Climate-mediated changes in predator-prey interactions in the fossil record: a case study using shell-drilling gastropods from the Pleistocene Japan Sea
Tomoki Chiba and Shinichi Sato
Summarized by Baron Hoffmeister
What data were used? This study used a predator-prey analysis of drill holes found on fossil bivalve (clam) shells produced by gastropods (snails) found in the Oga Peninsula off the coast of Japan.
Methods: This study used computer analysis on fossil assemblages of bivalves to determine the location of predatory drill holes and the species of bivalves which indicated whether they are warm water dominant or cold water dominant species. The location of the drill holes on the bivalve shells was also analyzed to determine different predatory gastropods (Figure 1).
Results: This study showed that drilling predation was influenced by the change of sea surface temperatures and sea level due to glacial-interglacial climate cycles. A glacial period occurs due to cool temperatures and glacial advancement, and an interglacial period occurs when glaciers retreat and sea level rises due to warming temperatures. As warm water currents decrease, so does the presence of warm-water predator gastropods. This causes them to shift their range, therefore changing rates of predator and prey interactions. In this study, predation slowed as seawater temperatures decreased and in turn found that this moderated the predation pressure between the gastropods and bivalve prey. This study also found that predator and prey interactions in a shallow-marine ecosystem are likely to weaken with cooling temperatures and strengthen with warming temperatures.
Why is this study important? This study indicates that predator-prey relationships can be used to help interpret changing climates and the implications it has on ecosystems. This study also notes that ocean climate variability has large implications of range shifts which can be used to interpret how organisms respond to changing climate conditions.
The big picture: The information found in this study can be used to help interpret current-day climate change and its influence on predator-prey relationships in relation to the biogeographical distribution of species due to ocean temperatures. This is useful for identifying ecosystems globally.
Chiba, T., and Sato, S. I.. (2016). Climate-mediated changes in predator-prey interactions in the fossil record: a case study using shell-drilling gastropods from the Pleistocene Japan Sea. Paleobiology 42(2), 257–268. doi: 10.1017/pab.2015.38
A total 236 specimens were collected at a Lagerstätte deposit in Germany, which is a site with exceptional (in quantity or quality) fossil preservation.
Methods: The 236 specimens were classified by species, and then further classified by age range (i.e., juvenile, young adult, adult). Researchers began studying the fossils for signs of trauma that could have resulted from injury or skeletal diseases (pathologies). Due to the large availability of the Stenopterygius specimens, researchers dated and grouped them into three categories regarding the Toarcian Oceanic Anoxic Event (T-OAE). This was a time in the Jurassic Period when the oxygen levels were depleted and toxic greenhouse gases (e.g., carbon dioxide and hydrogen sulfide) became the major component of the atmosphere; the specimens were grouped as before T-OAE, during T-OAE, and after T-OAE. The purpose behind comparing pathological data to the T-OAE is to determine if the depletion of oxygen had any significant effect on marine health.
All of the data was inputted into a statistical software, R, to determine any significant correlations and variables.
Results: The data collected showed that trauma associated with healing was the most common pathology recorded; however, there was not a skeletal region significantly affected more than the others. These commonalities were shared by all five taxa of ichthyosaurs . Additionally, when comparing the overall size of the specimens and percentage of pathologies found, it was determined that the large species were approximately 2.4 times more likely to show signs of trauma and disease. This correlation was also found to be true when looking at the developmental data collected for Stenopteryguis; it was concluded that the adults were 4 times more likely to have signs of disease or trauma than the juvenile specimens.Regarding the data collected for the Toarcian Oceanic Anoxic Event , researchers could not find any significant data that could correlate an increase in pathologies due to the depletion of oxygen.
Why is this study important? This study showed the differences in skeletal pathologies present in a diverse set of marine reptiles. By differing in size, age, time, and ocean depth, researchers were able to obtain an overall survey of health and easily compare the pathology data to other ecological conditions (e.g., climate change).
