Earthworms could help scientists ‘dig’ into past climates

A team of UK researchers believe earthworms could provide a window into past climates, allowing scientists to piece together the prevailing weather conditions thousands of years ago.

A laboratory study by researchers from the Universities of Reading and York has demonstrated that balls of calcium carbonate (small lumps of chalk-like material) excreted by the earthworm Lumbricus terrestris – commonly known as lobworms or nightcrawlers – maintain a memory of the temperature at which they were formed.

This, say the researchers, in an article in the journal Geochimica et Cosmochimica Acta, means that calcite granules, commonly recorded at sites of archaeological interest, have the potential to reveal important information about past climates which could be used to enhance and benchmark climate change models.

The study, which also involved English Heritage’s Centre for Archaeology, was funded by the Natural Environment Research Council (NERC).
Lead author Dr Emma Versteegh from the Department of Geography and Environmental Science at the University of Reading, said: “These chalk balls will allow us to reconstruct temperatures for specific time intervals in which they were formed. Reconstructions like this are interesting for archaeologists, because they give a climatic context to their finds. More importantly, climate proxies are the only means we have to study climate beyond the instrumental record, which only goes back about 150 year

“This knowledge about past climates is of vital importance for developing and benchmarking climate models that make predictions for the future. Many different proxies already exist, but no proxy is perfect, or is available in every location, so it is good to have many different ones.”

The proof of concept study involved keeping modern-day Lumbricus terrestris at different temperatures, then carrying out isotopic testing on the calcite granules excreted. This successfully demonstrated that the granules remembered the temperature at which they were formed.

Principal Investigator Professor Mark Hodson from the University of York’s Environment Department, and formerly of the University of Reading, said: “There are many conflicting theories about why earthworms produce calcite granules, but until now, the small lumps of chalk-like material found in earthworm poo have been seen as little more than a biological curiosity. However, our research shows they may well have an important role to play, offering a window into past climates.”

The researchers are now gathering samples from archaeological sites dating back thousands of years in preparation for isotopic testing.
Dr Stuart Black, from the University of Reading’s Department of Archaeology, added: “We believe this new method of delving into past climates has distinct advantages over other biological proxies. For example, we believe it will work for the full seasonal range of temperatures, whereas methods such as tree rings, do not “record” during winter. In addition, because the chalk balls are found in direct context with archaeological finds, they will reveal temperatures at the same location. At present, links are often attempted with climate proxies many hundreds or even thousands of miles away.”

A stepping-stone for oxygen on Earth

For most terrestrial life on Earth, oxygen is necessary for survival. But the planet’s atmosphere did not always contain this life-sustaining substance, and one of science’s greatest mysteries is how and when oxygenic photosynthesis-the process responsible for producing oxygen on Earth through the splitting of water molecules-first began. Now, a team led by geobiologists at the California Institute of Technology (Caltech) has found evidence of a precursor photosystem involving manganese that predates cyanobacteria, the first group of organisms to release oxygen into the environment via photosynthesis.

The findings, outlined in the June 24 early edition of the Proceedings of the National Academy of Sciences (PNAS), strongly support the idea that manganese oxidation-which, despite the name, is a chemical reaction that does not have to involve oxygen-provided an evolutionary stepping-stone for the development of water-oxidizing photosynthesis in cyanobacteria.

“Water-oxidizing or water-splitting photosynthesis was invented by cyanobacteria approximately 2.4 billion years ago and then borrowed by other groups of organisms thereafter,” explains Woodward Fischer, assistant professor of geobiology at Caltech and a coauthor of the study. “Algae borrowed this photosynthetic system from cyanobacteria, and plants are just a group of algae that took photosynthesis on land, so we think with this finding we’re looking at the inception of the molecular machinery that would give rise to oxygen.”

