From a Pile of Rice to an Avalanche: A Brief Introduction to Granular Materials

Catalyst Volume 9

Communities living at the foot of the Alps need a way to predict the occurrence of avalanches for timely evacuation, but monitoring the entire Alpine range is impossible. Fortunately for those near the Alps, the study of granular materials has allowed scientists to move mountains into labs and use small, contained systems (like piles of rice) to simulate real-world avalanche conditions. Granular materials, by definition, are conglomerates of discrete visible particles that lose kinetic energy during internal collisions; they are neither too small to be invisible to the naked eye, nor too big to be studied as distinct objects.¹ The size of granular material situates them between common objects and individual molecules.

While studying extremely small particles, scientists stumbled upon an unsettling contradiction: the classical laws governing the macroscopic universe do not always apply at microscopic scales. For example, Niels Bohr sought to apply classical mechanics to explain the orbits of electrons around nuclei by comparing them to the rotation of planets around stars. However, it was later discovered that an electron behaves in a much more complicated way than Bohr had anticipated. At its size, the electron gained properties that could only be described through an entirely new set of laws known as quantum mechanics.

Though granular materials do not exist at the quantum level, their distinct size necessitates an analogous departure from classical thought. A new category of physical laws must be created to describe the basic interactions among particles of this unique size. Intuitively, this makes sense; anyone who has cooked rice or played with sand knows that the individual grains behave more like water than solid objects. Scientists are intrigued by these materials because of the variation in their behaviors in different states of aggregation. More importantly, since our world consists of granular materials such as coffee, beans, dirt, snowflakes, and coal, their study sheds new light on the prediction of avalanches and earthquakes.

The physical properties of granular flow vary with the concentration of grains. At different concentrations, the grains experience different magnitudes of stress and dissipate energy in different ways. Since it is hard to derive a unifying formula to describe granular flows of varying concentrations, physicists use three sets of equations to fit their states of aggregation, resembling the gaseous, liquid, and solid phases. When the material is dilute enough for each grain to randomly fluctuate and translate, it acts like a gas. When the concentration increases, particles collide more frequently and the material functions as a liquid. Since these particles do not collide elastically, a fraction of their kinetic energy dissipates into heat during each collision. The increased frequency of inelastic collisions between grains in the analogous liquid phase results in increasing energy, dissipation, and greater stress. Finally, when the concentration increases to 50% or more, the material resembles a solid. The grains experience significant contact, resulting in predominantly frictional stress and energy dissipation.¹

Avalanches come in two types, flow and powder, each of which requires a specific combination of the gas, liquid, and solid granular models. In a flow avalanche, the descending layer consists of densely packed ice grains. The solid phase of granular materials best models this, meaning that friction becomes the chief analytical aspect. In a powder avalanche, particles of snow do not stick together and descend in a huge, white cloud.² The fluid and solid models of granular materials are equally appropriate here.

Physicists can use these avalanche models to investigate the phenomena leading up to a real-world avalanche. They can simulate the disturbance of a static pile of snow by constantly adding grains to a pile, or by perturbing a layer of grains on the pile’s surface. In an experiment conducted by statistical physicists Dr. Daerr and Dr. Douady, layers of glass beads of 1.8 to 3mm in diameter were poured onto a velvet surface, launching two distinct types of avalanches under different regimes decided by the tilt angle of the plane and the thickness of the layer of glass beads.³

For those of us who are not experts in avalanches, there are a few key points to take away from Daerr and Douady. They found that a critical tilt angle exists for spontaneous avalanches. When the angle of the slope remained under the critical angle, the size of the flow did not grow, even if a perturbation caused an additional downfall of grains. Interestingly, when the angle of the slope was altered significantly, the snow uphill from the perturbation point also contributed to the avalanche. That means that avalanches can affect higher elevations than their starting points. Moreover, the study found that the angle of the remaining slope after the avalanche was always less than the original angle of the slope, indicating that after a huge avalanche, mountains would remain stable until a change in external condition occured.³ A. Often, a snow mountain with slopes exceeding the critical angle can remain static and harmless for days, because of the cohesion between particles.

Situations become complicated if the grains are not completely dry, which is what happens in real snow avalanches. In these scenarios, physicists must modify existing formulas and conduct validating experiments to predict the behaviors of these systems. Granular materials are not limited to predicting avalanches. In geophysics, scientists have investigated the relation of granular materials to earthquakes. For instance, one study used sound waves and glass beads to study the effects of earthquake aftershocks.⁴ Apart from traditional modeling with piles of rice or sand, the understanding of granular materials under different phases paves the way for computational modeling of large-scale natural disasters like avalanches and earthquakes. These studies will not only help us understand granular materials themselves, but also help us predict certain types of natural disasters.

