Ice loss from the East Antarctic Ice Sheet during late Pleistocene interglacials David J. Wilson, Rachel A. Bertram, Emma F. Needham, Tina van de Flierdt, Kevin J. Welsh, Robert M. McKay, Anannya Mazumder, Christina R. Riesselman, Francisco J. Jiminez-Espejo, Carlota Escutia Summarized by Time Scavengers collaborator Adriane Lam
Brief Summary: Today, sea level rise due to increasing global average temperatures is a huge threat to low-lying, coastal, and island communities. Sea level is rising, in part, from ice that is melting on Antarctica and Greenland. To understand how much sea level may rise in the near future, scientists look to the geologic past, when global temperatures were much warmer than today or close to the temperatures predicted for the coming decades. In this study, scientists looked at how much ice was lost from the Wilkes Subglacial Basin of East Antarctica during a time when global average temperatures were about 2 degrees Celsius warmer than pre-industrial values. They find that during these warmer periods, called interglacials, there was significant ice that melted from East Antarctica, and contributed to sea level rises. Thus, in the future, the ice melting from East Antarctica will contribute more to sea level rise than we previously thought.
Data used and Methods: Sediment from a deep-sea core drilled from the continental margin of East Antarctica was used in this study (Figure 1). From this sediment core, the authors analyzed the different types of sediment contained within the core through time. From the changes in sediments, the scientists could tell how much erosion was occurring. They also looked at the neodymium (Nd) isotopes from the sediments. Nd isotopes are a good way to also trace where the sediments in the core were coming from, so the scientists could determine not only how much erosion was taking place within East Antarctica, but where the eroded sediment was coming from. Increased erosion and a shift in the Nd isotope records indicate increased glacial melt and ice retreat on East Antarctica, thus the authors could tell through geologic time when and approximately how much the ice melted.
Results: Over the past 800,000 years, Earth’s climate has oscillated between cooler (glacial) and warmer (interglacial) periods (read more about this on our CO2 page). During some interglacial periods (times when the climate was warmer), the scientists found that the East Antarctic Ice Sheet began to erode the rock on which it sits and melted significantly. This led to increased sea levels within a world that was less warm than today.
Why is this study important? This study places new approximations on how much melting from East Antarctica could occur in a warming world, and how much that could raise sea level. Climate scientists think that if all the ice on East Antarctica were to melt, it would lead to approximately 53 meters of sea level rise globally! With the data from this study, it will provide new constraints on melting ice in a warming world, which will be incorporated into climate models of the future climate. This data will be given to policymakers to help us best prepare and mitigate the consequences of climate change.
Citation: Wilson, D. J., Bertram, R. A., Needham, E. F., van de Flierdt, T., Welsh, K. J., McKay, R. M., Mazumder, A., Riesselman, C. R., Jimenez-Espejo, F. J., and Escutia, C., 2019. Ice loss from the East Antarctic Ice Sheet during late Pleistocene interglacials. Nature 561, 383-386.
Permian metabolic bone disease revealed by microCT: Paget’s disease-like pathology in vertebrae of an early amniote Yara Haridy, Florian Witzmann, Patrick Asbach, Robert R. Reisz Summarized by Time Scavenger collaborator Jen Bauer
Brief Summary: This study examined bone remodeling (how the bone fixes itself after disease or other events) in an amniote (animals such as birds, reptiles, and mammals) from the early Permian (289 million years ago). Through detailed measurements and 3D internal and external modeling of the bone the authors determined that this animal suffered from a metabolic bone disease similar to Paget’s disease in humans. This is the oldest evidence of viral infection in the fossil record!
What data were used? The authors were exploring two fused (pathological or abnormal) and one normal vertebra. Vertebrae are the interlocking bones that make up your spinal column. They were able to identify both specimens as being caudal vertebraes (vertebrae of the tail area) of a varanopid animal. For comparison, the authors also examined several other non-pathological caudal vertebrae of a similar animal for comparison to this abnormal specimen.
Varanopids are an extinct group of amniotes (animals that have a membrane around their embryos) that looked similar to extant (still alive) monitor lizards. The veranopids were alive from the late Carboniferous to the late Middle Permian (~300-260 million years ago).
Methods: Measurements of the specimens were done using ImageJ, a freely available imaging editing program that can be used for a variety of projects. The idea was to measure different thickness of the bones. There is bone repair due to the disease and the author’s were quantifying the difference in the diseased bone compared to the thicknesses of normal (non-diseased) bones. Specimens were also CT scanned at the Museum für Naturkunde Berlin and the models were visualized and analyzed in Volume Graphics Studio MAX 2.2. Computed Tomography (CT) allows for scientists to look inside the bones without cutting them into pieces, making it a non-destructive visualization technique. This is particularly helpful for looking at any internal bone structure and any possible abnormalities in the external or internal structure.
Results:The pathological (diseased) specimen is two vertebral centra completely fused together, with no trace of a previous suture between the bones. The internal bone structure is slightly different. The notochordal canal (where the notochord resides) is uniform where there is some tapering the non-pathological specimens. The micro-CT scans reveal the outer cortex of the vertebrae has been dramatically altered through bone remodeling and growth causing features to be thickened and misshapen.