The big picture:The research collected in this study provided a baseline for variables that affected the skeletal health of Jurassic marine reptiles. The data supporting the correlations between size and age range of different taxa within the extinct Ichthyosauria can be compared to other extant (i.e., living) reptiles to provide an estimation and a possible explanation for the prevalence of skeletal pathologies.
Citation: Palaeoepidemiology in extinct vertebrate populations: factors influencing skeletal health in Jurassic marine reptiles. (2019). Royal Society Open Science, 6(7). https://doi.org/10.1098/rsos.190264
What data were used? This study focused on the lives of 25 women from geographically different areas in Africa and Asia, including deserts, mountains, and deltas. Even though their cultures and livelihoods differed, they were connected by one phenomenon: climate change. Climate change is something that affects humanity as a whole, but the most severe impact will be felt by our vulnerable communities. As summers grow hotter and droughts increase, those whose livelihoods depend on natural resources will face extreme adversity in the coming years.
Methods: The focal point of the study was to investigate how a woman’s agency – or ability to make meaningful and strategic decisions – was impacted by her surroundings. During field research, each woman was interviewed and their livelihood, exposure to environmental risks (like cyclones, flooding, and storm surges), and societal standing were charted. Then, conditions like material possessions, supportive legal systems, and environmental stress were analyzed in each situation to measure the impact each had on the given woman’s life.
Results: With climate change leading to inconsistent rain and extreme temperatures, land becomes infertile and inadequate for farming. Men often migrate away in search of better job opportunities, and while this presents as a source of empowerment for women, with the chance of increasing their involvement in managing money, the research shows it was actually a burden. One young woman noted, ‘Men can easily migrate for work whereas we have to stay here (at home) to take care of the family’. The women were often left alone to provide food for their children and maintain the crops and pay the bills. Even in states with relief programs for floods and droughts, women were often excluded from receiving aid – reinforcing cultural norms that disadvantage women globally. The same trend can be seen in the United States right at this very moment, with up to 90% of women and minority business owners being excluded from the Paycheck Protection Program.
Environmental stress overshadowed the benefits women received from becoming a greater part in household decisions and in the workforce. Why? Because climate change has destructive consequences for the environment in which these women base their lives on. The struggle to simply survive in barren fields forces women to work harder, in poorer conditions, and for lower wages.
Why is this study important? This study provides vital information for governments to implement effective social programs for their citizens. It advances conversations about gender equality on the international stage and urges leaders to commit to gender equality when drafting important documents like the United Nations’ Sustainable Development Goals and the Sendai Framework for Disaster Risk Reduction.
The big picture: The negative environmental impacts of human-driven climate change are now inevitable: global temperatures will continue to rise, droughts will become more prevalent, and storms will intensify. It is important, now more than ever, to ensure that countries have the necessary social programs that can effectively help people sustainably adapt to the changing environment. Resources and adaptation strategies must be made available to the communities that are most vulnerable to fluctuating circumstances.
Citation: Rao, N., Mishra, A., Prakash, A. et al. A qualitative comparative analysis of women’s agency and adaptive capacity in climate change hotspots in Asia and Africa. Nat. Clim. Chang.9, 964–971 (2019). https://doi.org/10.1038/s41558-019-0638-y
Little Ice Age climatic erraticism as an analogue for future enhanced hydroclimatic variability across the American Southwest
by: Julie Loisel, Glen M. MacDonald, Marcus J. Thomson
Summarized by: Baron Hoffmeister
What data were used? This study used climate data from climate proxy databases and dendrochronology along with computer software for modeling climate patterns
Methods: This study used climate proxy data in conjunction with computer modeling and simulation software to determine hydroclimatic variability (i.e. the change in water conditions) in the North American Southwest.