Photosynthesis is the process by which energy from the sun is used by plants and other organisms to split water and carbon dioxide molecules to make carbohydrates and oxygen. Manganese is required for water splitting to work, so when scientists began to wonder what evolutionary steps may have led up to an oxygenated atmosphere on Earth, they started to look for evidence of manganese-oxidizing photosynthesis prior to cyanobacteria. Since oxidation simply involves the transfer of electrons to increase the charge on an atom-and this can be accomplished using light or O2-it could have occurred before the rise of oxygen on this planet.

“Manganese plays an essential role in modern biological water splitting as a necessary catalyst in the process, so manganese-oxidizing photosynthesis makes sense as a potential transitional photosystem,” says Jena Johnson, a graduate student in Fischer’s laboratory at Caltech and lead author of the study.

To test the hypothesis that manganese-based photosynthesis occurred prior to the evolution of oxygenic cyanobacteria, the researchers examined drill cores (newly obtained by the Agouron Institute) from 2.415 billion-year-old South African marine sedimentary rocks with large deposits of manganese.

Manganese is soluble in seawater. Indeed, if there are no strong oxidants around to accept electrons from the manganese, it will remain aqueous, Fischer explains, but the second it is oxidized, or loses electrons, manganese precipitates, forming a solid that can become concentrated within seafloor sediments.

“Just the observation of these large enrichments-16 percent manganese in some samples-provided a strong implication that the manganese had been oxidized, but this required confirmation,” he says.

To prove that the manganese was originally part of the South African rock and not deposited there later by hydrothermal fluids or some other phenomena, Johnson and colleagues developed and employed techniques that allowed the team to assess the abundance and oxidation state of manganese-bearing minerals at a very tiny scale of 2 microns.

“And it’s warranted-these rocks are complicated at a micron scale!” Fischer says. “And yet, the rocks occupy hundreds of meters of stratigraphy across hundreds of square kilometers of ocean basin, so you need to be able to work between many scales-very detailed ones, but also across the whole deposit to understand the ancient environmental processes at work.”

Using these multiscale approaches, Johnson and colleagues demonstrated that the manganese was original to the rocks and first deposited in sediments as manganese oxides, and that manganese oxidation occurred over a broad swath of the ancient marine basin during the entire timescale captured by the drill cores.

“It’s really amazing to be able to use X-ray techniques to look back into the rock record and use the chemical observations on the microscale to shed light on some of the fundamental processes and mechanisms that occurred billions of years ago,” says Samuel Webb, coauthor on the paper and beam line scientist at the SLAC National Accelerator Laboratory at Stanford University, where many of the study’s experiments took place. “Questions regarding the evolution of the photosynthetic pathway and the subsequent rise of oxygen in the atmosphere are critical for understanding not only the history of our own planet, but also the basics of how biology has perfected the process of photosynthesis.”

Once the team confirmed that the manganese had been deposited as an oxide phase when the rock was first forming, they checked to see if these manganese oxides were actually formed before water-splitting photosynthesis or if they formed after as a result of reactions with oxygen. They used two different techniques to check whether oxygen was present. It was not-proving that water-splitting photosynthesis had not yet evolved at that point in time. The manganese in the deposits had indeed been oxidized and deposited before the appearance of water-splitting cyanobacteria. This implies, the researchers say, that manganese-oxidizing photosynthesis was a stepping-stone for oxygen-producing, water-splitting photosynthesis.

“I think that there will be a number of additional experiments that people will now attempt to try and reverse engineer a manganese photosynthetic photosystem or cell,” Fischer says. “Once you know that this happened, it all of a sudden gives you reason to take more seriously an experimental program aimed at asking, ‘Can we make a photosystem that’s able to oxidize manganese but doesn’t then go on to split water? How does it behave, and what is its chemistry?’ Even though we know what modern water splitting is and what it looks like, we still don’t know exactly how it works. There is a still a major discovery to be made to find out exactly how the catalysis works, and now knowing where this machinery comes from may open new perspectives into its function-an understanding that could help target technologies for energy production from artificial photosynthesis. ”

Next up in Fischer’s lab, Johnson plans to work with others to try and mutate a cyanobacteria to “go backwards” and perform manganese-oxidizing photosynthesis. The team also plans to investigate a set of rocks from western Australia that are similar in age to the samples used in the current study and may also contain beds of manganese. If their current study results are truly an indication of manganese-oxidizing photosynthesis, they say, there should be evidence of the same processes in other parts of the world.