Why is this study important? The oldest recorded case of Paget disease of bone (PBD)-like alteration was in a Late Jurassic (~150 million years ago) vertebrate of a dinosaur, so this new find pushes the interpretation back to the Permian (~290 million years ago) – a shift of 140 million years back! The other major finding is about how this disease affects animals. Certain organisms are susceptible to certain diseases more than others. This bone disease has been found in primates (including humans), extant (living) dogs, lizards and snakes, and a dinosaur. The new finding in a varanopid furthers the spread across the tree of life, meaning that the disease must have evolved in early amniotes before the split between the split of synapsids (mammals) and diapsids (reptiles and birds).
Citation: Haridy Y, Witzmann F, Asbach P, Reisz RR (2019) Permian metabolic bone disease revealed by microCT: Paget’s disease-like pathology in vertebrae of an early amniote. PLoS ONE 14(8): e0219662. https://doi.org/10.1371/journal.pone.0219662
A new stemmed echinoderm from the Furongian of China and the origin of Glyptocystitida (Blastozoa, Echinodermata) S. Zamora, C.D. Sumrall, X-J. Zhu, and B. Lefebvre Summarized by Time Scavengers contributor, Sarah Sheffield
What data were used? A single, beautifully preserved echinoderm (relatives of sea stars and sea urchins) fossil from South China, named Sanducystis sinensis. Rhombiferans are extinct types of echinoderms with diamond shaped plates.
Methods: The new rhombiferan fossil was examined for all preserved features on its body; these features were ‘coded’ as characters for an evolutionary analysis. An example of a character: Does this have a stem? Yes=0; No=1. These characters were also used to code multiple other species of rhombiferan echinoderms. The reason for this was to figure out to what Sanducystis sinensis was most closely related. Computer programs, like PAUP*, take all of the characters coded and determine evolutionary relationships, based on the shared similarities between the species used in the analysis.
Results:Sanducystis sinensis falls within a large group of rhombiferan echinoderms called “Glyptocystitida” (similar to how humans are a large group of mammals). It’s an important find, as its place within the evolutionary tree of life is representative of a type of transitional fossil between a group of early rhombiferans that lack specialized breathing apparati and a group of more advanced, or derived, rhombiferans.
Why is this study important? This study paints a more complete story of how rhombiferans evolved through the Cambrian. It was not clear how the transition from rhombiferans without specialized breathing apparati gave rise to the more derived forms that we saw after the late Cambrian. This new find, Sanducystis sinensis, helps us to understand how that transition happened.
Big picture: Rocks from the late Cambrian (~500-480 million years ago) are very rare worldwide; this, of course, means that there are also very few fossils from this time as well. The late Cambrian is a very important time in Earth’s history, however, so finding fossils preserved from this time is critical towards understanding the evolution of life. Fossil finds, such as Sanducystis sinensis, have the potential to completely change what we currently know about how and when different groups of organisms on Earth evolved.
Microplastics alter feeding selectivity and faecal density in the copepod, Calanus helgolandicus
Rachel L. Coppock, Tamara S. Galloway, Matthew Cole, Elaine S. Fileman, Ana M. Queirós, & Penelope K. Lindeque
Summarized by Adriane Lam
The Problem: There is a growing body of research that shows that microplastics, tiny (1um-5 mm) pieces of plastics, have made their way into the deepest reaches of our oceans and are being ingested by marine life. Microplastics ingested by animals have been shown to cause adverse health effects to them, but as consumers of marine animals, these same microplastics are making their way into our diets. As yet, we do not know the exact ways in which microplastics can affect human health on longer time scales.
Zooplankton, which are small animals and protists that float in the water column and feed on primary-producing phytoplankton, are an important link between phytoplankton and other, larger animals. Zooplankton make up the base of the food chain, and are the main food source of marine mammals such as blue whales.
One type of zooplankton is especially common in our oceans today. Copepods are marine crustaceans that are found in nearly every freshwater and saltwater habitat. In addition to being an important food source, copepod poop is an important part of the biological pump. In other words, these animals’ poop transports atmospheric carbon dioxide (which is trapped in organic matter, or fixed carbon) to the seafloor, where it is stored in seafloor sediments. The poop also provides important nutrients to other animals that live within or on top of these sediments. Copepods have been shown to ingest microplastics in the wild. The ingestion of microplastics by copepods may alter the way in which these animals select their food. And of course, if microplastics are being ingested, they are also being exported to the seafloor in fecal pellets. This study was designed to look at how microplastics alter how copepods choose their food and how the ingested plastic materials affect the sinking rate of copepod poop.
Methods: In this study, the scientists grew three species of microalgae (all that copepods like to feast on) in the lab and spiked it with different types of microplastics. The microplastics included things such as nylon, which is commonly found in clothing, especially active wear, and polyethylene, which is the most commonly-used plastic in the world (it is used to make shopping bags, shampoo bottles, and toys, to name a few uses).
The microalgae with microplastics was then fed to the copepods back in the lab, where the amount of microplastics ingested. The fecal pellets from the copepods were then collected and rinsed over a screen. To determine if microplastics contained in the poop affected the sinking rate of the pellets, the scientists dropped the pellets into cylinders filled with filtered seawater. They marked where the pellet was in the cylinder every 40 mm. To determine how different each pellet sank with microplastics, the scientists also measured the rate at which copepod poop without microplastics fell through the water column. When the poop reached the bottom of the cylinders, they were taken out and examined under a microscope. This way, the scientists could count the number of plastic pieces in each pellet.
Results: The scientists found that copepods preferentially liked to eat microplastics in a smaller size range (10-20 um), with a preference for the polyethylene over nylon fibers. When the copepods were exposed to microplastics, they preferentially did not eat as much algae. In addition, the copepods shifted their preference for one species of algae over others. Nylon fibers impeded ingestion of algae that was a similar size and shape to the microplastics. The scientists think the copepods associated algae of similar size and shape with microplastics, and thus avoided eating that algae species in an attempt to avoid plastic consumption.
