LEDs are everywhere today. But what does L. E. D. stand for anyway?

Luminous Efficiency Device? Less Electricity Demanded?

Not quite – though both correctly describe Light Emitting Diodes. They make more light, from less electricity, than any other technology.

Incandescent bulbs of the 20th century heat a metal filament until it glows white hot. They produce light, but much more electricity is converted into, and wasted as, heat.

Fluorescent tubes pass energy through a gas that glows. They consume less electricity, but their light is not so attractive, they must be disposed of properly, and the bulbs can be fragile.

So scientists kept pushing for something better, and invented LEDs in the 1960s. The initial technology was basic and expensive, but worked the same way it does today:

Electricity flows through a two-layered semiconductor. One layer has an excess of negatively charged electrons.

The electricity forces electrons to jump to the other positively charged layer to equalize. As they do, they release a small amount of energy as light.

Multiply that over millions of electrons and these diodes can emit a great deal of light, with very little energy wasted as heat.

They’re such a step up over old bulbs, that LEDs now make up half of global lighting, and growing.

Have you ever wondered how squirrels find the nuts they hid months before?

A typical squirrel can store 3,000 of them in a fall season, in dozens of locations. It seems almost impossible that they could remember them. But they do.

There are 200 species of ground squirrel, tree squirrel and flying squirrel that rely on stored seeds and nuts.

To do that, they need to return to them even after leaves fall and snow covers the ground. How do they do it?

Smell plays a role. But sight and memory are more important.

Squirrels build a mental map of their surroundings: a tree trunk, a large rock, a fallen log, a fence post.

Then they remember the changing spatial relationships between those landmarks when viewed from their different food hiding places.

Some scientists have wondered if a squirrel’s brain grows to meet the season’s mental demands.

Because there are other rodents -- shrews, European moles and weasels – whose brains contract 10% in winter when food is scarce, then expand again in spring, with no impact on function.

But most research suggests a squirrel’s heightened spatial memory is linked to its larger than normal hippocampus, a part of the brain involved in learning and navigation.

They’ve also shown more neuron growth, and less age-related mental decline.

To fuel this acuity, squirrels require a lot of calories – which ironically means they must hide more nuts to help them find the others!

In 1985, a passenger jet landing at DFW airport was forced to the ground by an unusual downward blast of wind called a downburst. The plane struck cars on the highway and a water tank, then crashed on the airfield, killing more than 100 people.

It was the third such fatal crash in a decade. So, the FAA set out to invent a new warning system for these dangerous wind events. A downburst is a sinking column of air within a thunder cloud that accelerates toward Earth, reaching speeds over 100 miles an hour.

When it strikes the ground, it blasts out in all directions, like a mammoth version of water splashing in a sink. These winds are strongest just 10 to 30 feet from the ground and travel horizontally outward in all directions. They can fell trees like a tornado’s whirling winds, but they all fall in the same direction, like dominoes.

For aviation, the first step was training pilots to look for visual signs – expanding rings of dust on the ground below, or sharply defined shafts of intense rain.

Technologically things were more complex. Vulnerable airports installed a network of wind sensors, as well as advanced Doppler radar that could track wind speeds. All fed into an early alert system.

By 1994, 46 high traffic airports had installed these systems. They haven’t had a single downburst accident since -- and technology continues to improve. A triumph of aviation safety.

Sand is incredibly common. There are oceans of it – in oceans, and deserts too. But, for our purposes, that’s not the right kind of sand.

We use sand in concrete, to make bridges and roads, buildings, houses and power plants. We use it in glassmaking, for windows, computer chips, solar panels and much more. We use it for hydraulic fracturing, to prop open cracks in shale deposits so oil and gas can flow.

In all, we use billions of tons of sand every year. But only a certain kind will do.

Beach sand is often mixed with salt. If used in concrete, it can corrode the reinforcing steel. And the grains of beach sand, and especially desert sand, are often rounded by waves or wind. Concrete needs angular grains that lock together. Hydraulic fracturing needs hard grains that can withstand pressure. And glassmaking needs almost pure quartz.

That means, for most uses, the ideal sand is angular, well-sorted quartz. And that’s only found in a few places.

Rivers and streams are natural sorting machines. They break down and wash out weaker minerals, leaving quartz sand in bars and banks, which can be dredged or mined. Through time, many of these quartz sand deposits were lithified into sandstone, which today can be ground back into sand.

Our demand is so great that this once common material is becoming scarce, spawning a lucrative international trade -- for the right kind of sand.

Plastic has remarkable value to humans. But it’s also a major source of ocean plastic pollution.