“Oxygen is the backdrop on which this story is playing out on, but really, this is a tale of the evolution of this very intense metabolism that happened once-an evolutionary singularity that transformed the planet,” Fischer says. “We’ve provided insight into how the evolution of one of these remarkable molecular machines led up to the oxidation of our planet’s atmosphere, and now we’re going to follow up on all angles of our findings.”

Irish chronicles reveal links between cold weather and volcanic eruptions

Medieval chronicles have given an international group of researchers a glimpse into the past to assess how historical volcanic eruptions affected the weather in Ireland up to 1500 years ago.

By critically assessing over 40,000 written entries in the Irish Annals and comparing them with measurements taken from ice cores, the researchers successfully linked the climatic aftermath of volcanic eruptions to extreme cold weather events in Ireland over a 1200-year period from 431 to 1649.

Their study, which has been published today, 6 June, in IOP Publishing’s journal Environmental Research Letters, showed that over this timescale up to 48 explosive volcanic eruptions could be identified in the Greenland Ice Sheet Project (GISP2) ice-core, which records the deposition of volcanic sulfate in annual layers of ice.

Of these 48 volcanic events, 38 were associated, closely in time, with 37 extreme cold events, which were identified by systematically examining written entries in the Irish Annals and picking out directly observed meteorological phenomena and conditions, such as heavy snowfall and frost, prolonged ice covering lakes and rivers, and contemporary descriptions of abnormally cold weather.

Lead author of the study, Dr Francis Ludlow, from the Harvard University Center for the Environment and Department of History, said: “It’s clear that the scribes of the Irish Annals were diligent reporters of severe cold weather, most probably because of the negative impacts this had on society and the biosphere.

“Our major result is that explosive volcanic eruptions are strongly, and persistently, implicated in the occurrence of cold weather events over this long timescale in Ireland. In their severity, these events are quite rare for the country’s mild maritime climate.”

Through the injection of sulphur dioxide gas into the stratosphere, volcanic eruptions can play a significant role in the regulation of the Earth’s climate. Sulphur dioxide gas is converted into sulphate aerosol particles after eruptions which reflect incoming sunlight and result in an overall temporary cooling of the Earth’s surface.

Whilst the global effects of recent eruptions are quite well-known, such as the Mount Pinatubo eruption almost 22 years ago (15 June 1991), less is known about their effects on climate before the beginning of instrumental weather recording, or their effects on regional scales; the Irish Annals provided an opportunity to explore both of these issues.

The Irish Annals contain over one million written words and around 40,000 distinct written entries, detailing major historical events on an annual basis, and providing both systematic and sustained reporting of meteorological extremes.

The dating and reliability of the Annals can be gauged by comparing reported events to those which are independently known, such as solar and lunar eclipses.

“With a few honourable exceptions, the Irish record of extreme events has only been used anecdotally, rather than systematically surveyed and exploited for the study of the climate history of Ireland and the North Atlantic, and so the richness of the record has been largely unrecognized,” continued Dr Ludlow.

Although the effect of big eruptions on the climate in summer is largely to cause cooling, during the winter, low-latitude eruptions in the tropics have instead been known to warm large parts of the northern hemisphere as they cause a strengthening of the westerly winds that brings, for example, warmer oceanic air to Europe; however, this study identified several instances when low-latitude eruptions appeared to correspond to extreme cold winters in Ireland.

One example is the 1600 eruption in Peru of Huaynaputina, which the researchers found, against expectations, to be associated with extreme cold winter weather in Ireland in the following years.

“The possibility that tropical eruptions may result in severe winter cooling for Ireland highlights the considerable complexity of the volcano-climate system in terms of the regional expression of the response of climate to volcanic disturbances.

“It is on the regional scale that we need to refine our understanding of this relationship as ultimately, it is on this scale that individuals and societies plan for extreme weather,” continued Dr Ludlow.