The study confirmed that fecal pellets that contained both polyethylene and nylon particles were slower to sink through the water column. There was a difference in sinking rates between poop that contained more polyethylene, a denser microplastic, compared to nylon, a less dense material.
Why is this study important? This study is one of several that highlight the ways in which plastics are negatively affecting our food chain in the marine realm. The reduced sinking rate of fecal pellets may also affect the rate at which carbon dioxde, a major greenhouse gas, can be removed from the atmosphere through photosynthesizing algae who are then eaten by zooplankton. If fecal pellets are left to float for longer, there is also a higher potential of the microplastics being re-ingested by other zooplankton through coprophagy (ingestion of fecal pellets). On long and short timescales, the decreased export of poop and fixed carbon dioxide to the seafloor may have large consequences, as plastic within poop could keep more carbon from being exported and stored on the seafloor.
Citation: Coppock, R. L., Galloway, T. S., Cole, M., Fileman, E. S., Queirós, A. M., and Lindeque, P. K., 2019. Microplastics alter feeding selectivity and faecal density in the copepod, Calanus helgolandicus. Science of the Total Environment 687, 780-789. Online.
Amazonian rainforest tree mortality driven by climate and functional traits
Izabela Aleixo, Darren Norris, Lia Hemeric, Antenor Barbosa, Eduardo Prata, Flávia Costa, & Lourens Poorter
The Problem: Climate scientists are constantly learning and sharing new details about climate change and its possible effects in the future. However, many of the impacts of climate change have already surfaced and revealed the fragility of our ecosystems. Recently, scientists have observed increasing tree mortality in tropical forests, which are some of the most biodiverse and ecologically important places in the world. Could tree mortality be another consequence of climate change–one that’s happening right now? This study by Aleixo and others (2019) explores this possible connection between modern climate change and downfall of tropical forests.
What data were used? This study uses monthly climate and tree mortality records along with about 50 years of observational data in the Amazon rainforest. Climate data include precipitation, temperature, and humidity. Tree mortality data is categorized by specific traits such as wood density (soft or hard), successional position (when a species colonizes a new area), and leaf phenology (deciduous or evergreen).
Methods: Aleixo and others (2019) tracked global climate and tree mortality in an area of the Amazon rainforest monthly for one year. They looked for increased tree mortality that aligned with variations in the climate data. They also examined tree mortality of different species traits during significant climate events in the past 50 years. These events include climate anomalies like El Niño or La Niña (click here to learn more about these).
Results: This study found that Amazon tree mortality is driven by climate, but the relationship is complex. For example, droughts can lead to immediate or slow tree death, depending on the mechanisms at play. Additionally, if a tree has harder wood, it is less likely to die during a drought. Aleixo and others (2019) also found that weather events like low rainfall or high temperatures can either immediately enhance tree mortality or cause increased mortality up to two years later. Similar outcomes are associated with years where El Niño or La Niña are particularly extreme. Various species traits may protect trees from dying under certain weather or climate events, but no single Amazon species is completely safe from the effects of climate change.
Why is this study important? As our climate continues to change and weather events become more extreme, the future of our forests remains uncertain. Even the most biodiverse and ecologically robust regions in the world are susceptible to the effects of climate change. This study provides a modern framework for us to understand those effects. From this, scientists can refine dynamic global vegetation models that predict how forests will respond to climate variability in the future.
Citation: Aleixo, I., D. Norris, L. Hemerik, A. Barbosa, E. Prata, F. Costa, and L. Poorter (2019), Amazonian rainforest tree mortality driven by climate and functional traits, Nature Climate Change, 9(5), 384-388, doi:10.1038/s41558-019-0458-0.
A Critical Appraisal of the Placement of Xiphosura (Chelicerata) with Account of Known Sources of Phylogenetic Error Jesús A. Ballesteros and Prashant P. Sharma Summarized by Maggie Limbeck
What data were used? Data were collected from whole genome sequence projects and RNA sequence libraries for all 53 organisms included in this study. Because there are four living species of horseshoe crabs and many living representatives of arachnids (spiders, scorpions, ticks) genetic data was able to be used as opposed to morphologic (shape and form) data. Organisms from Pancrustacea (crabs, lobsters, etc.) and Myriapoda (centipedes and millipedes) were used as outgroup organisms, organisms that are included in the analysis because they are part of the larger group that all of these animals fit into (Arthropoda) but have been determined to not be closely related to the organisms that they cared about in this study.
Methods: Several different methods were used in this study to estimate the evolutionary relationships between horseshoe crabs and arachnids. By using multiple different phylogenetic methods (different calculations and models to estimate relationships between organisms) these researchers had several different results to compare and determine what relationships always showed up in the analyses. In addition to all of these different methods that were used, two different scenarios were tested in each method. The researchers wanted to be able to run their data and see what results they got, but also test the existing hypothesis that horseshoe crabs are sister taxa to land-based arachnids.
Results: The vast majority of the phylogenetic trees that were produced in these different analyses showed that horseshoe crabs are “nested” or included in the group Arachnida and are sister taxa to Ricinulei (hooded tick spiders). The only analyses that returned results different from this, were those that were forced to keep horseshoe crabs as sister taxa to the land-based arachnids, but those trees had very low statistical support of being accurate.
