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.