Volcanoes cause climate gas concentrations to vary

MIPAS data confirm the correlation between high sulfur dioxide concentrations (yellow-red) and high-reaching volcano eruptions (triangles). -  (Figure: KIT/M. Höpfner)
MIPAS data confirm the correlation between high sulfur dioxide concentrations (yellow-red) and high-reaching volcano eruptions (triangles). – (Figure: KIT/M. Höpfner)

Trace gases and aerosols are major factors influencing the climate. With the help of highly complex installations, such as MIPAS on board of the ENVISAT satellite, researchers try to better understand the processes in the upper atmosphere. Now, Karlsruhe Institute of Technology presents the most comprehensive overview of sulfur dioxide measurements in the journal of Atmospheric Chemistry and Physics (doi:10.5194/acpd-13-12389-2013).

“Sulfur compounds up to 30 km altitude may have a cooling effect,” Michael Höpfner, the KIT scientist responsible for the study, says. For example, sulfur dioxide (SO2) and water vapor react to sulfuric acid that forms small droplets, called aerosols, that reflect solar radiation back into universe. “To estimate such effects with computer models, however, the required measurement data have been lacking so far.” MIPAS infrared spectrometer measurements, however, produced a rather comprehensive set of data on the distribution and development of sulfur dioxide over a period of ten years.

Based on these results, major contributions of the sulfur budget in the stratosphere can be analyzed directly. Among others, carbonyl sulfide (COS) gas produced by organisms ascends from the oceans, disintegrates at altitudes higher than 25 km, and provides for a basic concentration of sulfur dioxide. The increase in the stratospheric aerosol concentration observed in the past years is caused mainly by sulfur dioxide from a number of volcano eruptions. “Variation of the concentration is mainly due to volcanoes,” Höpfner explains. Devastating volcano eruptions, such as those of the Pinatubo in 1991 and Tambora in 1815, had big a big effect on the climate. The present study also shows that smaller eruptions in the past ten years produced a measurable effect on sulfur dioxide concentration at altitudes between 20 and 30 km. “We can now exclude that anthropogenic sources, e.g. power plants in Asia, make a relevant contribution at this height,” Höpfner says.

“The new measurement data help improve consideration of sulfur-containing substances in atmosphere models,” Höpfner explains. “This is also important for discussing the risks and opportunities of climate engineering in a scientifically serious manner.”

MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) was one of the main instruments on board of the European environmental satellite ENVISAT that supplied data from 2002 to 2012. MIPAS was designed by the KIT Institute of Meteorology and Climate Research. All around the clock, the instrument measured temperature and more than 30 atmospheric trace gases. It recorded more than 75 million infrared spectra. KIT researchers, together with colleagues from Forschungszentrum Jülich, have now developed the MIPAS successor GLORIA that may be the basis of a future satellite instrument for climate research.

Comprehensive analysis of impact spherules supports theory of cosmic impact 12,800 years ago

This is UCSB Earth Sciences professor emeritus James Kennett. -  Courtesy photo
This is UCSB Earth Sciences professor emeritus James Kennett. – Courtesy photo

About 12,800 years ago when the Earth was warming and emerging from the last ice age, a dramatic and anomalous event occurred that abruptly reversed climatic conditions back to near-glacial state. According to James Kennett, UC Santa Barbara emeritus professor in earth sciences, this climate switch fundamentally — and remarkably — occurred in only one year, heralding the onset of the Younger Dryas cool episode.

The cause of this cooling has been much debated, especially because it closely coincided with the abrupt extinction of the majority of the large animals then inhabiting the Americas, as well as the disappearance of the prehistoric Clovis culture, known for its big game hunting.

“What then did cause the extinction of most of these big animals, including mammoths, mastodons, giant ground sloths, American camel and horse, and saber- toothed cats?” asked Kennett, pointing to Charles Darwin’s 1845 assessment of the significance of climate change. “Did these extinctions result from human overkill, climatic change or some catastrophic event?” The long debate that has followed, Kennett noted, has recently been stimulated by a growing body of evidence in support of a theory that a major cosmic impact event was involved, a theory proposed by the scientific team that includes Kennett himself.

