This is the greatest mystery of our adult life: How can we spend all day typing at a computer and go home feeling exhausted? How could merely activating the small muscles of our fingers leave us worn out at the end of the day? What causes mental fatigue?

“It is kind of a mystery, to be honest.” said Michael Inzlicht, a University of Toronto psychologist who studies self-control, motivation, and fatigue. But scientists do have some clues. There is a hypothesis for why we get so tired from work when we're not physically active. We get so tired because our motivation runs out. As we work on a task, we struggle to focus on it or eventually lose interest in it. We become less motivated to do the task. We become drawn to the things we want to do (browsing social media or reading music blogs, for instance) rather than the things we have to do. And this tension possibly causes fatigue.

Researchers in the UK published new evidence that finds some indirect evidence for the motivational model. This study tracked 100 nurses in the UK over two 12-hour shifts.

Throughout the shifts, the nurses reported how fatigued they felt at regular intervals. They also wore devices that monitored and tracked the amount of physical activity they were engaged in. When the researchers investigated what could possibly explain the fatigue, they found some interesting patterns. Here's the result: There was no connection between the amount of physical work the nurses did and their feelings of fatigue. Instead, they found this small connection: The nurses who were least likely to feel fatigued from their work also felt the most in control of their work, and the most rewarded for it. These feelings may have boosted their motivation, which may have boosted their perception of having energy.

Inzlicht has also found evidence for the motivational model in his work. A few years ago, he and Carleton University psychologist Marina Milyavskaya monitored 159 students at McGill University in Canada for a week. “What was surprising to us was the biggest predictor of fatigue, not whether they had self-control.” Inzlicht said. “Instead, the predictor was the number of temptations they felt.” “If you're typing at work, and if you're anything like me, you got a few browsers open. These lead to temptations,” he said. “Temptations make us less motivated to do our work, which, in turn, may make us tired.”

And there may be an evolutionary reason for why our brains would do this. “As an organism, we need to meet multiple goals to survive.” Inzlicht explains. “We're not merely focused on finding food or pursuing our passions in life. We need to do all these things to be a healthy, thriving species.” Because these multiple goals compete with one another (for our time), we need a mechanism in place that signals. “Hey, stop doing that thing and do something else.” That mechanism, he suggests, could be fatigue.

In this light, boosting our motivation to stay on a task could lead us to feel less fatigued. One study found that just paying people some money when they’re exhausted can keep them on task. A similar thing is found in studies on physical endurance: People can be easily pushed to work beyond what they think is their physical limit.

John F. Kennedy said, “We’re tied to the ocean. And when we go back to the sea, whether it is to sail or to watch — we’re going back from whence we came.” This quote is more poignant than you might think. We are inevitably linked to the ocean: All life on Earth originates from its depths — and it is crucial for our future, too.

Covering about 71 percent of Earth’s surface, the ocean is instrumental in the processes that keep us alive. Whilst the rainforests may be referred to as “the lungs of the planet,” it is actually the ocean that provides 50 to 80 percent of the oxygen we breathe. Through a “conveyor belt” action, it helps regulate Earth’s climate by transporting heat away from the equator (赤道), towards the poles to cool. The ocean also proves itself essential in the fight against climate change. It absorbs 50 times more carbon dioxide (CO2) than our atmosphere — or rather, it is not the ocean itself…but what lives within it.

Many forms of aquatic life naturally absorb and hold carbon. From microscopic phytoplankton (浮游生物) to gigantic whales, life of all shapes and sizes play a part in feeding these carbon sinks (areas that absorb more CO2 than they release). Perhaps one of the most incredible forms is the humble seagrass.

Across the globe, there are more than 70 different species of seagrass. It grows in the vast underwater meadows of 159 countries on six continents, covering 300,000 square kilometers — barely occupying 0.2 percent of the seafloor. This is where the super seagrass comes into its own: It absorbs ten percent of the ocean’s carbon each year and captures carbon up to 35 times faster than tropical rainforests.

Seagrass constructs its leaves and roots through the use of carbon, which it gains from water through the process of photosynthesis (光合作用) — and it holds on to this carbon even after its death. Dead plant material slowly decomposes on the ocean floor, which means that the carbon stored within it ends up getting buried under the seabed.

It is ironic that such an effective natural solution to climate change is itself under threat from climate change, as temperatures rise and more violent storms destroy seagrass beds. Pollution, the long-term development of coastlines, and unregulated fishing have all played additional roles in its decline.

Experts say that reversing the decline of seagrass will take an international effort. Fortunately, restoration missions are already underway. The Ocean Conservation Trust, for example, has opened a seagrass cultivation lab. Here, seagrass is grown in batches, using seed-bearing shoots that have been hand-picked by divers. In April 2021, 2,200 bags of these seedlings were planted on the seabed of Plymouth Sound, England. They are expected to flourish into a meadow the size of six football pitches.

Could seagrass be one of the Earth’s great survivors that will end up saving us all? As with most things, only time will tell.

Even though they are lifeless objects, sand dunes (沙丘) can “communicate” with each other, researchers have found. A team from the University of Cambridge has found that as they move, sand dunes interact with their downstream neighbours and force them away.

It’s well-known that active sand dunes move around. Generally speaking, smaller dunes move faster and larger dunes move slower. And what hasn’t been understood is whether and how dunes within a field interact with each other.

“There are different views on dune interaction: one is that dunes of different sizes will hit each other until they form one giant dune.” said Karol Bacik, the study’s author. Now, Bacik and his workmates have shown results that query these explanations.

Water-filled flumes (水槽) are common tools for studying the movement of sand dunes in a lab setting, but the dunes can only be observed until they reach the end of the flume. Instead, Dr Nathalie Vriend, who led the research, and the members of her lab designed a circular flume, so that the dunes could be observed for hours, while high-speed cameras allowed them to record the movement of the dunes.

The two dunes in the study started with the same amount of sand. As the flow began to move across the two dunes, they started moving. At first, the front dune moved faster than the back dune, but as the experiment continued, the front dune began to slow down, until the two dunes were moving at almost the same speed. Besides, the type of flow across the two dunes was observed to be different: the front dune changed the flow’s direction, generated swirls (旋涡) on the back dune and pushed it away. As the experiment continued, the dunes got further and further apart.

“The next step for the research is to find evidence of large-scale and complex dune migration in deserts. By tracking clusters of dunes over long periods, we can observe whether measures to change the migration of dunes are effective or not, which will be a way to cope with the desertification (沙漠化),” Vriend said.