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The structure of Earth's crust seen in a 3D rendering with elements furnished by NASA. Photo credit: Rost-9D / iStock / Getty Images Plus

The Earth of 4.5 billion years ago was covered in hot magma that had to gradually cool for the planet to become habitable. This happened over millions of years, as the surface formed the hard rocks of the crust that is our home. The interior of our planet still emanates geothermal energy that causes plate tectonics to move, resulting in earthquakes and volcanoes. But how fast did Earth cool and how long will it continue to cool before the effects of its hot interior stop?

Professor Motohiko Murakami of ETH Zürich and colleagues from the Carnegie Institution of Science have developed a system to measure how well a mineral — bridgmanite — conducts heat. Bridgmanite makes up the boundary layer between the iron-nickel core of Earth and its mantle layer, and its thermal conductivity influences how fast heat flows through the core into the mantle. 

From their experiments, Murakami and the other scientists suspect that Earth may be cooling faster than previously thought. Their study, “Radiative thermal conductivity of single-crystal bridgmanite at the core-mantle boundary with implications for thermal evolution of the Earth,” was recently published in the journal Earth and Planetary Science Letters.

“This measurement system let us show that the thermal conductivity of bridgmanite is about 1.5 times higher than assumed,” Murakami said, as ETH Zürich reported. This finding suggests that core to mantle heat is also higher than was once believed, which accelerates the cooling of Earth.

Earth’s interior will eventually cool and solidify, and its plate tectonics will cease as well, possibly turning Earth into a sterile rock similar to Mercury or Mars, ScienceAlert reported.

Another factor in the rate at which Earth loses its heat is that when bridgmanite cools down it transforms into post-perovskite, a mineral that is more efficient at conducting heat and therefore increases the rate of heat loss from Earth’s core to its mantle.

“Our results could give us a new perspective on the evolution of Earth's dynamics,” Murakami said, as reported by ScienceAlert. “They suggest that Earth, like the other rocky planets Mercury and Mars, is cooling and becoming inactive much faster than expected.”

Additional research is needed to determine how long it will be before the convection currents in Earth’s mantle stop, reported. “We still don’t know enough about these kinds of events to pin down their timing,” Murakami said.

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Humans have been evolutionarily programmed to crave sugar. Photo credit: JLPH / Image Source / Getty Images

It’s the ingredient in food you try to avoid because you feel it’s too unhealthy, but it’s so delicious it’s hard to eat in moderation. Many of us love it, but at the same time rue its existence. It turns out this tricky additive many of us have a love/hate relationship with is also one that we as humans have been evolutionarily programmed to crave: sugar.

As we know, cakes, cookies and other sweetened foods are at the top of the food pyramid for a reason; we’re supposed to eat less of them. So why do we crave them so much? Stephen Wooding, an anthropologist and assistant professor at University of California, Merced, who studies the evolution of taste perception, may have the answer.

“The refined sugars we use today are no different from the ones found in nature — the problem is that they are much more abundant now than at any point in our evolutionary history. Humans lived for hundreds of thousands of years in environments where sugar was enticing but scarce. Now we can get as much as we want, and we want lots of it,” Wooding told EcoWatch.

As Wooding pointed out to The Conversation, getting enough food to eat was one of the most basic struggles of our ancient ancestors. The daily activities of getting enough food and shelter for themselves and their families used up a lot of calories, and those who were better at these things lived longer and had more children. In other words, “they had greater fitness, in evolutionary terms,” Wooding wrote in The Conversation.

And being able to detect the presence of sugars in prospective foods, particularly in plants, while foraging could give an individual a great advantage because, as we know, sugars are a wellspring of calories. When foods are sweet, it tells the person tasting them that sugars are present, and if the taster could also tell the amount of sugar the food might have, that would enable them to quickly decide whether or not they should invest the time and energy in “gathering, processing and eating the items,” Wooding wrote for The Conversation. “Detecting sweetness helped early humans gather plenty of calories with less effort. Rather than browsing randomly, they could target their efforts, improving their evolutionary success,” Wooding wrote.

According to Wooding, taste buds have subtypes of cells that respond to different aspects of taste, like salty, bitter, savory, sour or sweet. When you eat a food, the taste bud subtypes sense the food’s chemical makeup by making receptor proteins that correspond to these different “taste qualities.” The subtype that produces the bitter protein makes it when something toxic is present, while the savory protein is responding to amino acids, the molecules that combine to make proteins. As Wooding wrote in The Conversation, “Your ability to perceive sweetness isn’t incidental; it is etched in your body’s genetic blueprints.”

The receptor protein that detects sugars is called TAS1R2/3. Found in many different animals, the genes that encode the receptor protein are called TAS1R2 and TAS1R3 and have been around for hundreds of millions of years.

“Geneticists have long known that genes with important functions are kept intact by natural selection, while genes without a vital job tend to decay and sometimes disappear completely as species evolve. Scientists think about this as the use-it-or-lose-it theory of evolutionary genetics. The presence of the TAS1R1 and TAS2R2 genes across so many species testifies to the advantages sweet taste has provided for eons,” Wooding wrote for The Conversation.