Results: This study found that in the North American southwest is prone to variable climate conditions such as drought, as well as rapid snowmelt and severe rainstorms that can lead to flooding. Hydroclimatic variability in the southwest has not remained constant over the past one thousand years. In fact, there was high climate variability in the North American southwest during the Medieval Climate Anomaly (MCA; i.e. a period of warm climate that lasted from 950 c. to 1250) and the Little Ice Age (i.e. a period of cooling right after the MCA lasting until about 1850). Results show that the Little Ice Age had a higher amount of variability than the Medieval Climate Anomaly (see Figure 1). This was confirmed using climate data from tree ring growth analysis (i.e. the space between rings indicates the amount of growth) obtained by the North American Drought Atlas, a network of climate data points covering North America (figure 2), as well as climate proxy data from the El Junco diatom index from the Galapagos Islands. A diatom is a single-celled alga with cell walls made of silica. The oxygen used to make the silica is preserved in their shells and can be helpful climate proxy data.
This study also compared climate proxy records from fossil-coral oxygen isotopic records from Palmyra island in the tropical Pacific that recorded El Niño Southern oscillation patterns. El Niño Southern Oscillation is a weather pattern that has irregular periods of variation in wind and sea surface temperatures over the tropical eastern Pacific. Records of these weather patterns can be found in assemblages of certain coral fossils which serve as indicators for sea surface temperatures from the past. These were all analyzed and compared with the El Junco diatom index, and tree ring growth data using computer software. The researchers found a correlation between the El Niño Southern Oscillatory system and drought amplitude in the North American southwest increasing hydroclimatic variability. Also, with recent weather patterns, the computer simulations suggest that a ‘warm Little Ice Age’ scenario with high hydroclimatic variability accompanied by periods of warm and dry conditions is likely to occur sometime during the 21st century.
Why is this study important? This study shows how past climate change can help us understand how climate can change in the future and what the effects of that might be. In the North American southwest, hydroclimatic variability can lead to floods and drought impairing proper land management. Without experiments like this, climate change and its global effects cannot be understood. The results produced from this study can be used as a model for developing other climate reconstruction models.
The big picture: This study explores the potential for climate variability modeling using historical climatic data as a reliable indicator for future climate predictions. It is important to be able to understand these historical climate events and weather patterns along with their effects on environments. Successfully being able to do this can lead to well-rounded land and water resource management in the face of climate change.
Citation: Loisel, J., Macdonald, G. M., & Thomson, M. J. (2017). Little Ice Age climatic erraticism as an analogue for future enhanced hydroclimatic variability across the American Southwest. Plos One, 12(10). doi: 10.1371/journal.pone.0186282
The environmental consequences of climate-driven agricultural frontiers
L. Hannah, P. R. Roehrdanz, K. C. KB, E. D. Fraser, C. I. Donatti, L. Saenz, T. M. Wright, R. J. Hijmans, M. Mulligan, A. Berg, A. van Soesbergen
Summarized by Mckenna Dyjak
What data were used?:Climate-driven agricultural frontiers are areas of land that currently do not support the cultivation of crops but will transition into crop-yielding land due to climate change. The frontiers were identified using seventeen global climate-models (mathematical representations of atmosphere, land surface, ocean, and sea ice used to project future climates) for Representative Concentration Pathways 4.5 and 8.5 (RCPs, greenhouse gas concentration trajectory). The climates in which twelve globally important crops (corn, sugar, wheat soy, etc.) can grow were determined by using three modeling methods: Ecocrop (model of crop suitability based on known ranges of optimal temperature and precipitation), Maxent (used in determining species distribution under climate change) and the frequency of daily critical minimum and maximum temperatures provided by the NOAA Earth System Research Laboratory Twentieth Century Reanalysis Version 2. Water quality impacts, soil organic carbon impacts (consequences of the release of organic carbon preserved in soil), as well as biodiversity impacts (variety of life in an ecosystem) were data used in this study to determine the outcome of developing the frontiers.