References

1. Jaeger, H. M., Nagel, S. R., and Behringer, R. P. Granular Solids, Liquids and Gases. Rev. Mod. Phys., 1996, 68, No.4, 1259-1273.
2. Frankenfield, J. Types of Spring and Summer Avalanches. http://www.mountain-guiding.com/avalanche/info/spring-types.html (accessed Oct. 29, 2015).
3. Daerr, A. and Douady, S. Two Types of Avalanche Behaviour in Granular Media. Nature, 1999, 399, 241-243.
4. Johnson P. A., et al. Effects of acoustic waves on stick–slip in granular media and implications for earthquakes. Nature, 2008, 451, 57-60.

Not Many Other Fish in the Sea: Our Current Overfishing Crises

Catalyst Volume 9

Prevailing notions of the ocean make it seem as if it is "too big to fail” since it takes up 70% of the surface of Earth and contains 321,003,271 cubic miles of water.¹ Additionally, most of the oceans’ immense biodiversity has yet to be documented. The Census of Marine Life estimates that there could be between 178,000 to 10,000,000 different species living in ocean shoreline habitats due to the vast abundance of photosynthesizing microbes.² However, like any ecosystem, the oceans are not immune to anthropogenic and environmental stressors such as overfishing, climate change, and pollution. There are many interconnected problems surrounding the way in which people currently treat the oceans. Extracting large amounts of fish for human consumption threatens the dynamic balance that currently exists and threatens scientists’ potential for making groundbreaking discoveries about what lies below.

In 2010, the United Nations predicted that over 80% of the world’s fish are reported as fully exploited or overexploited, and thus “require effective and precautionary management.”³ Overexploitation refers to the extraction of marine populations to unsustainable levels.4 Fishing techniques have become exponentially more efficient since the Industrial Revolution, focusing on getting the largest catches in the fewest trips. Today’s fishing fleets are so large that it would require two to three times Earth’s supply of fish to fill them.⁴ These harmful practices lead to three main types of overfishing:

1. Growth overfishing: The removal of larger fish leaves behind only individuals that are too small to maximize the yield, or full amount of fish that could theoretically be obtained.⁵
2. Recruitment overfishing: When adult fish are excessively taken out of the ecosystem, recruitment and stock productivity decreases.⁵
3. Ecosystem overfishing: The targeting of a particular species leads to serious trophic cascades and ecological consequences.⁵

Unfortunately, the most popularly consumed fish species are subject to all three practices. Bluefin tuna, sturgeon, sea bass, and Atlantic salmon are examples of large, long-lived predatory species that only provide a few offspring each breeding cycle.⁵ For example, Bluefin tuna release ten million eggs each year, but only a small number survive to adulthood. Even then, these tuna do not reach reproductive maturity until eight to twelve years of age.⁶ When the largest fish are specifically targeted, many ecological consequences arise. Removing the largest fish of the largest species in an ecosystem significantly decreases the mean size for that species. As a result, only smaller fish are left to reproduce.⁷ This shift causes trophic level decline: as species at higher trophic levels are overfished, fishermen decide to catch the comparatively larger fish at lower trophic levels.⁷ This vicious cycle continues so that the average size of fish consumed decreases significantly. This phenomenon, known as “eating down the food chain,” puts many fish at risk, including herbivorous fish in coral reef ecosystems.⁷ To maintain a coral-dominated state, herbivorous fish consume macro-algae that otherwise would overgrow and suffocate corals. When coral-dominated reefs become overtaken by macro-algae, habitats for many other fish and organisms are severely reduced. Over 25% of the world’s fish species live exclusively within these three-dimensional coral communities, which themselves only take up 0.1% of the ocean floor.⁵ Not only are species being depleted at the very top of the food chain, smaller species that are endemic to specific ocean environments are also indirectly experiencing survival pressure.

These problems are further magnified by the fact that current fishing practices produce a large amount of by-catch, or the incidental capture of non-target species.⁵ The rustic image of a humble fisherman using a single hook at the end of a line no longer reflects reality for most commercial fishermen. Now, longlines are weighted at the bottom and can have as many as 3,000 hooks attached, probing deeper into the water column.⁸ A similar weighted system exists for large fishing nets, known as trawl nets, so that shellfish and other small or bottom-dwelling organisms can be collected in larger quantities. Bottom trawling, the practice of dragging a trawl net across the ocean floor, has contributed to 95% of the damage inflicted on deep water systems by destroying and smothering benthic communities.⁹ These practices are non-specific in nature, and thus collect anything and everything that attaches or gets caught. Fishing gear alone has threatened around 20% of shark species with extinction and leads to over 200,000 loggerhead sea turtles deaths annually.¹⁰ Sylvia Earle, a renowned ocean-conservationist, describes these unsustainable fishing practices as “using bulldozers to kill songbirds.”¹¹

