Ironwood

Since the dawn of time we relied on wood to create tools and build shelters. Yet, in just about every science fiction depiction of the future, wood is almost entirely absent. This is because wood has been eclipsed in recent decades by a range of alloys that are harder and more durable. While these tough alternatives are certainly useful, they are both expensive to produce and non-renewable. Indeed, there has long been interest in finding a sustainable and low-cost alternative to these materials. Now new work is revealing a way for wood to be hardened in a manner that will bring it back into use once more.

Metals are not the only materials to have replaced wood. Plastics, concrete and ceramics have also come to be used for the construction of products that were once made of wood. This is definitely not for the best. Many of these materials pollute the environment when produced and when junked at the end of their usable life. This has resulted in materials derived from wood seeing a resurgence since they are both cheap to make and quick to decompose when disposed of. The only catch is that wood materials cannot be used where strength and durability are essential.

Teng Li at the University of Maryland found this conundrum vexing since cellulose, the main structural component of wood, is reasonably strong to begin with and low in density. This struck him as encouraging since a low density meant that there was potential for a mix of chemistry and physics to make cellulose much harder by forcing its molecules into a smaller space and thus dramatically increasing its density. Keen to explore this, he worked with a team of colleagues to invent a procedure for creating wood that would be as hard as metal.

The researchers worked with samples of basswood, a timber that is both abundant and cheap. They suspected that they would need to remove a portion of the structural compounds lignin and hemicellulose to make it easier for the cellulose molecules to be compacted together. To do this, they soaked basswood samples in a solution of sodium hydroxide and sodium sulphite until they were completely saturated and sank to the bottom. Next, the solution was brought to a boil to accelerate the chemical removal of lignin in particular. Once this was done, the samples were rinsed with de-ionised water and then put under a hot press machine that exerted 20 megapascals on them for six hours to squeeze out excess lignin and drive out water that had migrated inside. The wood was then put in a 105 degree Celsius chamber to fully dry it before being immersed in oil for two days to make the surface water resistant.

When all of this work was complete, Dr Li and his colleagues ran a test on their creation known as the Brinell hardness test whereby a carbide ball was pressed into the modified wood at increasing pressures until it made a dent of 200 micrometers in size. This revealed that they had enhanced the hardness of basswood from a meagre value of 1.32 to a respectable 31.21. That value is not in the same league as steel, which has a Brinell hardness of 120 but it is twice that of aluminium, which has a value of 15, and close to the value of copper, which has a value of 35.

Pleased by this result, the team created table knives and nails with their hardened wood to try and determine how practical this material would be for being used in these sorts of items. When they examined the knives that they had made under the microscope they found that theirs were three times sharper than steel dinner knives that they had purchased at the store. This increased sharpness is because compacted cellulose molecules form a better edge than metal ones. As for the nails that they created the researchers found that they were easily smashed into timber with a hammer and did not break in the process. Given that such nails are lighter than steel and will never rust in the rain, the future may have a great deal more wood in it than many were expecting. This just published online in Matter. I wrote it up as a short piece for Economist Espresso.

Going with the flow

In a world trying to wean itself off of fossil fuels, power generation from other sources is becoming ever more important. Energy collected from ocean waves is getting increasing attention. The most common method employed in ocean energy harvesting is based on electromagnetic generators. These devices unquestionably work but they depend upon there being big waves to be effective. This has made them successful in places with choppy waters but lots of locations need energy and only have small waves for most of the time. These small waves carry energy too but are being ignored. Now new work is revealing a clever way to tap them.

Designed for catching some waves…

The device that the team behind this work have created is essentially a pendulum generator with a gear in the centre that is connected to the pendulum and a flywheel attached to a gear on either side of it. What makes this device special is that the gear in the centre is incomplete on one side. In other words, roughly one third of the gear lacks teeth (take a look at the image). This means it only makes contact with one flywheel gear when ocean waves are weak. However, when the waves get large, the pendulum swings far enough to drive the teeth of the incomplete gear to reach the second flywheel gear. At this point, both flywheels are being driven into action and creating resistance for the central incomplete gear.

The whole thing is rather cunning in that the contact with just a single flywheel keeps resistance low when waves are calm and thus is supportive of rather efficient power generation in mild conditions while large waves force contact with both flywheels, increasing resistance and power generation. All told, it is a generator that is adaptable in a way that current wave generators are not and it is this that gives it promise. You can read more in The Economist article that I wrote on this here.

Yet another reason to protect sea turtles and dugongs

We all know that land plants depend heavily on animals to distribute their seeds but what about plants in the ocean? While we don’t think about them much, ocean plants do flower and many of them produce fruits. But are there animals in the ocean that are eating the seeds of these fruits and dispersing them? Details on this have remained murky for years but now new work led by Samantha Tol at James Cook University in Australia published in Biotropica last month is revealing that large marine herbivores play a pivotal part in helping to distribute and germinate the seeds of seagrasses.