Methods: The climate-driven agricultural frontiers were found by aligning the preferred climate of crops with the predicted climate determined by the RCPs. The water quality impact was analyzed by using a hydrological model to determine the fraction of water that would be contaminated by the agriculture on the frontiers. Soil organic carbon impacts were determined by using a global dataset that estimates the amount of soil organic carbon present at the top 100cm (soil can store some of the organic carbon that is cycled throughout the earth). The biodiversity impacts were assessed by compiling biodiversity hotspots, endemic (found only in a certain area) bird areas, and Key Biodiversity Areas and comparing them to the agricultural frontiers to find any overlap.
Results: The climate-driven agricultural frontiers were found to cover 10.3-24.1 million km2 of Earth’s surface; the areas can be seen in Figure 1. The models project that the largest portion of frontiers will be in the boreal regions of the Northern Hemisphere (e.g., places where coniferous trees- like pine trees- thrive) and mountainous areas across the world. In these areas, it was found that potato, corn, and wheat are the crops that will make the biggest contribution to the potential agriculture lands.
The release of carbon from the soils in the agricultural frontiers was predicted to be about 177 gigatons of carbon after 5 years of plowing took place on the untilled land (land not cultivated for crops). There is so much carbon stored in the topsoil layer of these frontiers that the 25-40% estimated release is equivalent to around 30 years of current US carbon emissions. These numbers do not include the release of carbon that will occur in the high-latitude soils due to warming alone. When analyzing the biodiversity impacts it was found that 56% of biodiversity hotspots, 22% of Endemic Bird Areas (EBAs), and 13% of Key Biodiversity Areas (KBAs) intersect with the agricultural frontiers. The fact that suitable climates for species will change with warming as well was taken into account (both crop and species suitability moves upslope). Water quality will be negatively affected by the biocide runoff in these frontiers and will affect 900 million to 1.6 billion people, as well as ecosystem health.
Why is this study important?: Russia is already discussing using the warming land to their advantage for developing agriculture and it is likely that Canada will as well. This study outlines the detrimental outcomes of cultivating these lands and urges for international policies for sustainable development of the frontiers. Due to climate change and unsustainable farming practices current farmland is becoming unusable. With a predicted increase in need for food due to a growing population, as well as unusable farmland, there will be a push for developing new lands; however, it is important to know the potential risks and how to mitigate them.
The bigger picture: With climate change and population growth occurring side by side it is important to know how to handle them in the worst-case scenarios and what measures will need to be taken to do so. It is also important to note that food insecurity is not usually linked to food production but rather to socio-economic disconnects such as food deserts (neighborhoods without healthy food sources).
Citation: Hannah L., Roehrdanz P. R., K. C. K. B. , Fraser, E. D. G., Donatti, C. I. , Saenz, L., Wright, T. M., Hijmans, R. J., Mulligan, M., Berg, A., and van Soesbergen, A. (2020) The environmental consequences of climate-driven agricultural frontiers. PLoS ONE 15(2): e0228305. https://doi.org/10.1371/journal.pone.0228305
Prolonged Fluvial Activity From Channel-Fan Systems on Mars
by: Gaia Stucky de Quay, Edwin S. Kite, and David P. Mayer
Summarized by: Lisette Melendez
What data were used? In geology, there’s a basic pillar called “The Principle of Uniformitarianism”. It suggests that geologic processes almost always occur in the same manner and intensity now as they did in the past – which is why geologists can look at the rock record to learn more about Earth’s future. In the same vein, many geologic processes that occur on Earth, like landslides, volcanoes, and erosions, can be used to study the same processes on different planets!
This study focused on analyzing pictures of alluvial fans (finger-like deposits that are usually created when running water in arid or semi-arid (e.g., deserts) flows downhill onto a flat surface, as shown in Figure 1) on Mars taken by the Context Camera (CTX) on the Mars Reconnaissance Orbiter (MRO). The scientists also compared Martian alluvial fans to the ones found here on Earth using elevation data collected by the NASA Shuttle Radar Topography Mission. These alluvial fans usually mark the end of a water channel, so they can be used to study ancient water deposits on Mars.