The United Nations now predicts that by 2050, the world will run out of commercially viable catches and oceans could turn fishless.³ Driving this problem is the fact that seafood consumption has increased over the past 30 years.¹² Many coastal communities and developing countries rely on fishing as their main source of income and protein, with approximately 2.9 million people relying on fish for over 20% of their animal protein intake. One of the largest importers, the United States, imports 91% (by value) from other countries with lower production costs.¹³ The cheap labor comes from subsistence fishermen, who meet this increased demand by opting for unsustainable practices. Consequently, a “poverty cycle” emerges, where short-term survival takes precedence over sustainability and conservation efforts, further exacerbating ecological and economic damages.¹⁴

Recognizing that environmental considerations alone could put many developing countries at risk, policymakers have adopted a community-based approach in the planning, construction, implementation, and management of preservation policies.¹⁵ This ecosystem approach to fisheries, strives to ensure that the capability of aquatic ecosystems to provide the necessary resources for human life is maintained for present and future generations.¹⁶

The establishment of Marine Protected Areas, or MPAs, is another effective technique similar to the National Park Service’s preservation programs. Although MPAs have a wide range of management plans and enforcement, all strive to limit or restrict human activity so that natural populations can be restored.⁵ Allowing an environment to restore its fish populations without any human mitigation can take a long time, and the most effective MPAs extend across large tracts of area that can more fully encompass fish populations and migratory species.⁵ Because these areas often overlap with highly profitable fishing zones, MPAs are regularly met with backlash from coastal communities and later can be hard to enforce.¹⁷

These international efforts to reduce the amount of seafood extracted from ocean environments are generally invisible in a grocery store, so it is easy for consumers to engage passively with the food they see. However, recognizing the production, labor, and ecosystem that goes into fish and fish products (and all foods) is critical for maintaining the livelihood of the world’s natural environments. The ocean may seem vast, but there is not an infinite supply of resources that can meet current demands.

References

1. National Oceanic and Atmospheric Administration. http://oceanservice.noaa.gov/facts/oceanwater.html (accessed Oct. 31, 2015).
2. Smithsonian Institute. http://ocean.si.edu/census-marine-life (accessed Nov. 1, 2015).
3. Resumed Review Conference on the Agreement Relating to the Conservation and Management of Straddling Fish Stocks and Highly Migratory Fish Stocks; United Nations: New York, 2010.
4. Marine Biodiversity and Ecosystem Functioning. http://www.marbef.org/wiki/over_exploitation (accessed Oct. 31, 2015).
5. Sheppard, C.; David,S.; Pilling, G. The Biology of Coral Reefs,1; Oxford University Press: 2009.
6. World Wildlife Foundation http://wwf.panda.org/what_we_do/endangered_species/tuna/atlantic_bluefin_tuna/ (accessed Nov. 1, 2015).
7. Pauly, D., et al. Science. 1998, 279, 860-863.
8. Food and Agriculture Organization. http://www.fao.org/fishery/fishtech/1010/en (accessed Feb. 25, 2016).
9. The Impacts of Fishing on Vulnerable Marine Ecosystems; General Assembly of the United Nations: Oceans and the Law of the Sea Division, 2006.
10. Monterey Bay Aquarium. http://www.seafoodwatch.org/ocean-issues/wild-seafood/bycatch. (accessed Oct. 31, 2015).
11. Saeks, Diane Dorrans. US oceanographer Dr. Sylvia Earle. Financial Times, Aug. 9, 2013.
12. The State of World Fisheries and Aquaculture; Food and Agriculture Organization; United Nations: Rome 2014.
13. Gross, T. ‘The Great Fish Swap’: How America Is Downgrading Its Seafood Supply. National Public Radio, Jul. 1, 2014.
14. Cinner, J. et al. Current Biology. 2009. 19.3, 206-212.
15. Agardy, T. M. ; Information Needs for Marine Protected Areas: Scientific and Societal; 66.3; Bulletin of Marine Science, 2000; 875-878.
16. Food and Agriculture Organization. http://www.fao.org/fishery/topic/13261/en (accessed Nov. 1, 2015).
17. Agardy, T.M.; Advances in Marine Conservation: The Role of Marine Protected Areas; 9.7; Trends in Ecology and Evolution, 1994; 267-270.

Nomming on Nanotechnology: The Presence of Nanoparticles in Food and Food Packaging

Catalyst Volume 9

Nanotechnology is found in a variety of sectors—drug administration, water filtration, and solar technology, to name a few—but what you may not know is that nanotechnology could have been in your last meal.

Over the last ten years, the food industry has been utilizing nanotechnology in a multitude of ways.¹ Nanoparticles can increase opaqueness of food coloring, make white foods appear whiter, and even prevent ingredients from clumping together.¹ Packaging companies now utilize nano-sized clay pieces to make bottles that are less likely to break and better able to retain carbonation.² Though nanotechnology has proven to be useful to the food industry, some items that contain nanoparticles have not undergone any safety testing or labeling. As more consumers learn about nanotechnology’s presence in food, many are asking whether it is safe.