Why is this study important? This study is particularly cool because it highlights interesting problems associated with using genetic data versus morphologic data and problems with understanding evolution in groups that diversified quickly. Chelicerates (the group of Arthropods that have pincers like spiders, scorpions, horseshoe crabs) diversified quickly, live in both aquatic and terrestrial settings, and have many features like venom, that all appeared in a short time frame geologically. By gaining a better understanding of the relationships between the members of Chelicerata and Arachnida researchers can start to look at the rates at which these features developed and the timing of becoming a largely land-based group. This is also an important study because it has demonstrated that relationships we thought were true for horseshoe crabs and arachnids for a long time may not actually be the case.
The big picture: The research done in this study really highlights the major differences in relationships that can be demonstrated depending on whether you are using morphological data or genetic data. This study found that by using genetic data for 53 different, but related organisms, that horseshoe crabs belong within the group Arachnida rather than a sister taxa to the group. It’s also really cool that this study was able to demonstrate evolutionary relationships that are contrary to what have long been believed to be true.
Jesús A Ballesteros, Prashant P Sharma; A Critical Appraisal of the Placement of Xiphosura (Chelicerata) with Account of Known Sources of Phylogenetic Error, Systematic Biology, syz011, https://doi.org/10.1093/sysbio/syz011
Morphospace expansion paces taxonomic diversification after end Cretaceous mass extinction
Christopher M. Lowery and Andrew J. Fraass
Summarized by Adriane Lam
The Problem: There is no doubt that species today are going extinct due to human activities, such as habitat loss, climate change, and the introduction of invasive species that take over areas. For example, the Florida Panther used to range throughout the southeastern U.S., but due to humans expanding into their habitat, they now only occupy a mere 5% of their former range. Polar bears are also facing loss of their habitat due to melting ice and snow caused by human-induced warming. But if humans were to disappear tomorrow, how long would it take for Earth’s flora and fauna to bounce back to the number of species before humans were here? This is a hard question to answer, but to begin to quantify this, paleontologists can use the fossil record.
In this study, the scientists looked at the time before, during, and after the end-Cretaceous mass extinction event that took place ~66 million years ago. This was one of the largest mass extinction events in Earth’s history, where about 75% of all species on Earth went extinct, including the non-avian dinosaurs. It is also an important mass extinction event to study because the event that wiped out all those species was very rapid. During other mass extinction events in Earth’s history, the extinction events themselves took on the order of millions to hundreds of thousands of years (read more about extinctions here).
The rate at which humans are altering the Earth today is unprecedented to any climate change event in the geologic past (see our ‘CO2: Past, Present, & Future’ page for more details). Thus, scientists need to compare the rate at which we are losing species today under a very fast climate change scenario to another event that was also very fast. Therefore, studying the end-Cretaceous mass extinction is particularly valuable: it was a very quick event and one that is most comparable to the rate at which we are losing species today.
Data Used: In this study, the scientists used the fossil record of planktic foraminifera to see how long it took for life to recovered after a mass extinction event, the end-Cretaceous mass extinction. Planktic foraminifera are single-celled protists (not animals) that live in open-marine environments. They have occupied our oceans for the past ~165 million years. These protists produce a calcium carbonate (same material seashells are made of) shell, or “test,” that grows to be about the size of a grain of sand. When the foraminifera die, its shell sinks to the seafloor. Over millions of years, these shells are preserved at the bottom of the ocean. Making the fossil record of planktic foraminifera an archive of extinction and evolution events for the past 165 million years of Earth’s history! The scientists who conducted this study used this amazing fossil archive to see how long it took these marine protists to return to pre-extinction levels after the end-Cretaceous mass extinction.
Methods: As part of his master’s project, Andy Fraass compiled a database of first and last occurrences of planktic foraminifera species. First and last occurrence datums are often used in paleontology to examine how long in geologic time a species existed. The authors used these data to examine when planktic foraminifera species evolved and went extinct (Figure 1).
This dataset collected, but left unpublished until this paper, also included measurements of the species’ tests, such as the number of chambers in the shell, how quickly the chambers expanded from the earliest chamber to the last, etc. From these measurements, the authors calculated test complexity. This is a metric that shows how ‘complex’ planktic foraminifera shells became through time. For example, a species with a simple shell might have simple chambers arranged in a spiral pattern. A more complex species might have a more extreme test (Figure 2). The test complexity of each species was then given a score, with 1 being the simplest, and 4 being the most complex or extreme.
In foraminifera, the shape of the test can be assumed to have some sort of relationship to the organism’s life strategy, or its niche, basically. A species’ niche is where and how it can live and interact with the environment. For example, humans occupy a broad range of niches: our technology allows us to live in very hot to very cold climates. On the other hand, polar bears have a very narrow niche. These animals only live in the tundra biome in the Northern Hemisphere on the ice and hunt seals. A specific foraminifera might only live at a particular depth in the ocean, or in water that’s above or below a certain temperature, or in regions with a certain abundance of food, etc. These niches are the scaffolding on which species diversity is built.
During a mass extinction event niche spaces are often completely disrupted or destroyed along with the species that occupy them. Thus, paleontologists have hypothesized that after an extinction event, the number of species cannot simply bounce back to what it was before, but the number and size of niche spaces has to be rebuilt first. This may cause the observed delay in the recovery of species after mass extinction events. This paper provided the first test of that hypothesis with real data.
Because the shape and characteristics of a planktic foraminifera’s shell is related to its niche, the authors used average test complexity of all the foraminifera that were alive at different points in time to reconstruct how many niches were occupied by forams before and after the end-Cretaceous mass extinction. Higher average complexity suggests a wider variety of niches were occupied, while lower complexity suggests that fewer niches existed.
