EarthDate

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!

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.

Rust is common on Earth. It shouldn’t exist on the moon. But somehow, it does.

Rust is just the common name for iron oxide. Iron that has bonded to oxygen.

The moon, however, has no oxygen. Yet lunar rovers have recovered grains of iron oxide in lunar soil. How could they have gotten there?

One possibility is from Earth. Or rather, from our atmosphere.

The magnetic field of our planet, called its magnetosphere, surrounds Earth like an invisible force field.

The sun produces a solar wind of charged particles that flows outward into the solar system.

When it encounters our magnetosphere, it deflects around Earth. The charged particles flow around us and deep into space, in a so-called magnetotail that stretches three million miles behind Earth.

As the charged particles pass, they strip off some oxygen ions from the upper reaches of our atmosphere, and carry them into the long magnetotail.

Each month during the full moon, Earth is between the moon and the Sun, which may shelter the moon from solar wind, and bathe it in oxygen from Earth’s magnetotail.

Scientists believe that when these oxygen ions strike the moon’s surface, they bond with iron in the lunar soil to form, yes, tiny particles of rust.

This is still a hypothesis. But it’s important because it highlights how little we know about our closest celestial neighbor… where humans might soon spend a bit more time.

Imagine there was not one species of human…but many. One stronger. One smaller. All different, but closely related.

Around 40,000 years ago, that’s exactly how it was. Homo sapiens – us – shared Earth with several other Homo species. Then those other ones went extinct, and we carried on. The sole survivors.

Why? Because we could better adapt to changing climates. And that’s because of a few key qualities.

First, we had more flexible diets. We could eat large animals or small. Fish, fowl, or foraged plants.

One reason we could do that, is we also had better control of fire. Which allowed us to cook those various foods to extract more nutrients and calories.

We also had better tools, to more effectively butcher animals, and importantly, sew their hides into fitted clothing and covering for shelters -- which allowed us to endure the bitter cold of the Ice Age.

And because of those things, we were mobile. We could take our tools, clothing and shelters, flexible diets and fire to cook them, to different regions as climate patterns changed.

We also had dogs, for hunting. And to hear that amazing story, look it up on EarthDate.org.

But there’s one more Homo sapiens trait that may have mattered most of all. We had advanced language, to communicate the knowledge of all these things, to cooperate and collaborate, and to build the social cohesion required to weather difficult environments.

Gold is rare. Except in one place on Earth that it’s incredibly plentiful. But we’ll probably never get to it.

Over the course of human civilization, people have searched for gold. Still, we haven’t found much – 220,000 tons across all those centuries. By comparison, we’ve mined seven times as much silver. And 3,000 times more copper.

But we now know there’s much, much more gold on Earth.

When the planet formed, more than 4 billion years ago, many metals swirled together in Earth’s molten magma, gold among them. Being heavy, it was pulled toward the center, into Earth’s core, by the force of gravity. There it bonded with abundant iron. And there it has mostly stayed.

But Earth’s interior is not static. The molten magma sometimes upwells toward the surface.

Over millions of years these magma currents have carried small amounts of gold and other metals out of the core.

Earthquakes and shifting tectonic plates then brought that magma toward the surface. Some of it precipitated out in veins, which we have mined. And some of that eroded into rivers and streams, and we gathered it there too.

Because it’s valued, and doesn’t oxidize, most of the gold we’ve found over the years still exists in pure form and gold-rich alloys, and is still in use – in jewelry, art, electronics, even medicine.

It may be precious, but it’s not scarce. It’s just that Earth has limited our access.

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!

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.

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.

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.

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.