Methods: To study the channels of Mars, the CTX images were converted into digital elevation models, so information like width, slope, and height could be gathered from the data. The valleys on Mars were also measured for how closely they resembled a V-shape. Valleys shaped by rivers have a V-shape, while valleys shaped by other features, like glaciers, tend to have a U-shape.
After gathering all this data, the scientists desired to make an inference about the sediment on Mars, which is too small to be picked up by the camera. So, they turned to places on Earth that had alluvial fans that were very similar to the ones being studied on Mars: the Serra Geral in Brazil, the Great Escarpment in western South Africa, and the Western Ghats in India. These places were ideal parallels for the Martian surface because there’s little to no active tectonic plate movement in the area and the rocks are very well preserved over a long period of geologic time. The big difference is that instead of being placed along mountainsides or plateaus, the slopes that are being studied on Mars are usually along crater rims.
Results: The channels studied on Mars were found to be less concave (curved inwards) and have very steep slopes, indicating a dry environment. The data on concavity and erodibility (likeliness to erode away) on the Martian alluvial fans was most similar to the data found on the South African slopes, which reinforces the idea that the environment was similarly hot and dry.
Why is this study important? This study is another piece of evidence behind the idea that Mars was once full of water, before it underwent serious climate change. Understanding the history of water on Mars is crucial to understanding what conditions are necessary for life to evolve (which can help paleontologists learn about the first life on Earth, too!). It’s also interesting to note how we can learn more about planets that are millions of miles away by looking right here on Earth!
The big picture:More than a billion years ago, water used to run freely on the surface of Mars, creating channels and alluvial fans. Scientists use images of the geologic features that remained after water was no longer on the Martian surface to learn more about the history of the Red Planet and the potential implications for human exploration. Learning more about the surface and climate of Mars is necessary for understanding the hazards and potential resources that would be encountered on a crewed mission to Mars.
Citation: Stucky de Quay, G., Kite, E. S., & Mayer, D. P. ( 2019). Prolonged fluvial activity from channel‐fan systems on Mars. Journal of Geophysical Research: Planets, 124, 3119– 3139. https://doi.org/10.1029/2019JE006167
Triassic vegetation and climate evolution on the northern margin of Gondwana: a palynological study from Tulong, southern Xizang (Tibet), China
by: Jungang Peng, Jianguo Li, Sam M. Slater, Qianqi Zhanga, Huaicheng Zhu, Vivi Vajda
Summarized by: Kailey McCain
What data were used? Researchers noticed that while there was extensive research in North American and European paleobotany (i.e., plant fossils) from the Triassic period, data was very limited for Southern Asia. To fill this gap in knowledge, 147 samples were collected across China and examined for pollen, dust, and other microscopic fossils (also known as palynomorphs). Additionally, rock samples that dated through the Early Triassic were collected and processed.
Methods: The samples were processed using hydrochloric acid (HCl is strong acid and has a low pH value ~1) and hydrofluoric acid (HF is a weak acid and has a higher pH value ~6) lab techniques. By using these acids, the microfossils were isolated from the sediment sample and placed on a microscope slide for further investigation.
The palynology samples were tested for pollen and spores (cells that are capable of developing into a new individual without another reproductive cell). The abundance of specific species were then mapped to illustrate vegetation and climate during the Olenekian, a period of time during the Early Triassic. The identified microfossils can be seen in figure 1.
Results: The data collected showed that there are roughly three vegetation stages throughout the Early Triassic. The first stage is dominated by pteridosperms (fern-like vegetation lacking spores), which indicated a warm and dry climate. The following stage exhibited a decrease in pteridosperms and an increase in conifers (woody plants). This change in vegetation indicates a decrease in temperature and an increase in humidity. The final stage exhibits a steady increase in conifers and a diverse range in ferns, thus indicating a stable and temperate climate.