Results: The authors found that there was a huge drop in the number of species after the end-Cretaceous mass extinction (Figure 1), which was not a surprise and something we have know about for a while. But the other finding was that along with a huge drop in the number of species was also a huge drop in the test complexity (Figure 3). It took about 5 million years for test complexity to reach the levels it was at before the mass extinction event. That’s a really long time!
Another interesting find is that test complexity increased before species diversified. That is, new niches were created faster than new species to fill them after the mass extinction event. This study shows that before a lot of new species can evolve, there need to be a few species that evolve and open new niche spaces first.
Why is this study important? Today, humans are having a huge effect on the ability of species to survive on our planet. Through destruction of species’ habitats and niche space, we are pushing more and more species to the brink of extinction. Importantly, there are also thousands of species that have already gone extinct from human activities (such as the Tasmanian Tiger, Passenger Pigeon, Sea Mink, Caribbean Monk Seal, Quagga, Elephant Bird, Haast’s Eagle, and many more). If we keep causing animals to go extinct, we may see a loss of biodiversity that rivals those of mass extinctions that have taken place in the geologic past. But until now, we didn’t really know how long it took for new niche spaces to be filled and how that would affect how fast new species can fill those niche spaces.
This study gives us a clue: it may take as long as 5 million years after a mass extinction event for new niche spaces to be created. It then takes additional five million years for diversity, or the number of species, to rebound to pre-extinction levels. The bottom line is that it takes 10 million years for the biosphere to recover from a mass extinction event. This means that even though humans have been on Earth for a very short period of time (geologically speaking), we will have a huge impact on the flora and fauna, even if we were to disappear tomorrow.
Citation: Lowery, C. M., and Fraass, A. J., 2019. Morphospace expansion paces taxonomic diversification after end Cretaceous mass extinction. Nature Ecology & Evolution https://doi.org/10.1038/s41559-019-0835-0
A seismically induced onshore surge deposit at the KPg boundary, North Dakota
Robert A. DePalma, Jan Smit, David A. Burnham, Klaudia Kuiper, Phillip L. Manning, Anton Oleinik, Peter Larson, Florentin J. Maurrasse, Johan Vellekoop, Mark A. Richards, Loren Gurche, and Walter Alvarez
Summarized by Jen Bauer, Maggie Limbeck, and Adriane Lam, who also comment on the controversy below
What data were used?
Data used in this study were identified from a new site, which the authors call Tanis (named after the ancient Egyptian city in the Nile River Delta), in the layers of rocks called the Hell Creek Formation. This formation is famous amongst paleontologists because it contains lots of dinosaur fossils from the late Cretaceous (about 66 million years ago). In this study, scientists found a new layer of fossils within the Hell Creek Formation that is unlike anything paleontologists have seen before. Those who found the site examined the rock’s features and fossils, which includes densely packed fish fossils and ejecta from the Chicxulub meteoric impact. The Chicxulub impact is what caused the dinosaurs to go extinct, and finding a layer of rock that was deposited minutes to hours after the impactor struck Earth is a very rare and exciting find.
This study included a variety of approaches. The rock features (called sedimentology) and fossil features of the Tanis area and event deposit are described to determine what caused this deposit in the first place. The authors also identified other pieces of evidence to aid in better understanding the situation at hand. Ejecta deposits were described as well, in comparison to ejecta deposits that are found closer to the impact site in the Yucatan Peninsula, Mexico.
Much of the sedimentology can be related to other aspects of the Hell Creek Formation in southwestern North Dakota that is an ancient river deposit that has some marine influence. In the Cretaceous period, central North America’s topography was very low which allowed for a seaway to form. This was called the Western Interior Seaway, and was home to a diverse number of animals such as plesiosaurs, mososaurs, large sharks, and ammonites. Several rivers likely drained into the Western Interior Seaway, much like the Mississippi River drains into the Gulf of Mexico today.
From studying the characteristics of the rocks within the Tanis site, the authors of the study concluded that this site was part of one of the rivers that drained into the Western Interior Seaway long ago. When the impactor struck Earth in the Yucatan Peninsula, it send huge waves (tsunamis) into the Western Interior Seaway and into the rivers that drained into the seaway. These huge waves pushed fish, ammonites, and other creatures into the seaway and into the rivers. The Tanis site is one such place where these animals that were pushed into the rivers were deposited and preserved. But not only were marine animals preserved at the site, but also land plants, such as tree limbs and flowers.
The fossils found in the Tanis deposits are all oriented in the same direction, indicating that they have been aligned by flowing water. The abundance and remarkable preservation of these fossil fishes and tree limbs suggest a very rapid burial event (the best preserved fossils are often the ones that experience very quick burial after death). The orientation of the fossils at the site along with the mix of marine and terrestrial life further supports that these fossils were deposited from very large waves from the asteroid impact disturbed this region.
Within the Tanis deposit there are also ejecta spherules, microkrystites, shocked minerals, and unaltered impact-melt glass. These are features that are commonly associated with the Chicxulub Impactor. When the impactor struck Earth, it was so hot it melted the underlying rock, sending tiny bits of molten rock into the atmosphere. These bits of molten rock quickly cooled and eventually fell back down to Earth, where today they are found all over the world. Today, these ejecta spherules and impact melt-glass all mark the huge end-Cretaceous mass extinction event that occurred 66 million years ago.
Why is this study important?
