favored by natural selection. In a recent paper, published in the journal Ideas in Ecology and Evolution, he explains this theory.
The ability to mount a rapid fever response to a pathogen means warm-blooded creatures are not limited by the thermal variation in their habitats [Credit: Michael Logan]
"My hypothesis is that by keeping their bodies warm at nearly all times, mammals and birds effectively prime their immune systems to withstand virulent pathogens, and that this may be part of the reason the extremely costly strategy of endothermy evolved in the first place," Logan said.
In this context, endothermy may offer critical advantages over ectothermy. The ability to mount a rapid fever response to a pathogen means endotherms are not limited by the thermal variation in their habitats. Meanwhile, cold-blooded creatures depend on external sources of heat to reach fever-like temperatures. They are subject to fluctuations in environmental conditions, and in searching for the ideal microclimate required to initiate fever, they may struggle to forage or mate and may be exposed to predators.
"This hypothesis has emerged from recent discoveries in the fields of immunology and animal physiology, but we still need to rigorously test it with data and experiments," Logan said. "For example, my model predicts that species that maintain the warmest, most stable body temperatures (all else remaining equal) should also experience the highest frequency of disease outbreaks or the most virulent pathogens."
The first humans in North America arrived from Asia some time before 14,500 years ago. The next major stream of gene flow came about 5000 years ago, and is known to archaeologists as Paleo-Eskimos. About 800 years ago, the ancestors of the present-day Inuit and Yup'ik people replaced this population across the Arctic. By about 700 years ago, the archaeological evidence for the Paleo-Eskimo culture disappeared. Their genetic legacy in living populations has been contentious, with several genetic studies arguing that they made little contribution to later North Americans.
An ancient population of Arctic hunter-gatherers, known as Paleo-Eskimos, made a significant genetic contribution to populations living in Arctic North America today [Credit: Kerttu Majander, Design by Michelle O'Reilly]
In the current study, researchers generated genome-wide data from 48 ancient individuals and 93 modern individuals from Siberia, Alaska, the Aleutian Islands and Canada, and compared this with previously published data. The researchers used novel analysis methods to create a comprehensive model of population history that included many ancient and modern groups to determine how they might be related to each other.
"Our study is unique, not only in that it greatly expands the number of ancient genomes from this region, but because it is the first study to comprehensively describe all of these populations in one single coherent model," states Stephan Schiffels of the Max Planck Institute for the Science of Human History.
The researchers were able to show that a substantial proportion of the genetic heritage of all ancient and modern American Arctic and Chukotkan populations comes from Paleo-Eskimos. This includes people speaking Eskimo-Aleut languages, such as the Yup'ik, Inuit and Aleuts, and groups speaking Na-Dene languages, such as Athabaskan and Tlingit speakers, in Canada, Alaska, and the lower 48 states of the United States.
The excavation of the Middle Dorset individual from the Buchanan site on southeastern Victoria Island, Nunavut, Central Canadian Arctic [Credit: T. Max Friesen]
Based on the researchers' analysis, Paleo-Eskimos interbred with people with ancestry similar to more southern Native peoples shortly after their arrival to Alaska, between 5,000 and 4,000 years ago. The ancestors of Aleutian Islanders and Athabaskans derive their genetic heritage directly from the ancient mixture between these two groups.
The researchers also found that the ancestors of the Inuit and Yup'ik people crossed the Bering Strait at least three times: first as Paleo-Eskimos to Alaska, second as predecessors of the Old Bering Sea archaeological culture back to Chukotka, and third to Alaska again as bearers of the Thule culture. During their stay in Chukotka that likely lasted for more than 1000 years, Yupik and Inuit ancestors also admixed with local groups related to present-day Chukchi and local peoples from Kamchatka.
Paleo-Eskimo ancestry is particularly widespread today in Na-Dene language speakers, which includes Athabaskan and Tlingit communities from Alaska and northern Canada, the West Coast of the United States, and the southwest United States.
Attu Island, Aleutian Islands, Alaska [Credit: Jason Rogers]
"For the last seven years, there has been a debate about whether Paleo-Eskimos contributed genetically to people living in North America today; our study resolves this debate and furthermore supports the theory that Paleo-Eskimos spread Na-Dene languages," explains David Reich of Harvard Medical School and the Howard Hughes Medical Institute.
"One of the most striking case examples from our study is the ancient DNA we generated from the ancient Athabaskan site of Tochak McGrath in interior Alaska, where we worked in consultation with the local community to obtain data from three approximately seven hundred year old individuals. We found that these individuals, who lived after the time when the Paleo-Eskimo archaeological culture disappeared across North America, are well modeled as a mixture of the same two ancestry components as those found in Athabaskans today, and derived more than 40% of their ancestry from Paleo-Eskimos.
The researchers hope that the paper will provide an example of the value of genetic data, in the context of archaeological knowledge, to resolve long-standing questions.
"Determining what happened to this population was not possible from the archaeological record alone," explains Pavel Flegontov of the University of Ostrava. "By analyzing genetic data in concert with the archaeological data, we can meaningfully improve our understanding of the prehistory of peoples of this region. We faced challenging analytical problems due to the complex sequence of gene flows that have shaped ancestries of peoples on both sides of the Bering Strait. Reconstructing this sequence of events required new modelling approaches that we hope may be useful for solving similar problems in other regions of the world."