Most of it is nets and rope from fishing boats, or municipal garbage that’s carried down rivers into the ocean. There it accumulates in spinning gyres of plastic, twice the size of Texas.

Large pieces eventually break down into fragments and microplastics. But because plastic is made to be durable, it won’t degrade any farther than that.

Wouldn’t it be great if we could clean it up?

That’s what a Dutch teenager thought when he was diving in Greece and saw more plastic bags than fish. He created a high school science project -- that has since grown into an international nonprofit, called The Ocean Cleanup, employing engineers, marine biologists and collection teams.

They set up huge U-shaped nets that float with the current in the spinning gyres, in the top few feet of water where most plastics (but few fish) are. These gradually capture the debris, which their boats collect and haul to shore.

They’ve also installed collection systems at the mouths of rivers to intercept plastic before it enters the ocean. Together, their systems have captured millions of pounds of plastic waste, which they sort, recycle or properly landfill.

There’s much more to do, but they’ve inspired governments and other nonprofits to work on plastic waste management on land and at sea.

Hopefully, with growing awareness, we can all make a meaningful difference in ocean plastic pollution.

In the mid-1800s, London’s SoHo neighborhood was a terrible smelling place to live, as raw sewage ran through the gutters into open cesspools.

When a cholera epidemic broke out, 600 people died and many remaining residents fled, fearing – as was common then – that foul air spread the disease.

Local physician John Snow didn’t buy it. Ten years earlier, he had proposed that cholera spread through contaminated water. But lacking proof, he was ignored.

With an outbreak on his doorstep, he saw an opportunity to test his hypothesis – and save his neighborhood.

First, he obtained the addresses of every person who had died. Then he walked the streets plotting the deaths, and everything else, on a map.

Soon a pattern emerged. Most of the cases clustered around one public water well.

He began interviewing area residents. Locals with their own private wells had not gotten sick. Workers at a nearby pub, who drank a daily ration of beer instead of pump water, were also spared.

Snow convinced local authorities that water from the well was to blame, and persuaded them to remove the pump handle, forcing residents to draw their water elsewhere. Immediately the cholera outbreak ended.

With his cholera map, Snow had begun the field of evidence-based epidemiology. This was well before germ theory and microscopes could identify the true culprit, the cholera bacteria, that had spread through sewage leaking into the water supply.

A large manatee can top 1000 pounds and eat 15% of its weight in seagrass each day.

That may sound hardy, but manatees are actually very sensitive. There are three species, all adapted only to the constant warm waters of the tropics.

But the West Indian manatee has found a way to survive Florida winters by taking advantage of the state’s geology.

As temperatures drop, manatees leave coastal waters and swim up rivers toward headwater springs.

Florida has hundreds of springs, more than any other state, and some are huge, pumping out millions of gallons a day.

The springs are fed by rainwater that percolates through Florida’s limestone bedrock, flows underground, is heated by geothermal energy, then emerges to form warm, clear pools that feed rivers.

The spring pools are home to large ecosystems of many species -- including, in winter, manatees, who come by the hundreds to spend the cold months lounging, and eating.

Like so many things in nature, the springs are under pressure from human development. Florida cities and agriculture pull water from the aquifer, reducing flow into the pools. Fertilizer seeps into the groundwater and enters the springs, clogging them with algae.

Despite that, the manatees’ numbers are increasing, due to conservation efforts by Florida preservation groups. A success story of shared resource use that can hopefully sustain these remarkable creatures long into the future.

Is there life on Mars? That’s the question NASA wanted its first Mars mission to answer – in 1976.

They designed their remarkable Viking rover -- well before modern computers -- to collect and test soil samples, 140 million miles from Earth.

First, Viking added a nutrient solution to the soil, looking for carbon dioxide that microbes would produce if they consumed it. And the test showed a small amount!

Next, Viking incubated the sample to see if microbes, if present, could produce organic matter. A tiny amount was detected!

But the third test would be conclusive. The rover incinerated the soil to gasify its compounds, then used a spectrometer to evaluate them. If there were organic matter, it would surely show up. But it didn’t.

At the time, the answer was: no life on Mars.

Several decades later, subsequent missions, using different tests, did find signs of microbial activity. So NASA went back to review the Viking data.

With 50 years of new understanding, many scientists now believe that salt compounds in the Martian soil, when heated, would have destroyed any organic matter. Meaning Viking’s gas test may not have been designed or understood correctly.

Today, there’s still no solid proof that Mars has microbial life. But new -- and half-century old -- tests haven’t ruled it out either!