Since the use of nanotechnology is still relatively new to the food industry, many countries are still developing regulations and testing requirements. The FDA, for example, currently requires food companies that utilize nanotechnology to provide proof that their products won’t harm consumers, but does not require specific tests proving that the actual nanotechnology used in the products is safe.² This oversight is problematic because while previous studies have shown that direct contact with certain nanoparticles can be harmful for the lungs and brain, much is still unknown about the effects of most nanoparticles. Currently, it is also unclear if nanoparticles in packaging can be transferred to the food products themselves. With so many uncertainties, an activist group centered in Washington, D.C. called Friends of the Earth is advocating for a ban on all use of nanotechnology in the food industry.²

However, the situation may not require such drastic measures. The results of a study last year published in the Journal of Agricultural Economics show that the majority of consumers would not mind the presence of nanotechnology in food if it makes the food more nutritious or safe.³ For example, one of the applications of nanotechnology within the food sector focuses on nanosensors, which reveal the presence of trace contaminants or other unwanted microbes.⁵ Additionally, nanomaterials could be used to make more impermeable packaging that could protect food from UV radiation.⁵

Nanotechnology could also be applied to water purification, nutrient delivery, and fortification of vitamins and minerals.⁵ Water filters that utilize nanotechnology incorporate carbon nanotubes and alumina fibers into their structure, which allows microscopic pieces of sediment and contaminants to be removed from the water.⁶ Additionally, nanosensors made using titanium oxide nanowires, which can be functionalized to change color when they come into contact with certain contaminants, can help detect what kind of sediment is being removed.6 Encapsulating nutrients on the nanoscale-level, especially in lipid or polymer-based nanoparticles, increases their absorption and circulation within the body.⁷ Encapsulating vitamins and minerals within nanoparticles slows their release from food, causing absorption to occur at the most optimal part of digestion.⁴ Coatings containing nano-sized nutrients are also being applied to foods to increase their nutritional value.⁷ Therefore, there are many useful applications of nanoparticles that consumers have already shown to support.

While testing and research is an ongoing process, nanotechnology is already making food safer and healthier for consumers. The FDA is currently studying the efficacy of nanotechnology in food under the 2013 Nanotechnology Regulatory Science Research Plan. Though the study has not yet been completed, the FDA has stated that in the interim, it “supports innovation and the safe use of nanotechnology in FDA-regulated products under appropriate and balanced regulatory oversight.”^8,9 As nanotechnology becomes commonplace, consumers can also expect to see an increase in the application of nanotechnology in food and food packaging in the near future.

References

1. Ortiz, C. Wait, There's Nanotech in My Food? http://www.popularmechanics.com/science/health/a12790/wait-theres-nanotechnology-in-my-food-16510737/ (accessed November 9, 2015).
2. Biello, D. Do Nanoparticles in Food Pose a Health Risk? http://www.scientificamerican.com/article/do-nanoparticles-in-food-pose-health-risk/ (accessed October 1, 2015).
3. Yue, C., Zhao, S. and Kuzma, J. Journal of Agricultural Economics. 2014. 66: 308–328. doi: 10.1111/1477-9552.12090
4. Sozer, N., & Kokini, J. Trend Biotechnol. 2009. 27(2), 82-89.
5. Duncan, T. J. Colloid Interface Sci. 2011. 363(1), 1-24.
6. Inderscience Publishers. (2010, July 28). Nanotechnology for water purification. ScienceDaily. (accessed March 3, 2016)
7. Srinivas, P. R., Philbert, M., Vu, T. Q., Huang, Q., Kokini, J. L., Saos, E., … Ross, S. A. (2010). Nanotechnology Research: Applications in Nutritional Sciences. The Journal of Nutrition, 140(1), 119–124.
8. U.S. Food and Drug Administration. http://www.fda.gov/ScienceResearch/SpecialTopics/Nanotechnology/ucm273325.htm (accessed November 9, 2015).
9. U.S. Food and Drug Administration. (2015). http://www.fda.gov/ScienceResearch/SpecialTopics/Nanotechnology/ucm301114.htm (accessed November 9, 2015).

Megafires

Catalyst Volume 9

In 2015, American forests were ravaged by larger and more destructive fires than ever before. One of the most devastating wildfires occurred in Washington State and burned over 250,000 acres of forest at a rate of 3.8 acres per second.¹ These unprecedented grand burns of over 100,000 acres have been justifiably coined by researchers as “Megafires.”² Unfortunately, megafires are becoming an increasingly common feature of the American West.