Animals that don’t usually eat foods that contain sugars lose their ability to recognize it and thus have only remnants of the TAS1R2 gene, Wooding wrote. And just as the bitter receptors in the brain tell a person something is toxic and shouldn’t be eaten, since humans have evolved to need sugar for the calories and energy it provides, when the brain detects it, it tells you to keep eating. Since these responses have been favorable for generations, they become instincts due to natural selection. “Experiment after experiment finds the same thing: People are attracted to sugar from the moment they're born. These responses can be shaped by later learning, but they remain at the core of human behavior,” Wooding wrote for The Conversation.

When we’ve eaten a lot of sugar and start to feel sick, that’s our bodies’ way of telling us to stop, but it doesn’t always work in time to protect us from the longer-term effects of eating too much sugar.

“Our bodies send warning signals when we're eating too much of something, including sugars. A major problem is that for most people the signal comes too late, after we've eaten so much we're already storing fat and gaining weight,” Wooding told EcoWatch. “However, this isn't true for everybody. We all have a friend who seems to effortlessly stay at a healthy weight, but we also have friends who struggle to control it. Scientists are very interested in discovering the biological signals that tell people they feel full. The formal term for feeling satisfied after eating is satiety. I think major discoveries about the sources of satiety are coming, and are going to win some Nobel prizes.”

While people who like sugar could evolve to have less of an advantage over generations due to the health effects of eating too much of it, it would take tens of thousands of years, Wooding explained to EcoWatch. He added that the health crisis isn’t all about sugar, it’s also caused by an increased consumption of complex carbohydrates, proteins and fats.

“Anyone who decides they want to reduce their sugar consumption is up against millions of years of evolutionary pressure to find and consume it. People in the developed world now live in an environment where society produces more sweet, refined sugars than can possibly be eaten. There is a destructive mismatch between the evolved drive to consume sugar, current access to it and the human body’s responses to it. In a way, we are victims of our own success,” Wooding wrote for The Conversation.

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A French scientist shows microplastic waste collected on the Aquitaine coast on the beach of Contis, southwestern France. Photo credit: MEHDI FEDOUACH / AFP via Getty Images

Microplastics — small pieces of plastic less than five millimeters long — are the most common type of debris found in the ocean, according to the National Oceanic and Atmospheric Administration’s National Ocean Service. But before they make it into the ocean, a new study has found that they can become stuck in riverbeds for up to seven years.

Prior to the study, researchers believed that the tiny, lightweight plastics flowed rapidly through rivers without becoming snagged on riverbed deposits, Northwestern Now reported. But the researchers found that when water on the surface of a river mixes with water from the river bottom, it can trap microplastics that might otherwise float, in a process called hyporheic exchange. The study, “Microplastic accumulation in riverbed sediment via hyporheic exchange from headwaters to mainstems,” by researchers led by Northwestern University and the University of Birmingham, was published in the journal Science Advances.

“Most of what we know about plastics pollution is from the oceans because it’s very visible there,” said Aaron Packman, a senior author of the study and a professor of civil and environmental engineering at Northwestern’s McCormick School of Engineering and director of the Northwestern Center for Water Research, reported Northwestern Now. “Now, we know that small plastic particles, fragments and fibers can be found nearly everywhere. However, we still don’t know what happens to the particles discharged from cities and wastewater. Most of the work thus far has been to document where plastic particles can be found and how much is reaching the ocean. Our work shows that a lot of microplastics from urban wastewater end up depositing near the river’s source and take a long time to be transported downstream to oceans.”

For the study the researchers developed a new model that describes hyporheic exchange processes and focused on microplastics 100 micrometers and smaller. The study is the first to examine the buildup of microplastics and how long they remain in rivers or streams, from the original source through the entire system.

“The retention of microplastics we observed wasn’t a surprise because we already understood this happens with natural organic particles,” said Packman, Northwestern Now reported. “The difference is that natural particles biodegrade, whereas a lot of plastics just accumulate. Because plastics don’t degrade, they stay in the freshwater environment for a long time — until they are washed out by river flow.”

The researchers found that the microplastics remained longest at the headwaters of a river or stream, averaging five hours per kilometer, Nature World News reported. But during low-flow periods, it could take as long as seven years for the plastic particles to move one kilometer. During these times, organisms in the waterway are more prone to ingesting the microplastics, degenerating the health of the ecosystem.

Microplastics reduced their residence time as they traveled downstream of the headwaters, staying the least amount of time in large creeks, according to Northwestern News.

“These deposited microplastics cause ecological damage, and the large amount of deposited particles means that it will take a very long time for all of them to be washed out of our freshwater ecosystems,” Packman said, as reported by Northwestern News. “This information points us to consider whether we need solutions to remove these plastics to restore freshwater ecosystems.”

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