Now, in one of the most comprehensive related investigations ever, the group has documented a wide distribution of microspherules widely distributed in a layer over 50 million square kilometers on four continents, including North America, including Arlington Canyon on Santa Rosa Island in the Channel Islands. This layer — the Younger Dryas Boundary (YDB) layer — also contains peak abundances of other exotic materials, including nanodiamonds and other unusual forms of carbon such as fullerenes, as well as melt-glass and iridium. This new evidence in support of the cosmic impact theory appeared recently in a paper in the Proceedings of the National Academy of the Sciences.

This cosmic impact, said Kennett, caused major environmental degradation over wide areas through numerous processes that include continent-wide wildfires and a major increase in atmospheric dust load that blocked the sun long enough to cause starvation of larger animals.

Investigating 18 sites across North America, Europe and the Middle East, Kennett and 28 colleagues from 24 institutions analyzed the spherules, tiny spheres formed by the high temperature melting of rocks and soils that then cooled or quenched rapidly in the atmosphere. The process results from enormous heat and pressures in blasts generated by the cosmic impact, somewhat similar to those produced during atomic explosions, Kennett explained.

But spherules do not form from cosmic collisions alone. Volcanic activity, lightning strikes, and coal seam fires all can create the tiny spheres. So to differentiate between impact spherules and those formed by other processes, the research team utilized scanning electron microscopy and energy dispersive spectrometry on nearly 700 spherule samples collected from the YDB layer. The YDB layer also corresponds with the end of the Clovis age, and is commonly associated with other features such as an overlying “black mat” — a thin, dark carbon-rich sedimentary layer — as well as the youngest known Clovis archeological material and megafaunal remains, and abundant charcoal that indicates massive biomass burning resulting from impact.

The results, according to Kennett, are compelling. Examinations of the YDB spherules revealed that while they are consistent with the type of sediment found on the surface of the earth in their areas at the time of impact, they are geochemically dissimilar from volcanic materials. Tests on their remanent magnetism — the remaining magnetism after the removal of an electric or magnetic influence — also demonstrated that the spherules could not have formed naturally during lightning strikes.

“Because requisite formation temperatures for the impact spherules are greater than 2,200 degrees Celsius, this finding precludes all but a high temperature cosmic impact event as a natural formation mechanism for melted silica and other minerals,” Kennett explained. Experiments by the group have for the first time demonstrated that silica-rich spherules can also form through high temperature incineration of plants, such as oaks, pines, and reeds, because these are known to contain biologically formed silica.

Additionally, according to the study, the surface textures of these spherules are consistent with high temperatures and high-velocity impacts, and they are often fused to other spherules. An estimated 10 million metric tons of impact spherules were deposited across nine countries in the four continents studied. However, the true breadth of the YDB strewnfield is unknown, indicating an impact of major proportions.

“Based on geochemical measurements and morphological observations, this paper offers compelling evidence to reject alternate hypotheses that YDB spherules formed by volcanic or human activity; from the ongoing natural accumulation of space dust; lightning strikes; or by slow geochemical accumulation in sediments,” said Kennett.

“This evidence continues to point to a major cosmic impact as the primary cause for the tragic loss of nearly all of the remarkable American large animals that had survived the stresses of many ice age periods only to be knocked out quite recently by this catastrophic event.”

Cracking the ice code

UWM geosciences professor John Isbell (left) and postdoctoral researcher Erik Gulbranson, University of Wisconsin, Milwaukee, look over some of the many samples they have brought back from Antarctica. The two are part of an international team of scientists investigating the last extreme climate shift on Earth, which occurred in the late Paleozoic Era. -  Troye Fox
UWM geosciences professor John Isbell (left) and postdoctoral researcher Erik Gulbranson, University of Wisconsin, Milwaukee, look over some of the many samples they have brought back from Antarctica. The two are part of an international team of scientists investigating the last extreme climate shift on Earth, which occurred in the late Paleozoic Era. – Troye Fox

What happened the last time a vegetated Earth shifted from an extremely cold climate to desert-like conditions? And what does it tell us about climate change today?