Although forest fires are a natural and essential part of a forest’s life cycle, scientific records show a worrisome trend. Data from the National Climate Center in Asheville, North Carolina indicate that recent fires burn twice the forest acreage as wildfires 40 years ago.³ In contrast to replenishing wildfires that promote forest growth, megafires scorch the landscape, disabling forest regeneration and leaving wastelands in their wake.² In other words, they burn forests so completely that trees are unable to regrow.⁴ The increased incidence of megafires accordingly threatens to cause environmental change, particularly in the Western United States.⁵ Once-rich forests are now in danger of depletion and extinction as they give way to grasslands and shrubs. Even the hardy Ponderosa Pine, previously thought to be completely flameproof, is succumbing to megafires.⁵

What is the future of our forests, and what can we, as custodians of our natural lands, do to shape this future? Can we prevent megafires? Understanding the contributing causes of megafires is essential in devising a solution to prevent them. Current thinking by various ecologists identifies three primary causative factors, both behavioral and environmental: new firefighting strategies, the rise of invasive species, and climate change.¹

Government policies that promote aggressive control of forest fires are deceptive in their benefits. Fire-fighters have become incredibly efficient at locating and extinguishing wildfires before they become too destructive. However, certain tree species that have flame- and temperature-resistant properties, such as the Pine Barrens, Lodgepole Pine, and Eucalyptus, require periodic fires in order to reproduce.⁶ When facing wildfires these types of trees survive, whereas other plant species perish. Since flame-resistant tree species are often native flora to forest ecosystems, the selective survival of these trees maintains the forest’s composition over time and prevents shrubs and grasslands from overrunning the ecosystem. Flame-resistant trees accomplish their phoenix-like regeneration and self-sustainability by releasing their seedlings during a wildfire. In addition, forest fires destroy flora that would impede the growth of new seedlings through competition for space and light. This regenerative effect of forest fires has even resulted in the return of certain endangered tree species.⁴ One example, the Jack Pine, maintains its seedlings in cones that melt in the presence of fire. A policy to extinguish fires prematurely can inhibit seed release, threatening Jack Pine forests and others like it.⁶ To date, aggressive government policies toward forest fire-fighting have led to significant changes in forest composition accompanied by buildup of tinder and debris on the forest floor. This accumulated undergrowth now fuels megafires that burn with unparalleled intensity and speed. In contrast, forest management policies that revert to the practice of allowing small, controlled fires to clear away debris would maintain the forest’s long-term survival.

Invasive, flame-susceptible species provide the perfect fuel for megafires. During their westward expansion in the 1880s, settlers were not the only ones to achieve Manifest Destiny. Several species of grass also made the journey. The most common of these species was the Cheatgrass, a grass native to Europe, southwestern Asia, and northern Africa.⁷ Cheatgrass was inadvertently brought to the Americas on cargo ships in the 1800s and has been a significant environmental problem ever since. The short life cycle and prolific seed production of Cheatgrass causes it to dry out by mid-June, meaning that it serves as kindling for fires during the summer. Cheatgrass increases the size and severity of fires since it burns twice as much as the endogenous vegetation.⁷ Since the native vegetation is slowly being choked out by Cheatgrass, the landscape of the American West is transitioning into a lawn of this invasive species, poised to erupt into an inferno.

Global warming, one of the environmental causes of megafires, is perhaps an even more critical and challenging threat than invasive species. In 2015, forest fires ravaged more than 9 million acres of the Western mainland United States and Alaska.³ Studies of global warming demonstrate that every degree Celsius of atmospheric warming is accompanied by a four-fold increase in the area of forest destruction. Thus, the increase in global temperature is directly associated with the prevalence of megafires.⁸ Since the 1900s, the average temperature of the planet has increased by 0.6 degrees Celsius, primarily in the twenty-first century.⁹ Typically, severe fires burn less often at higher altitudes, due to cooler temperature and greater moisture levels, but as global temperatures increase, these areas become drier and more prone to forest fires. This warming of the climate contributes to massive burns that are fueled by centuries of forest debris and undergrowth.⁹ Climate change also contributes to a lack of precipitation, which further contributes to the expansion and intensity of forest fires. Wildfires themselves also contribute to climate change; as they continue to burn they emit greenhouse gases, which can contribute to accelerating global warming.⁹

Ultimately, due to poor policy practice, a destructive cycle is forming that serves as a catalyst to megafires. Finding long-term solutions that will prevent the occurrence of megafires will require policy adjustments at the regional, national, and international levels.⁶ Currently policies are changing, endorsing smaller burns to limit build up for megafire fuel. As more data is being introduced about global warming, efforts are being made to find more renewable forms of energy such as solar and wind.⁹ Ideally, this shift in resources will limit the increase in global temperatures and reduce the risk of megafires. Lastly research is being done to develop grasses that can out compete the problematic Cheatgrass.⁷ If we can meet these challenges, then megafires may finally be extinguished.