Using these stages, researchers were then able to compare the shifts in vegetation and climate to the tectonic activity due to the rifting (splitting) of Gondwana, an ancient supercontinent that split from Pangea. Through the examination of the rifts and ocean levels, the researchers hypothesized that the separation of Gondwana was a driving factor in regional climate and vegetation shifts.
Why is this study important? This study provided insights into the ways tectonic activity affected the environment in an area that lacked prior research. It drew important correlations between climate and tectonic activity. Additionally, evaluating the specific abundance and lack of certain vegetation helps establish evolutionary patterns not only in the Triassic, but also in supercontinents.
The big picture: Paleobotany and palynological data paint a great picture of what Earth was like during certain time periods. Specifically, the data collected in this study shows a correlation in Triassic vegetation and climate evolution during the rifting of Gondwana in Southern Asia.
Citation: Triassic vegetation and climate evolution on the northern margin of Gondwana: a palynological study from Tulong, southern Xizang (Tibet), China. (2019). Journal of Asian Earth Sciences, 175, 74–82. https://doi.org/10.1016/j.jseaes.2018.06.005
Experimental evidence for species-dependent responses in leaf shape to temperature: Implications for paleoclimate inference
by: Melissa L. McKee, Dana L. Royer, Helen M. Poulos
Summarized by: Mckenna Dyjak
What data were used?: Four species of seeds from woody plants were used: Boxelder Maple (Acer negundo L.), Sweetbirch (Betula lenta L.), American Hornbeam (Carpinus caroliniana Walter), and Red Oak (Quercus rubra L.). Three species from transfered saplings were also used: Red Maple (Acer negundo), American Hornbeam (Carpinus caroliniana Walter), andAmerican Hophornbeam (Ostrya virginiana K.Ko(Mill.)ch). The types of species were chosen because they each exist naturally along the east coast of the United States and have leaf shapes that vary with climate.
Methods:The seeds and saplings were randomly divided into either warm or cold treatments. The warm treatment cabinet had a target average temperature of 25°C (77°F) and the cold treatment cabinet had a target average temperature of 17.1°C (63°F). After three months, five fully expanded leaves were harvested and photographed immediately. The images from the leaves were altered in Photoshop (Adobe Systems) to separate the teeth (zig-zag edges of leaves) from the leaf blade (broad portion of the leaf). The leaf physiognomy (leaf size and shape) was measured using a software called ImageJ. The measured variables were tooth abundance, tooth size, and degree of leaf dissection. The degree of leaf dissection or leaf dissection index (LDI) is calculated by leaf perimeter (distance around leaf) divided by the square root of the leaf area (space inside leaf). The deeper and larger the space between the teeth of the leaf, the greater the LDI.
Results:The leaf responses to the two temperature treatments are mostly consistent with what is observed globally: the leaves from the cool temperature treatment favored having more teeth, larger teeth, and a higher LDI (higher perimeter ratio). However, it was found that the relation between leaf physiognomy (leaf size and shape) and temperature was specific to the type of species.
Why is this study important?: Paleoclimate (past climate) can be determined by using proxy data which is data that can be preserved things such as pollen, coral, ice cores, and leaves. Leaf physiognomy can be used in climate-models to reconstruct paleotemperature from fossilized leaves. This study supports the idea that leaf size changes correlate with temperature change. However, the responses varied by species and this should be taken into account for climate-models using leaf physiognomy to infer paleoclimate.
The bigger picture: Studying paleoclimate is important to see how past plants reacted to climate change so we have an idea how plants will respond to modern human-driven climate change.
Citation: McKee ML, Royer DL, Poulos HM (2019) Experimental evidence for species-dependent responses in leaf shape to temperature: Implications for paleoclimate inference. PLoS ONE 14(6): e0218884. https://doi.org/10.1371/journal.pone.0218884
A new model of Holocene reef initiation and growth in response to sea-level rise on the Southern Great Barrier Reef
by: Sanborn et al.