John Isbell is on a quest to coax that information from the geology of the southernmost portions of the Earth. It won’t be easy, because the last transition from “icehouse to greenhouse” occurred between 335 and 290 million years ago.

An expert in glaciation from the late Paleozoic Era, Isbell is challenging many assumptions about the way drastic climate change naturally unfolds. The research helps form the all-important baseline needed to predict what the added effects of human activity will bring.

Starting from ‘deep freeze’

In the late Paleozoic, the modern continents were fused together into two huge land masses, with what is now the Southern Hemisphere, including Antarctica, called Gondwana.

During the span of more than 60 million years, Gondwana shifted from a state of deep freeze into one so hot and dry it supported the appearance of reptiles. The change, however, didn’t happen uniformly, Isbell says.

In fact, his research has shaken the common belief that Gondwana was covered by one massive sheet of ice which gradually and steadily melted away as conditions warmed.

Isbell has found that at least 22 individual ice sheets were located in various places over the region. And the state of glaciation during the long warming period was marked by dramatic swings in temperature and atmospheric carbon dioxide (CO2) levels.

“There appears to be a direct association between low CO2 levels and glaciation,” he says. “A lot of the changes in greenhouse gases and in a shrinking ice volume then are similar to what we’re seeing today.”

When the ice finally started disappearing, he says, it did so in the polar regions first and lingered in other parts of Gondwana with higher elevations. He attributes that to different conditions across Gondwana, such as mountain-building events, which would have preserved glaciers longer.

All about the carbon

To get an accurate picture of the range of conditions in the late Paleozoic, Isbell has traveled to Antarctica 16 times and has joined colleagues from around the world as part of an interdisciplinary team funded by the National Science Foundation. They have regularly gone to places where no one has ever walked on the rocks before.

One of his colleagues is paleoecologist Erik Gulbranson, who studies plant communities from the tail end of the Paleozoic and how they evolved in concert with the climatic changes. The information contained in fossil soil and plants, he says, can reveal a lot about carbon cycling, which is so central for applying the work to climate change today.

Documenting the particulars of how the carbon cycle behaved so long ago will allow them to answer questions like, ‘What was the main force behind glaciation during the late Paleozoic? Was it mountain-building or climate change?’

Another characteristic of the late Paleozoic shift is that once the climate warmed significantly and atmospheric CO2 levels soared, the Earth’s climate remained hot and dry for another 200 million years.

“These natural cycles are very long, and that’s an important difference with what we’re seeing with the contemporary global climate change,” says Gulbranson. “Today, we’re seeing change in greenhouse gas concentrations of CO2 on the order of centuries and decades.”

Ancient trees and soil

In order to explain today’s accelerated warming, Gulbranson’s research illustrates that glaciers alone don’t tell the whole story.

Many environmental factors leave an imprint on the carbon contained in tree trunks from this period. One of the things Gulbranson hypothesizes from his research in Antarctica is that an increase in deciduous trees occurred in higher latitudes during the late Paleozoic, driven by higher temperatures.

What he doesn’t yet know is what the net effect was on the carbon cycle.

While trees soak in CO2 and give off oxygen, there are other environmental processes to consider, says Gulbranson. For example, CO2 emissions also come from soil as microbes speed up their consumption of organic matter with rising temperatures.

“The high latitudes today contain the largest amount of carbon locked up as organic material and permafrost soils on Earth today,” he says. “It actually exceeds the amount of carbon you can measure in the rain forests. So what happens to that stockpile of carbon when you warm it and grow a forest over it is completely unknown.”

Another unknown is whether the Northern Hemisphere during this time was also glaciated and warming. The pair are about to find out. With UWM backing, they will do field work in northeastern Russia this summer to study glacial deposits from the late Paleozoic.