References

1.  Why we have such large wildfires this summer. http://www.seattletimes.com/seattle-news/northwest/why-we-have-such-damaging-wildfires-this-summer/ (accessed Oct. 9, 2015).
2.  National Geographic: How Megafires Are Remaking American Forests. http://news.nationalgeographic.com/2015/08/150809-wildfires-forest-fires-climate-change-science/ (accessed Oct. 11, 2015)
3. Climate Central: The Age of Western Wildfires. http://www.climatecentral.org/news/report-the-age-of-western-wildfires-14873 (accessed Oct. 9, 2015)
4. Deadly forest fire leads to resurrection of endangered tree. http://blogs.scientificamerican.com/extinction-countdown/deadly-forest-fire-leads-to-resurrection-of-endangered-tree/ (accessed Oct. 9, 2015)
5. Rasker, thesolutionsjournal 2015, 55-62.
6. NPR: Why Forest-Killing Megafires Are The New Normal. http://www.npr.org/2012/08/23/159373770/the-new-normal-for-wildfires-forest-killing-megablazes (accessed Oct. 11, 2015)
7. Keeley, International Journal of Wildland Fire, 2007, 16, 96–106
8. Stephens, Frontiers in Ecology and the Environment 2014, 12, 115-122.
9. Climate Central: Study Ties Warming Temps to Uptick in Huge Wildfires. http://www.climatecentral.org/news/warming-huge-wildfire-outbreaks-19521 (accessed Oct. 21, 2015)

Homo Naledi – A New Piece in the Evolutionary Puzzle

Catalyst Volume 9

Human beings share 96% of their genome with chimpanzees,¹ which is why modern science has accepted the concept that humans and apes share a recent common ancestor. However, our understanding of the transition from these ancient primates to the bipedal, tool-wielding species that conquered the globe is less clear than many realize. One crucial missing chapter in the evolutionary story is the origin of our very own genus, Homo. Scientists believe that somewhere between two and three million years ago, the hominid species Australopithecus afarensis evolved into the first recognizably human species, Homo erectus. However, the details of this genealogical shift have remained a mystery. In 2013, a discovery made in the Rising Star cave by two recreational cavers may have provided revolutionary insight into this intractable problem.

The Rising Star cave lies 30 miles outside the city of Johannesburg in northern South Africa. A popular destination for spelunkers for the past 50 years, this cave is well-known and has been extensively mapped.² Two years ago, Steven Tucker and Rick Hunter dropped into the Rising Star cave in an effort to discover new extensions to the cave, with the hope of finding something more.² They found a tight crevice that was previously unexplored, which led to a challenging forty-foot drop through a chute. At the bottom, Hunter and Tucker came across scattered bones and fossils in what would later be named the Dinaledi chamber.² Hunter and Tucker consulted with Dr. Lee Berger, a paleoanthropologist at the University of Witwatersrand. It was clear to Dr. Berger that these fossils were not of modern humans -- an ancient hominid species had been discovered.²

Within weeks of this discovery, Dr. Berger assembled a qualified team and set up camp at the mouth of the Rising Star cave. In the largest hominid artifact discovery in Africa, over one thousand bones from multiple bodies were extracted and analyzed.²

As the fossils were being transferred out of the cave, paleoanthropologists at the surface worked to piece together a skeleton. Some aspects of this species’ bone structure were distinctly human, like the long thumbs, long legs, and arched feet.² Other features, including curved fingers and a flared pelvis, were indicative of a more primitive animal.² A large skull fragment from above the left eye of one of the skeletons allowed scientists to definitively determine this hominid’s genus.

The Australopithecus skull is characterized by a large orbital ridge above the eye, with a deep concavity behind it, leading to a flatter face with pronounced brows.³ The skull fragment collected by the team, however, had a shorter ridge and less of an indentation above the frontal lobe.³ This finding led the team to conclude that they had discovered a new member of the Homo genus, which Dr. Berger named Homo naledi. ‘Naledi’ in the Sotho language means ‘star,’ a reference to the vivid stalactites emanating from the ceiling of the Dinaledi chamber.³

Dr. Berger’s discovery in the Rising Star cave was an incredible breakthrough, but finding fossils is only half the battle. The next step is to find a place for this species in the million-year narrative of human evolution we have created.

In accomplishing this feat, a logical place to start is considering how the fossils of Homo naledi ended up in their final resting place. There were no signs of predation, as no other animal fossils were found at this location. In addition, these fossils accumulated gradually, meaning that the bodies did not all die from a single event. Dr. Berger postulated that these bodies were placed there with purpose, but intentional body disposal is an advanced social behavior which, up to this point, has only been exhibited by more evolved Homo species. The brain size of the discovered hominids is estimated to be between 450 and 550 cubic centimeters, about one third the size of Homo sapiens brain and only marginally larger than that of a chimpanzee.³ The possibility of such a small-brained animal engaging in intentional body disposal challenges ideas about the cognitive abilities necessary for such advanced social behavior. Dr. William Jungers, chair of anatomical sciences at Stony Brook University, argues that advanced social intelligence was not likely at play in this instance. He claims that “intentional corpse disposal is a nice sound bite, but more spin than substance […] dumping conspecifics down a hole may be better than letting them decay around you.”⁴