The Cretaceous-Paleogene (K/Pg) extinction event is one of the ‘Big Five’ mass extinction events (click here to read more about extinction). Like many extinction events, it is often difficult to determine the specific causes of mass destruction. However, the K/Pg extinction event is unique because scientists have many lines of evidence that a huge impactor struck Earth, sending clouds of ash and gas into Earth’s atmosphere. The new Tanis site that the authors uncovered preserves a snapshot into this catastrophic event.
This finding is very important because scientists know better understand what happened directly after the impactor hit Earth. In addition, several new species of fish have been discovered at the Tanis site, which will be important for additional studies about fish evolution through time.
DePalma, R.A., Smit, J., Burnham, D.A., Kuiper, K., Manning, P.L., Oleinik, A., Larson, P., Maurrasse, F.J., Vellekoop, J., Richards, M.A., Gurche, L., and Alvarez, W. 2019. A seismically induced onshore surge deposit at the KPg boundary, North Dakota. Proceedings of the National Academy of Sciences (PNAS), doi: 10.1073/pnas.1817407116
What’s all the commotion about?
It’s not every day that paleontologists make the national news, but this paper and the article written about it in the New Yorker (click here) caused a lot of commotion within the paleontological world. This is a great and potentially groundbreaking find, however, what caused the commotion was the sensationalist attitude of the New Yorker piece that left a lot of paleontologists uncomfortable. So what’s the big deal here? We break down a few (not all) of the issues with this article:
1. Breaking of Embargo
Although the published study is very exciting and will add greatly to our knowledge about the end-Cretaceous mass extinction event, the media hype around the study was handled very poorly for several reasons. All published studies go through peer review. This is when a paper is sent out to multiple other scientists who read the article and make sure that it is scientifically sound and is a good piece of science based upon other good science. During this waiting period while the paper is going through peer review or being finalized with publishers, the authors should avoid talking with popular media or publicizing their paper. When publishing in academia there is a period of time (embargo) where access to the findings of a paper is not allowed to the public. This is for a variety of reasons, having to do with copyright transfer, finances to support the journal or publisher, and more.
The New Yorker press article was released almost an entire week before being available for the community to examine. This means that the embargo was violated.
The reason embargos exist is to give journalists and the researchers they talk to some time to look at fresh findings and determine what the story is, whether it’s worth telling, and if there’s anything suspicious about what’s presented. – Riley Black (Slate article)
2. Paleontologists as Rough-and-Tough Dudes (and Unusual Folks)
The New Yorker article was also controversial because it framed paleontologists as belonging to a narrow demographic (read: white men who love the outdoors). Not all of us in paleontology are men, not all of us are white, and not all of us came into geology loving the outdoors (see the great diversity of folks working in paleontology on our ‘Meet the Scientist’ blog). Paleontologists have had to work very hard to break through the stereotypical conception of what we do and who we are, and this article did not help to address the great diversity of scientists working in the field of paleontology.
In addition, the New Yorker article only quoted and interviewed other male scientists, many of whom have been working in the field for decades. The article left out the voices of women and early-career researchers who have made valuable contributions to the field of paleontology. For more on this, read the Slate article by science writer, Riley Black “It’s Time for the Heroic Male Paleontologist Trope to Go Extinct”.
This article also reinforces the “lone-wolf” stereotype of geologists and paleontologists-a man going out west, few to no other people around, and spending his days looking for paleontological treasure. This image is perpetuated through the article because the author chose to continually highlight the privacy and secrecy asked by the De Palma. While this is certainly an attitude held by some paleontologists, the reality is that the majority of us work in teams. Time Scavengers is run by a large team of people and so is our research! Like working in any field, we all have our strengths and better science happens when we invite people to work with us who have different strengths and can help us.
Lastly, the article frames paleontologists in a not-so-flattering light. In one paragraph, the article states “…I thought that he was likely exaggerating, or that he might even be crazy. (Paleontology has more than its share of unusual people).” Firstly, what does unusual even mean? The STEM (Science, Technology, Engineering, Maths) fields are full of intelligent, diverse, and colorful folks from all walks of life. To imply that any one branch of science has ‘its share of unusual people’ is unfair and regressive.
3. Dinosaurs as the Star of the Show
Paleontology is not just diverse in terms of the people who work in the field, but also in terms of the different types of life that we work with. For example, our Time Scavengers team, we have folks who work with fossil plankton and echinoderms. In fact, most paleontologists work with invertebrates- animals that do not have backbones, or any bones at all. Some of the most foundational findings in paleontology are based on the fossil record of invertebrates and early vertebrates. Regardless, most of the public’s fascination lies with dinosaurs (we understand, they were gigantic, ferocious, and unlike anything that’s alive today).
However, this fascination with dinosaurs can lead to over exaggeration of studies and sensationalizing, which is exactly what happened with this article. The published study of the Tanis site only mentions one dinosaur bone out of all the fossils found. The real story here is about the wonderful assortment of fish, tree, and flower fossils, some of which are completely new to paleontologists.
Dr. Steve Bursatte, Paleontologist at University of Edinburgh commented on both the New Yorker article and the PNAS article on his Twitter account, click here to read more. He comments on the broken embargo and how the New Yorker article sensationalized the ‘dinosaur’ side of the story.