The two scientists’ work is complementary. Dating the rock is essential to pinpointing the rate of change in the carbon cycle, which would be the warning signal we could use today to indicate that nature is becoming dangerously unbalanced.

“If we figure out what happened with the glaciers,” says Isbell, “and add it to what we know about other conditions – we will be able to unlock the answers to climate change.”

Earth’s iron core is surprisingly weak, Stanford researchers say

The massive ball of iron sitting at the center of Earth is not quite as “rock-solid” as has been thought, say two Stanford mineral physicists. By conducting experiments that simulate the immense pressures deep in the planet’s interior, the researchers determined that iron in Earth’s inner core is only about 40 percent as strong as previous studies estimated.

This is the first time scientists have been able to experimentally measure the effect of such intense pressure – as high as 3 million times the pressure Earth’s atmosphere exerts at sea level – in a laboratory. A paper presenting the results of their study is available online in Nature Geoscience.

“The strength of iron under these extreme pressures is startlingly weak,” said Arianna Gleason, a postdoctoral researcher in the department of Geological and Environmental Sciences, and lead author of the paper. Wendy Mao, an assistant professor in the department, is the co-author.

“This strength measurement can help us understand how the core deforms over long time scales, which influences how we think about Earth’s evolution and planetary evolution in general,” Gleason said.

Until now, almost all of what is known about Earth’s inner core came from studies tracking seismic waves as they travel from the surface of the planet through the interior. Those studies have shown that the travel time through the inner core isn’t the same in every direction, indicating that the inner core itself is not uniform. Over time and subjected to great pressure, the core has developed a sort of fabric as grains of iron elongate and align lengthwise in parallel formations.

The ease and speed with which iron grains in the inner core can deform and align would have influenced the evolution of the early Earth and development of the geomagnetic field. The field is generated by the circulation of liquid iron in the outer core around the solid inner core and shields Earth from the full intensity of solar radiation. Without the geomagnetic field, life – at least as we know it – would not be possible on Earth.

“The development of the inner core would certainly have some effect on the geomagnetic field, but just what effect and the magnitude of the effect, we can’t say,” said Mao. “That is very speculative.”

Gleason and Mao conducted their experiments using a diamond anvil cell – a device that can exert immense pressure on tiny samples clenched between two diamonds. They subjected minute amounts of pure iron to pressures between 200 and 300 gigapascals (equivalent to the pressure of 2 million to 3 million Earth atmospheres). Previous experimental studies were conducted in the range of only 10 gigapascals.

“We really pushed the limit here in terms of experimental conditions,” Gleason said. “Pioneering advancements in pressure-generation techniques and improvements in detector sensitivity, for example, used at large X-ray synchrotron facilities, such as Argonne National Lab, have allowed us to make these new measurements.”

In addition to intense pressures, the inner core also has extreme temperatures. The boundary between the inner and outer core has temperatures comparable to the surface of the sun. Simultaneously simulating both the pressure and temperature at the inner core isn’t yet possible in the laboratory, though Gleason and Mao are working on that for future studies. (For this study, Gleason mathematically extrapolated from their pressure data to factor in the effect of temperature.)

Gleason and Mao expect their findings will help other researchers set more realistic variables for conducting their own experiments.

“People modeling the inner core haven’t had many experimental constraints, because it’s so difficult to make measurements under those conditions,” Mao said. “There really weren’t constraints on how strong the core was, so this is really a fundamental new constraint.”

Ancient trash heaps gave rise to Everglades tree islands

Garbage mounds left by prehistoric humans might have driven the formation of many of the Florida Everglades’ tree islands, distinctive havens of exceptional ecological richness in the sprawling marsh that are today threatened by human development.

Tree islands are patches of relatively high and dry ground that dot the marshes of the Everglades. Typically a meter (3.3 feet) or so high, many of them are elevated enough to allow trees to grow. They provide a nesting site for alligators and a refuge for birds, panthers, and other wildlife.