Seagrasses are incredibly important for providing fish that we depend upon places to live and for helping to control erosion by using their roots to bind sediment together that would otherwise just float away. And, like all plants, they have also long faced a problem. To pass along their genes to a new generation they must reproduce but, given that they don’t move once they have rooted down, a parent plant dropping seeds adjacent to itself immediately threatens its own offspring with competition for sunlight, water and soil nutrients. Some plants get around this problem by having seeds that drift off on the wind (like dandelions) or float away on water (like coconuts). Many others convince animals to do the job for them. While wind and water can send seeds a long way, animals are generally a better bet for long distance dispersal. This is the reason why so many plants have seeds that readily snag on fur or are encased in sugary fruits that entice animals to swallow them.

 Seeds that are swallowed on land almost always depend upon the digestive tract of the animal to chemical induce the seed to begin the germination process. Dr Tol knew that seagrasses, of which there are 72 species in the world, produce fruits containing seeds that are often ingested by large herbivores like sea turtles and dugongs. She also knew that these animals would sometimes end up over a hundred kilometres away before excreting them. This led her to wonder if travel through turtle and dugong digestive tracts was important for seagrass seed germination. Curious, she decided to run an experiment with a team of colleagues.

 The researchers went boating in Gladstone Harbour and Cleveland Bay in north-eastern Queensland where seagrasses, dugongs and sea turtles are common (along with man-eating salt water crocodiles). While carefully avoiding the crocodiles, they collected dugong and sea turtles faeces that had floated to the surface (their poo is buoyant). They then brought these samples back to the lab chilled where they were mined for tiny seagrass seeds. The team also collected seeds directly from the seagrass meadows at Gladstone Harbour.

 Both seeds collected from faeces and seeds collected from the seagrasses were placed into mesocosms that replicated the marine meadow environment. To also explore the role that temperature might have on seagrass germination and explore the possibility of global warming harming seagrasses in the future, some of these mesocosms were set at 19 degrees Celsius, some were set at 26 degrees and some were set at the very warm temperature of 32 degrees that climate models suggest the region may commonly experience in the future.

 After 60 days of monitoring the team saw that seagrass seeds benefitted greatly from travel through the guts of large herbivores. More specifically, 73% of the seeds collected from faeces that were placed in the cool mesocosm germinated, 87% germinated in the medium temperature tank and 83% germinated in the very warm tank. By comparison, these figures were only 29%, 20% and 36% respectively for the seeds that had not been consumed by turtles and dugongs. Germination time was also substantially sped up when it had gone through the digestive tracts.

 The findings reveal that dugongs and sea turtles are vital partners for seagrass ecosystems. That alone should encourage conservation efforts to be increased for these threatened species but there is a financial reason to look after them too. Seagrass communities provide a number of ecosystem services including food production from healthy fisheries, nutrient recycling and sediment control by enhancing seagrass spread that binds sediments together. Indeed, it is estimated that losing seagrasses equates to a cost of more than US $28,000 per hectare per year. For this reason alone it would be a very expensive mistake for us to allow dugongs and sea turtles to go extinct. All the more reason for them to be given better protection.

Far more than just a tourist attraction.

 Seeds that are swallowed on land almost always depend upon the digestive tract of the animal to chemical induce the seed to begin the germination process. Dr Tol knew that seagrasses, of which there are 72 species in the world, produce fruits containing seeds that are often ingested by large herbivores like sea turtles and dugongs. She also knew that these animals would sometimes end up over a hundred kilometres away before excreting them. This led her to wonder if travel through turtle and dugong digestive tracts was important for seagrass seed germination. Curious, she decided to run an experiment with a team of colleagues.

 The researchers went boating in Gladstone Harbour and Cleveland Bay in north-eastern Queensland where seagrasses, dugongs and sea turtles are common (along with man-eating salt water crocodiles). While carefully avoiding the crocodiles, they collected dugong and sea turtles faeces that had floated to the surface (their poo is buoyant). They then brought these samples back to the lab chilled where they were mined for tiny seagrass seeds. The team also collected seeds directly from the seagrass meadows at Gladstone Harbour.

 Both seeds collected from faeces and seeds collected from the seagrasses were placed into mesocosms that replicated the marine meadow environment. To also explore the role that temperature might have on seagrass germination and explore the possibility of global warming harming seagrasses in the future, some of these mesocosms were set at 19 degrees Celsius, some were set at 26 degrees and some were set at the very warm temperature of 32 degrees that climate models suggest the region may commonly experience in the future.