4. Proper Handling of Museum-Quality Specimens
The article that was published in the New Yorker raised a lot of concerns within the paleontology community regarding the handling and storage of the fossils that were found at the Tanis site. It is clear from the article that DePalma had a bad experience early on with fossils that he had loaned a museum not being returned to him, however, by maintaining control over the management of his specimens, it undermines those people working in museums who have degrees and years of experience handling fossil and other specimen collections. Anyone who has borrowed specimens from a museum knows the immense amount of paperwork that goes in on all ends to make sure the specimens leave a well documented trail.
Jess Miller-Camp, Paleontology Collections Manager and Digitization Project Coordinator at Indiana University commented on the New Yorker article and addressed her concerns as a museum professional, click here to read her Twitter thread. She comments on the process of loaning specimens to and from museums and proper ettiqute. Read her thread to learn more about this and why museums should be asked to comment.
In 1997, a T. rex nicknamed Sue was sold at a Sotheby’s auction, to the Field Museum of Natural History, in Chicago, for more than $8.3 million.
This quote is misleading. No museum would have adequate funds to secure Sue. The California State University system, Walt Disney Parks and Resorts, McDonald’s, Ronald McDonald House Charities, and other individual donors aided in purchasing Sue for the Field Museum. The Field Museum rallied resources to ensure this valuable specimen remained in a public institution.
In addition to proper storage and archiving of fossils, one of the key tenets of any kind of scientific research is reproducibility– how well can other scientists replicate the results that you got. In paleontology, being able to look at the exact same fossils that another scientists looked at is a key part to reproducibility, as well as allowing the science of paleontology to advance. Whenever a paleontologist finds something they think is “new” to science, or is a really important find (special preservation, currently undocumented here, etc.) if you want to publish a paper on that fossil, the fossil needs to be placed in a public institution like a museum or a similarly accredited fossil repository. This way, future scientists are able to track down that fossil you published on and continue working on understanding it, or using it in other studies. Keeping fossils that are published on in museums is also critical because it ensures that that fossil has a safe place to be stored after being worked on and is less likely to be lost in an office or lab space!
5. Respecting the Land and Indigenous People
In the field of paleontology, people, who are more often than not white, venture into another country or a part of the ‘wilderness’ to find fossils and sites that are completely new and never-before-discovered or seen. These lands that contain fossils were owned by indigenous people long before Europeans arrived in North America, and were likely known about centuries before. Often, when sensational popular science paleontology articles are published, the authors leave out the voices of indigenous people and respect for their land. In the New Yorker article, there was no mention of the indigenous people that lived in the Dakotas, or how their ancestors perceived the dinosaur and fish fossils in the area. To frame amazing paleontological finds as being in desolate wastelands is harmful and erases the narratives of people who have lived in these lands for centuries.
For a more thorough discussion on this topic, click here to read the Twitter thread by Dr. Katherine Crocker.
Click here to read a article written by Dr. Roy Plotnick in Medium that also summarizes the issues and causes of commotion surrounding this astounding find.
Global environmental consequences of twenty-first-century ice-sheet melt
Nicholas R. Golledge, Elizabeth D. Keller, Natalya Gomez, Kaitlin A. Naughten, Jorge Bernales, Luke D. Trusel, and Tamsin L. Edwards Summarized by Megan Thompson-Munson
The problem: Global policymakers rely heavily on scientific studies to inform their decisions about climate-related policies. However, many climate change scenarios outlined in these studies’ models fail to address the ice-ocean-atmosphere feedbacks that may be triggered by ice sheet melting.
What data were used? To incorporate ice-ocean-atmosphere feedbacks in their estimation of climate consequences, the authors use climate models and data from 23 empirical studies. These data include measurements of the changes in total ice mass, surface mass balance, ice shelf melt, and iceberg calving of the Antarctic and Greenland ice sheets.
Total ice mass is simply the volume of ice that makes up the ice sheet. Measuring the change in mass over time tells us whether the ice sheet is shrinking or growing, and at what rate that mass is changing. Spoiler alert: the ice sheets are most definitely shrinking.
A component of the changes to total ice mass is surface mass balance. This concept describes the balance between net accumulation and net ablation occurring on the surface of the ice sheet. The key process in accumulation is snowfall, while ablation is the process of melting. Thus, we can determine surface mass balance by subtracting the amount of melting from the amount of snowfall.
Two other components of determining changes to total ice mass are ice shelf melt and iceberg calving (Figure 1). Ice shelves are areas of the ice sheet that extend off the continent and over ocean water. When they melt, they directly feed the ocean with freshwater that had previously been trapped in frozen form. Similarly, the process of icebergs calving (i.e. when ice chunks separate from a marine-terminating glacier) removes mass from the ice sheet and adds it to the ocean.
Methods: The authors input a series of different climate scenarios into a model that predicts the effects of climate warming and ice sheet melting on ice-ocean-atmosphere feedback loops (Figure 2). Their model varies the monthly and yearly climate conditions over a period from 1860 to 2100 to assess the effects of thinning ice sheets. Starting the model in the past means that they can compare the predictions of the model with actual data from the 23 supplementary studies that collectively span 1900 to 2017.
Results: The model scenarios paired with empirical climate studies come to three main conclusions concerning the future thinning of ice sheets. First, as the Greenland Ice Sheet loses mass, the increasing amount of fresh meltwater will slow circulation of the Atlantic Ocean. The Atlantic meridional overturning ocean circulation (AMOC) is driven by temperature and salt gradients. Thus, a large contribution of cold freshwater would alter the speed of AMOC. Second, as Antarctica continues to deliver meltwater to the ocean, warm water will be trapped below the ocean surface. This creates a positive feedback loop in which Antarctic ice loss will increase from meltwater input to the ocean. Finally, the model predicts that any future ice sheet melt with elevate global temperature variability and contribute an additional 25 centimeters (10 inches) to sea level by the year 2100.