Scientists have thought for many years that the so-called fixed tree islands (a larger type of tree island frequently found in the Everglades’ main channel, Shark River Slough) developed on protrusions from the rocky layer of a mineral called carbonate that sits beneath the marsh. Now, new research indicates that the real trigger for island development might have been middens, or trash piles left behind from human settlements that date to about 5,000 years ago.

These middens, a mixture of bones, food discards, charcoal, and human artifacts (such as clay pots and shell tools), would have provided an elevated area, drier than the surrounding marsh, allowing trees and other vegetation to grow. Bones also leaked phosphorus, a nutrient for plants that is otherwise scarce in the Everglades.

“This goes to show that human disturbance in the environment doesn’t always have a negative consequence,” says Gail Chmura, a paleoecologist at McGill University in Montreal, Canada, and one of the authors of the study.

Chmura will be presenting her research tomorrow, Tuesday 22 March, at the American Geophysical Union’s Chapman Conference on Climates, Past Landscapes, and Civilizations. About 95 scientists have converged on Santa Fe this week to discuss the latest research findings from archeology, paleoclimatology, paleoecology, and other fields that reveal how changes in regional and global climate have impacted the development and fates of societies.

In a previous scientific investigation of tree islands, Margo Schwadron, an archeologist with the National Park Service, cut through the elevated bedrock at the base of two islands and discovered that it was actually a so-called “perched carbonate layer,” because there was more soil and a midden below. Later, a team including Chmura’s graduate student Maria-Theresia Graf performed additional excavations in South Florida and found more of the perched carbonate layers.

Chemical analysis of samples of these curious perched layers revealed that they are made up partially of carbonates that had dissolved from the bedrock below, Chmura says. The layer also contains phosphorus from dissolved bones, she adds. Her team concluded that trees are key to the formation of this layer: During South Florida’s dry season, their roots draw in large quantities of ground water but allow the phosphates and carbonates dissolved in it to seep out and coalesce into the stone-like layer.

The perched carbonate plays a key role in letting tree islands rebound after fires: because it does not burn, it protects the underlying soil, and it maintains the islands’ elevation, allowing vegetation to regrow after the fire. Humans are now threatening the existence of tree islands, by cutting down trees (whose roots keep the perched layer in place) and artificially maintaining high water levels year-round in some water control systems, which could cause the layer to dissolve.

Chmura’s team now wants to explore exactly when trees started growing on the tree islands.

Glacial melting may release pollutants in the environment

Pollutants from melting glaciers may help explain an increase in persistent organic pollutants in certain lakes since the 1990s, despite decreased used of pesticides. -  Wikimedia Commons
Pollutants from melting glaciers may help explain an increase in persistent organic pollutants in certain lakes since the 1990s, despite decreased used of pesticides. – Wikimedia Commons

Those pristine-looking Alpine glaciers now melting as global warming sets in may explain the mysterious increase in persistent organic pollutants in sediment from certain lakes since the 1990s, despite decreased use of those compounds in pesticides, electric equipment, paints and other products. That’s the conclusion of a new study, scheduled for the Nov. 1 issue of ACS’ Environmental Science & Technology, a semi-monthly journal.

In the study, Christian Bogdal and colleagues focused on organic pollutants in sediment from a model body of water — glacier-fed Lake Oberaar in the Bernese Alps, Switzerland — testing for the persistent organic pollutants, including dioxins, PCBs, organochlorine pesticides and synthetic musk fragrances. They found that while contamination decreased to low levels in the 1980s and 1990s due to tougher regulations and improvements in products, since the late 1990s flow of all of these pollutants into the lake has increased sharply. Currently, the flow of organochlorines into the lake is similar to or even higher than in the 1960s and 1970s, the report states.

The study attributed the most recent spike in the flow of pollutants into Lake Oberaar to the accelerated release of organic chemicals from melting Alpine glaciers, where contaminants were deposited earlier and preserved over decades. “Considering ongoing global warming and accelerated massive glacial melting predicted for the future, our study indicates the potential for environmental impacts due to pollutants delivered into pristine mountainous areas,” Bogdal said.