Summarized by: Baron Hoffmeister
What data were used?: This study analyzed sediment cores taken from the One Tree Reef of the Southern Great Barrier Reef in Queensland, Australia. Data was collected from the layers and sediment grains found within core samples taken from 12 different locations on the reef.
Methods: This study used biogenetic facies interpretation (i.e. physical, chemical, and biological aspects found within sediment and rock formations) from core samples to reconstruct reef growth and sea-level conditions.
Results: This study concluded that reef growth after a significant sea-level rise in the Pleistocene occurred in three stages. The first stage occurred over eight thousand years ago and was a rapid and shallow coral growth in presumably clear water. The average growth was around 6mm per year. The second stage of reef growth was between seven to eight thousand years ago, and this occurred with either turbid (i.e. cloudy water) or deeper water (i.e. over 5 meters in depth) conditions. The average growth was around 3mm per year. The third stage of growth was composed of shallow branching coral assemblages averaging 5mm of growth per year. This was referred to as a “catch up” in the reef growth sequence and continued until the reef reached the top of the sea level. It is hypothesized that more sediment-tolerant corals continued to slowly build up across the reef during this time. These are the types of corals that are now dominant on the Great Barrier Reef. This study also successfully identified six coral assemblages, and three algae assemblages correlating with specificpaleoenvironments, creating a new model (see figure 1) for interpretation of samples containing similar assemblages for future studies. Using geochronology (i.e. dating rock formations) a lag of 700-1000 years of reef growth was confirmed in this experiment. There was a significant gap of growth on the wind-sheltered portion of the reef, which is the opposite of what was hypothesized previously (that corals would grow faster in wind-sheltered areas). Figure 1 shows a new model for reef growth response from the results found in this study.
Why is this study important? This study is important for determining how corals and other reef-building organisms respond to environmental change and stress like sea-level change. Understanding past environmental conditions are crucial for understanding how current environmental conditions can affect reef growth today.
The big picture: This study not only provides new and important data of reef growth response to historical climatic changes but can also be used to predict present-day reef response to sea-level change.As sea level continues to occur, a more comprehensive understanding of the way coral and reef-building organisms respond to environmental changes could lead to preserving the reefs as the ocean conditions change. The new model this study found can provide important data for how reefs grow, and provide importantpaleoenvironmental interpretation data.
Citation: Sanborn, Kelsey L., Jody M. Webster, Gregory E. Webb, Juan Carlos Braga, Marc Humblet, Luke Nothdurft, Madhavi A. Patterson et al. “A new model of Holocene reef initiation and growth in response to sea-level rise on the Southern Great Barrier Reef.” Sedimentary Geology 397 (2020): 105556. https://doi.org/10.1016/j.sedgeo.2019.105556
Craters, Boulders, and Regolith of (101955) Bennu Indicative of an Old and Dynamic Surface
by: K. J. Walsh, E. R. Jawin, R.-L. Ballouz, O. S. Barnouin, E. B. Bierhaus, H. C. Connolly Jr., J. L. Molaro, T. J. McCoy, M. Delbo’, C. M. Hartzell, M. Pajola, S. R. Schwartz, D. Trang, E. Asphaug, K. J. Becker, C. B. Beddingfield, C. A. Bennett, W. F. Bottke, K. N. Burke, B. C. Clark, M. G. Daly, D. N. DellaGiustina, J. P. Dworkin, C. M. Elder, D. R. Golish, A. R. Hildebrand, R. Malhotra, J. Marshall, P. Michel, M. C. Nolan, M. E. Perry, B. Rizk, A. Ryan, S. A. Sandford, D. J. Scheeres, H. C. M. Susorney, F. Thuillet, D. S. Lauretta and the OSIRIS-REx Team
Summarized by: Lisette Melendez
What data were used? Unlike geologic sites on Earth, scientists aren’t able to use field work to determine the geologic history of celestial objects like asteroids, planets, and distant moons. Instead, planetary geologists rely on data collected by scientific instruments on spacecraft, like cameras and spectrometers, to study these unreachable geologic features.