The idea of intentional body disposal is not the only one of Dr. Berger’s conclusions that has attracted criticism. Some in the scientific community argue that Homo naledi is a distant cousin, not a direct ancestor, of modern humans. Others, like UC Berkeley’s Dr. Tim White, argue that "new species should not be created willy-nilly,” and believe that these discoveries may just be fossils of Homo erectus.⁵ Biologist Dr. David Menton takes the small brain size of these hominids as well as well as their “sloped face” and “robust mandible” as indication that Homo naledi does not even belong in the Homo genus.⁶

It is clear that while the Homo naledi fossils are extremely significant in the scientific community, their placement within the story of human evolution is contentious. Our inability to definitively date the fossils makes the task even more challenging. However, Homo naledi’s unique mosaic of human and ape-like features provides support for a new model of human evolution that has recently gained traction in the scientific community. While scientists would prefer to draw a family tree of human ancestors with modern humans at the top, our evolution is not so simple. Dr. Berger likens the reality of evolution to a braided stream.² Like a collection of tributaries all contributing to a river basin, humans may have been the product of a collection of human ancestors, each contributing to our existence differently. We may never fully understand where we came from, but discoveries like Homo naledi bring us a little bit closer to completing the evolutionary puzzle.

References

1. Spencer, G. New Genome Comparison Finds Chimps, Humans Very Similar at the DNA Level. National Human Genome Research Institute [Online], August 31, 2005. https://www.genome.gov/15515096 (accessed March 1st, 2016)
2. Shreeve, J. This Face Changes the Human Story. But How? National Geographic [Online], September 10, 2015. http://news.nationalgeographic.com/2015/09/150910-human-evolution-change/ (accessed January 17, 2016)
3. Berger, L. R. et al. ELife [Online] 2015, 4. http://elifesciences.org/content/4/e09560 (accessed January 16, 2016)
4. Bascomb, B. Archaeology's Disputed Genius. PBS NOVA NEXT [Online], September 10, 2015. http://www.pbs.org/wgbh/nova/next/evolution/lee-berger/ (accessed January 19, 2016)
5. Stoddard, E. Critics question fossil find, but South Africa basks in scientific glory. UK Reuters [Online], September 16, 2015. http://uk.reuters.com/article/us-safrica-fossil-idUKKCN0RG0Z120150916 (accessed January 19, 2016)
6. Dr. Mitchell, E. Is Homo naledi a New Species of Human Ancestor? Answers in Genesis [Online], September 12, 2015. https://answersingenesis.org/human-evolution/homo-naledi-new-species-human-ancestor/ (accessed January 17, 2016)

Nano-Materials with Giga Impact

Catalyst Volume 9

What material is so diverse that it has applications in everything from improving human lives to protecting the earth? Few materials are capable of both treating prolific diseases like diabetes and creating batteries that last orders of magnitude longer than industry standards. None are as thin, lightweight, and inexpensive as carbon nanotubes.

Carbon nanotubes are molecular cylinders made entirely of carbon atoms, which form a hollow tube just a few nanometers thick, as illustrated in Figure 1. For perspective, a nanometer is one ten-thousandth the width of a human hair.¹ The first multi-walled nanotubes (MWNTs) were discovered by L. V. Radushkevich and V. M. Lukyanovich of Russia in 1951.² Morinobu Endo first discovered single-walled nanotubes (SWNTs) in 1976, although the discovery is commonly attributed to Sumio Iijima at NEC of Japan in 1991.^3,4

Since their discovery, nanotubes have been the subject of extensive research by universities and national labs for the variety of applications in which they can be used. Carbon nanotubes have proven to be an amazing material, with properties that surpass those of existing alternatives such as platinum, stainless steel, and lithium-ion cathodes. Because of their unique structure, carbon nanotubes are revolutionizing the fields of energy, healthcare, and the environment.

Energy

One of the foremost applications of carbon nanotubes is in energy. Researchers at the Los Alamos National Laboratory have demonstrated that carbon nanotubes doped with nitrogen can be used to create a chemical catalyst. The process of doping involves substitution of one type of atom for another; in this case, carbon atoms were substituted with nitrogen. The synthesized catalyst can be used in lithium-air batteries which can hold a charge 10 times greater than that of a lithium-ion battery. A key parameter in the battery’s operation is the Oxygen Reduction Reaction (ORR) activity, which is a measure of a chemical species’ ability to gain electrons. The ORR activity of the nitrogen-doped material complex is not only the highest of any non-precious metal catalyst in alkaline media, but also higher than that of precious metals such as platinum.⁵

In another major development, Dr. James Tour of Rice University has created a graphene-carbon nanotube complex upon which a “forest” of vertical nanotubes can be grown. This base of graphene is a single, flat sheet of carbon atoms ‒ essentially a carbon nanotube “unrolled.” The ratio of height-to-base in this complex is equivalent to that of a house on a standard-sized plot of land extending into space.⁶ The graphene and nanotubes are joined at their interface by heptagonal carbon rings, allowing the structure to have an enormous surface area of 2000 m² per gram and serve as a high potential storage mechanism in fast supercapacitors.⁷