 After 60 days of monitoring the team saw that seagrass seeds benefitted greatly from travel through the guts of large herbivores. More specifically, 73% of the seeds collected from faeces that were placed in the cool mesocosm germinated, 87% germinated in the medium temperature tank and 83% germinated in the very warm tank. By comparison, these figures were only 29%, 20% and 36% respectively for the seeds that had not been consumed by turtles and dugongs. Germination time was also substantially sped up when it had gone through the digestive tracts.

 The findings reveal that dugongs and sea turtles are vital partners for seagrass ecosystems. That alone should encourage conservation efforts to be increased for these threatened species but there is a financial reason to look after them too. The ecosystem services that seagrass communities provide to fisheries fisheries and they role they play in sediment control equates to a cost of more than US $28,000 per hectare per year. For this reason alone it would be a very expensive mistake for us to allow dugongs and sea turtles to go extinct. All the more reason for them to be given better protection.

Tortoises with a taste for blood

We like to think of tortoises as herbivorous gentle giants. Indeed, most people (myself included) assume that their behaviours are simple because of their slow moving lives, . Now new work is revealing that at least some tortoises hunt and eat baby birds.

Tastes like chicken…

Those who study tortoises full time know that these reptiles are not strictly vegetarian. One species of semi-aquatic tortoise was spotted a number of years ago eating frogs in captivity. Several wild tortoise species have also been seen consuming bones and snail shells which many experts assume is done to increase their calcium intake. There have even been a few anecdotal reports of Galapagos giant tortoises squashing birds under the weight of their heavy shells but nobody has been sure whether this squashing accidental or deliberate.

The new work published in Current Biology is revealing (in video format no less) the deliberate hunting of a tern chick by a female tortoise in the Seychelles. In the video the tortoise walks directly towards the tern and reaches out with her mouth open when the chick is in reach. The chick , being no dummy, recognises an attack when it sees one and runs up a log to get away from the reptilian menace. The tortoise pursues while continuing to bite at the bird. The chick tries to defend itself by pecking at the tortoise and fluttering its wings but it is all to no avail. The relentless tortoise carries on attacking, driving the chick further and further along the log. At the end of the log the flightless chick is too high off the ground to jump off and gets pinned at a dead end. Sensing that she finally has her quarry cornered, the tortoise closes her jaws directly on its head killing it. The chick drops and the tortoise eats it.

This whole encounter was a long one (to be expected from an animal known for moving slowly). From first approach to the death of the chick, the interaction is seven minutes in length.

What is particularly notable here is that during the attack the tortoise approached the chick with its jaws wide open and the tongue retracted. Apparently, this is typical of aggressive tortoise behaviour and is in contrast to their normal feeding where the tongue is stuck out. The direct approach to the chick on the log also hints that the tortoise had experience at being able to capture a chick in such a situation by cornering it well above ground-level.

While this is the first documented incidence of a wild tortoise hunting, killing and eating a bird, the team have had their suspicions that this was going on as they had occasionally seen a few tortoises in the areas nibbling on bird carrion and observed what they thought looked like bird hunting behaviour. Now they are certain that at least this population of tortoises has turned omnivorous. Why this has happened and whether it is more widespread remain unclear. This just published in Current Biology and my article on it will be published in The Economist shortly.

Guided by poison-wielding rodents

We know that, long ago, our kin dispersed out of Africa through the Middle East many times but whether they crossed under a forest canopy or across a scorching desert has been a matter of fierce debate. The answer to this question matters because crossing through a forest would have been easy. Crossing a desert would have been hard and required technology, like pottery, to carry water. Now new work studying the fossils of the world's only poisonous rodent is revealing convincing evidence that forested corridors granted a pathway out of Africa.

Follow me, I know the way!

Image courtesy of Kevin Deacon.

The new work focuses upon the African crested rat, a bizarre species that rubs the sponge-like hairs on its back against poison collected from poison arrow trees to keep would be predators away. Found in the highlands of Kenya and Ethiopia today, these rats thrive in wet and densely vegetated woodlands where the poison arrow trees that they depend upon for protection grow well. Given that they are definitely not desert dwellers, the researchers were surprised when they realised that a whole bunch of rodent skulls that they had dug up in sediments of the southern Judean Desert were all an extinct subspecies of this very odd rat.

Fascinated by this discovery, the researchers used species distribution models to estimate the timing and location of habitats that would have been suitable for these poisonous rats to live in the region. The results suggest a brief period when forested corridors connected eastern Africa to the Middle East across the present-day Judean Desert, facilitating the dispersal of crested rats and, more importantly, our ancestors, out of Africa. This just published online in Proceedings of the National Academy of Sciences. My coverage of it in The Economist will publish shortly.