The data for this study was gathered from images taken by NASA’s ORISIS-Rex spacecraft, whose mission is to travel to a near-Earth asteroid named Bennu. Asteroids are the remains of the building blocks of our solar system that enabled the rise of planets and life, and most of them reside in the Main Asteroid Belt. However, sometimes asteroids are ejected and enter the inner solar system (i.e. the rocky planets: Mercury, Venus, Earth, and Mars), becoming near-Earth asteroids. This asteroid, Bennu, was chosen for the sample collection mission because of its proximity to Earth, large size (almost 500 meters long!), and carbonaceous (i.e., carbon-rich) composition. The carbon-rich part is important because these asteroids contain chemical compounds and amino acids that would have been present at the beginning of our Solar System. Even though the asteroid is relatively long compared to other asteroids, it’s only about as wide as the length of the Empire State Building!
The spacecraft is set to bring back a sample of this asteroid to Earth by 2023 for scientists to analyze. In late 2018, the spacecraft began the approach phase of the mission and used its cameras to take high-quality pictures of Bennu’s surface, as shown in Figure 1. These images are not only used to determine a good sample collection site, but scientists also use them to learn more about the geologic processes on Bennu’s surface. By weaving the images together, the team was able to produce a three-dimensional model of the asteroid and determine the location of boulders on the surface of Bennu.
Methods: The surface of Bennu was mapped out by visually analyzing images taken by cameras on OSIRIS-Rex. Scientists combined image and radar data to measure the size and distribution of boulders on Bennu’s surface. By applying the same foundational geologic concepts observed here on Earth, scientists can draw conclusions about the geologic features on asteroids and what forces potentially formed them.
Results: The orbit of a near-Earth asteroid is tumultuous, due to the possibility of collision with other asteroids and the forces exerted by Earth’s gravity, making a usual lifespan of a near-Earth asteroid only last around tens of millions of years. Usually, this would mean a young, consistently refreshed surface for these near-Earth asteroids. However, a detailed study of Bennu’s surface shows evidence of rocks that are hundreds of millions of years old – long before Bennu ever left the Main Asteroid Belt.
Boulders are the most prominent geologic feature on Bennu’s surface. As shown in Figure 2, they can be found all around the asteroid. Scientists noted that the size of various boulders are simply too large for them to have been formed in Bennu’s current orbit, pointing towards the possibility they were created during larger asteroid collisions in the main asteroid belt. This indicates that studying the boulders further may aid in the understanding of Bennu’s parent body (i.e., where the rocks were originally created) and conditions in the main asteroid belt.
Another interesting result from the study is that even though the resolution of the images was not clear enough to depict fine-grained particles, the scientists measured thermal inertia (tendency to resist changes in temperature) and found that the results were consistent with the existence of fine-grained particles on Bennu’s surface. Come the end of 2020, the spacecraft will start up the TAGSAM (Touch-and-Go-Sample-Acquisition-Mechanism) instrument, blow nitrogen gas onto the surface to stir up dust, and collect the sample – leading to even more scientific discoveries on the asteroid front.
Why is this study important? This study is a reminder of how fascinating geology is: scientists were able to predict the history of the asteroid solely by measuring the size and distribution of boulders on its surface. This group was able to differentiate between events that occurred while Bennu was in the Main Asteroid Belt versus a near-Earth orbit, which helps us understand the environment right outside of Earth and beyond.
The big picture: By looking into the early Solar System, the data gathered in this study will help scientists understand the processes behind the formation of planets, as well as the origins of life. Additionally, the study will enhance our understanding of the evolution of near-Earth asteroids as well as the possibility of the asteroids impacting Earth.
Citation: Walsh, K.J., Jawin, E.R., Ballouz, R. et al. Craters, boulders and regolith of (101955) Bennu indicative of an old and dynamic surface. Nat. Geosci.12, 242–246 (2019). https://doi.org/10.1038/s41561-019-0326-6