Healthcare

Carbon nanotubes also show immense promise in the field of healthcare. Take Michael Strano of MIT, who has developed a sensor composed of nanotubes embedded in an injectable gel that can detect several molecules. Notably, it can detect nitrous oxide, an indicator of inflammation, and blood glucose levels, which diabetics must continuously monitor. The sensors take advantage of carbon nanotubes’ natural fluorescent properties; when these tubes are complexed with a molecule that then binds to a specific target, their fluorescence will increase or decrease.⁸

Perhaps the most important potential application for carbon nanotubes in healthcare lies in their cancer-fighting applications. In the human cell, there is a family of genes called HER2 that is responsible for the regulation of growth and proliferation of cells. Normal cells have two copies of this family, but 20-25% of breast cancer cells have three or more copies, resulting in quickly-growing tumor cells. Approximately 40,000 U.S. women are diagnosed every year with this type of breast cancer. Fortunately, Huixin He of Rutgers University and Yan Xiao of the National Institute of Standards and Technology have found that they can attach an anti-HER2 antibody to carbon nanotubes to kill these cells, as shown in Figure 2. Once inserted into the body, a near-infrared light at a wavelength of 785 nm can be reflected off the antibody-nanotube complex, indicating where tumor cells are present. The wavelength then increases to 808 nm, at which point the nanotubes absorb the light and vibrate to release enough heat to kill any attached HER2 tumor cells. This process has shown a near 100% success rate and leaves normal cells unharmed.⁹

Environment

Carbon nanotube technology also has environmental applications. Hui Ying Yang from Singapore has developed a water-purification membrane made of plasma-treated carbon nanotubes which can be integrated into portable, rechargeable, and inexpensive purification devices the size of a teapot. These new purifications devices are ideal for developing countries and remote locations, where large industrial purification plants would be too energy- and labor-intensive. Unlike other portable devices, this rechargeable device utilizes a membrane system that does not require a continuous power source, does not rely on thermal processes or reverse osmosis, and can filter for organic contaminants found in brine water - the most common water supply in these developing and rural areas.¹⁰

Oil spills may no longer be such devastating natural disasters either. Bobby Sumpter of the Oak Ridge National Laboratory demonstrated that doping carbon nanotubes with boron atoms alters the curvature of the tubes. Forty-five degree angles form, leading to a sponge-like structure of nanotubes. As these tubes are made of carbon, they attract hydrocarbons and repel water due to their hydrophobic properties, allowing the tubes to absorb up to 100 times their weight in oil. Additionally, these tubes can be reused, as burning or squeezing them was shown to cause no damage. Sumpter and his team used an iron catalyst in the growth process of the carbon nanotubes, enabling a magnet to easily control or remove the tubes from an oil cleanup scenario.¹¹

Carbon nanotubes provide an incredible opportunity to impact areas of great importance to human life - energy, healthcare, and environmental protection. The results of carbon nanotube research in these areas demonstrate the remarkable properties of this versatile and effective material. Further studies may soon lead to their everyday appearance in our lives, whether in purifying water, fighting cancer, or even making the earth a better, cleaner place for everyone. Big impacts can certainly come in small packages.

References

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3. Ecklund, P.; et al. Ugliengo, P. In International Assessment of Carbon Nanotube Manufacturing and Applications, Proceedings of the World Technology Evaluation Center, Inc. Baltimore, MD, June, 2007.
4. Nanogloss. The History of Carbon Nanotubes – Who Invented the Nanotube? http://nanogloss.com/nanotubes/the-history-of-carbon-nanotubes-who-invented-the-nanotube/#axzz3mtharE9D (accessed Sep 14, 2015).
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8. Understanding Nano. New implantable sensor paves way to long-term monitoring. http://www.understandingnano.com/carbon-nanotubes-implant-sensor.html (accessed Sep 20, 2015).
9. Understanding Nano. Combining Nanotubes and Antibodies for Breast Cancer 'Search and Destroy' Missions. http://www.understandingnano.com/nanomedicine-nanotubes-breast-cancer.html (accessed Sep 22, 2015).
10. Understanding Nano. Plasma-treated nano filters help purify world water supply. http://www.understandingnano.com/nanotube-membranes-water-purification.html (accessed Sep 24, 2015).
11. Sumpter, B. et al. Covalently bonded three-dimensional carbon nanotube solids via boron induced nanojunctions. Nature [Online] 2012, doi: 10.1038/srep00363. http://www.nature.com/articles/srep00363 (accessed Mar 06, 2016).
12.  Huixin, H. et al. Anti-HER2 IgY antibody-functionalized single-walled carbon nanotubes for detection and selective destruction of breast cancer cells. BMC Cancer 2009, 9, 351.