Why is this study important? Our climate is warming, the ice sheets are melting, and the consequences of those changes are substantial. We study past climates to better understand our modern and future climates, and we heavily rely on model predictions to look toward the future. This paper address a key component missing from many climate models (the ice-ocean-atmosphere feedbacks that may result from future ice sheet melting) and shows that some models have underestimated the severity of ice sheet melting consequences. Model predictions are critical tools in global policymaking, so ensuring that those models are comprehensive is essential. Moreover, this paper calls for continued observations of the effects of climate change on ice sheets, oceans, and the atmosphere. Further incorporation of data into models will only help improve their predictions of a future climate that demands new environmental policies.
Citation: Golledge, N.R., Keller, E.D., Gomez, N., Naughten, K.A., Bernales, J., Trusel, L.D., and Edwards, T.L., 2019, Global environmental consequences of twenty-first-century ice-sheet melt: Nature, p. 65-72, https://doi.org/10.1038/s41586-019-0889-9.
Antarctic ice sheet sensitivity to atmospheric CO2 variations in the early to mid-Miocene
Richard Levy, David Harwood, Fabio Florindo, Francesca Sangiorgi, Robert Tripati, Hilmar von Eynatten, Edward Gasson, Gerhard Kuhn, Aradhna Tripati, Robert DeConto, Christopher Fielding, Brad Field, Nicholas Golledge, Robert McKay, Timothy Naish, Matthew Olney, David Pollard, Stefan Schouten, Franco Talarico, Sophie Warny, Veronica Willmott, Gary Acton, Kurt Panter, Timothy Paulsen, Marco Taviani, and SMS Science Team
The Problem: The early to mid-Miocene (23 to 14 million years ago) is an interval of geologic time where atmospheric carbon dioxide (CO2) concentrations (about 280 to 500 parts per million) were similar to those that are projected for the coming decades under human-induced climate change. Thus, this interval of time is interesting for geologists because we can use the geologic record from this time to interpret how our oceans, atmosphere, and ice sheets ‘behave’ under warming scenarios. Understanding the extent to which the Earth will warm, weather patterns will change, and sea levels will rise in the coming decades can help scientists, the public, and policy makers prepare for our future. Related to sea level rises is understanding how much continental ice sheets, such as those on Greenland and Antarctica, will melt.
In this study, geologists use several methods to determine how sensitive Antarctic ice sheets are to increases in atmospheric CO2 concentrations 23 to 14 million years ago. The results from this study are useful in that we can determine how much Antarctic ice may melt in the coming decades, which would add to sea level rise.
Methods: To interpret how sensitive Antarctic ice is to atmospheric warming (or increased average global warming), the scientists use sediments obtained in a drilled core from the coastal margin of Antarctica (an ideal location to study the melting and growth of ice sheets). The core was drilled in 2006 and 2007 as part of the ANDRILL (ANtarctic DRILLing Project) scientific drilling project from the McMurdo sector of Antarctica. The core is approximately 1,138 meters long, and contain sediments that are dated at over 20 million years old!
This study is very unique and fun because the scientists use several proxies (or naturally-occurring records) to interpret what the margin of Antarctica looked like through time. The presence and abundance (or numbers) of plankton (such as foraminifera) and pollen grains indicate when the margin of Antarctica was warmer, and ice sheets had melted back. For example, when the ice around Antarctica melted back, this allowed more room and soil for plants to grow. The lithology, or general characteristics of the sediments and rocks collected in the ANDRILL core, was also used as a clue to the changing environment of Antarctica through the study interval. Just knowing the different sediment types through time is a very powerful proxy itself!
Results: Using all the different methods and proxies, the geologists were able to interpret how Antarctic ice sheets melted and re-grew through the Miocene interval. They determined that several times from 23 to 14 million years ago, ice grew and retreated inland. They found that Antarctic ice becomes very sensitive to small changes in the amount of carbon dioxide in the atmosphere.
To best illustrate their findings, the authors of this study created four ‘environmental motifs’. These are images of what the scientists think the Antarctic margin looked like through time. Note that there are only four motifs; these just capture the major environments that the scientists inferred from their data. There were likely other ‘in-between’ environments. But notice how dynamic the ice sheet around the Antarctic margin were: the ice melted and then re-grew quite a bit in response to warming and cooling events through the Miocene!
Why is this study important? This study highlights and solidifies the hypothesis that Antarctic ice sheets were very sensitive to changes in atmospheric carbon dioxide concentrations during the Miocene. The findings of the study also indicate that Antarctic ice will behave similarly under increased warming predicted for Earth’s future. Melting ice will have a huge impact on sea level, which will make living on coastal lands hard or impossible due to flooding.
Citation: Levy, R. H., Harwood, D., Florindo, F., Sangiorgio, F., Tripati, R., von Eynatten, H., Gasson, E., Kuhn, G., Tripati, A., DeConto, R., Fielding, C., Field, B., Golledge, N., McKay, R.,, Naish, T., Olney, M., Pollard, D., Schouten, S., Talarico, F., Warny, S., Willmott, V., Acton, G., Panter, K., Paulsen, T., Taviani, M., and the SMS Science Team, 2016. Antarctic ice sheet sensitivity to atmospheric CO2 variations in the early to mid-Miocene. PNAS 113(13), 3453-3458. doi: 10.1073/pnas.1516030113.