When scientists mapped the human genome, they found that just 2% of it controlled our own functioning. Fully 8% was the DNA of fossil viruses.

Paleovirologists who study fossil viruses have found that all viruses share a common single-cell ancestor from more than 3 billion years ago.

About 1.5 billion years ago, viruses changed their protein coating, allowing them to penetrate the cells of their hosts.

As multicellular life became increasingly complex, viruses got simpler, eventually giving up independent life. They threw out genes they didn’t use and discarded their means of reproduction until they were totally reliant on cell hosts.

When a virus enters a cell, part of its RNA is converted to DNA within the cell’s gene code.

If that cell is an egg or sperm, that DNA could be passed to the next host individual.

However, that can only happen if the virus does not kill the host.

So, if the virus is beneficial or benign—or if the host’s immune system is able to defeat it and become healthy enough to reproduce—then the viral DNA can be passed down through generations.

This process has occurred enough times over millions of years for viral DNA to make up that 8% of our gene code.

And fossil viral DNA has been very beneficial to us and all other organisms, as we’ll discuss in another EarthDate.

Dr. Gene Shoemaker mapped the moon, trained astronauts and discovered more than 800 asteroids. He was also the first person to go to the moon… and stay there.

Shoemaker started his career with a bang, proving with his Princeton dissertation that the mile-wide Barringer Crater in Arizona, previously attributed to volcanic activity, was in fact the result of a meteorite impact.

Soon after, he founded the astrogeology program of the U.S. Geological Survey, in part to better understand the potential threat of future meteorites.

He led a team to map the craters of the moon, then was called to advise the Apollo space program, training its astronauts for their lunar geological surveys.

He and his wife Carolyn co-discovered the Shoemaker-Levy 9 comet and predicted its impact with Jupiter, which the world watched through the Hubble Telescope.

At 64, he received the National Medal of Science, capping a career of awards.

At 69, while exploring a meteorite crater in Australia, Shoemaker’s life was cut short in a car crash.

He often said his one regret was not going to the moon to experience its geology himself. So NASA decided to grant his wish.

They placed a small capsule of his ashes inside the Lunar Prospector research spacecraft. It orbited the moon for 18 months of exploration, then deliberately crash-landed into a lunar crater where Shoemaker is now interred, the first human remains on the moon.

To Egyptians and ancient Greeks, amethysts were as precious as diamonds, rubies, and sapphires.

The stone was thought to cool tempers and prevent drunkenness, so it was cut into jewelry for wise kings and crafted into wine goblets for those who hoped to stay sober.

In the Middle Ages, it adorned the rings of religious leaders and the scepters of royalty.

Since then, huge finds in many places, especially Brazil and Uruguay, have made amethyst plentiful and affordable.

And that’s good, because this brilliant purple gem is now available to everyone and is still just as striking.

Especially when you consider that amethyst is just quartz with a few special qualities. It has trace amounts of iron, only a few parts per million.

These would normally be invisible, but when exposed to gamma rays, they make the quartz turn purple—into amethyst.

It doesn’t take a lot of radiation; it’s naturally occurring in other rocks found where amethyst crystals grow, and not nearly enough to be harmful to humans.

Amethyst’s color can change when exposed to other kinds or radiation. Enough UV radiation from sunlight will fade it to lilac or gray.

And it can change color when heated, turning light green, yellow, or brown… though another dose of the right radiation can bring back its purple hue.

Amethyst is the February birthstone, so if you know anyone born in this month, try giving them a birthday gift that was once the stone of sober kings.

You might have heard of your microbiome, but did you know you also have a virome? That’s right, there are more than a trillion active viruses within you right now.

Viruses exist in every organism, in every environment. There are at least ten times more viruses on Earth than all other biological entities combined.

A virus is a tiny packet of RNA or DNA, about 1500 times smaller than a grain of salt.

They lack the ability to reproduce or the ribosomes to make energy. Many scientists don’t even consider them to be alive. They can only flourish within the cells of their hosts.

When a virus enters a cell, its genetic code instructs the cell to replicate it. Not really reproduction, but duplication.

When the cell is spent, it releases these newly created viruses to repeat the process.

Most viruses are symbiotic and beneficial to the host.

Some attack bacteria, as in our gut. Some provide genes the host can use, like those that protect plants from drought or cold. Others leave behind bits of genetic code that have helped hosts evolve, something we talk about on other episodes.

Pathogenic viruses harm or kill the host, but there are only about 200 that infect humans, like the coronaviruses that cause the common cold and COVID-19.

Though these rogue actors have given viruses a bad name, the truth is, we couldn’t live without our friendly virome.

In another episode, we talked about the horseshoe crab, which has existed on Earth nearly unchanged for more than 400 million years. In the last 40 years, it’s become a vital player in our medical industry.

Why? It’s in their blood.

Horseshoe crab blood is copper based, not iron based like ours, which makes it blue.

It coagulates so rapidly and completely around invading pathogens, that medical researchers realized it could be used to detect pathogens for us too.

So they isolated the coagulating agent, called LAL, powdered it, and now use it to test every vaccine, intravenous drug, and medical implant for the presence of bacteria in every hospital and lab around the world today.

To get enough blood to produce the LAL, medical companies capture half a million horseshoe crabs each year when the creatures congregate for spawning. They drain about 30% of their blood and then release them.

This procedure, along with human beach encroachment and increased fishing pressure, is reducing horseshoe crab numbers worldwide.

Scientists have responded by creating a synthetic substance similar to LAL, which is starting to replace the original, and with breeding programs to rebuild populations.

If you ever find a horseshoe crab on a beach, you can lend a hand. Pick it up by its shell—never by its tail, which can harm it—put it back in the water, and thank it for its service to humans.

The horseshoe crab is a living fossil—sometimes called a stabilomorph, a body design that evolution got so right, it hasn’t had to change.

They’ve been roaming the coastal shelves and brackish bays of Earth for more than 400 million years in nearly the identical form as today, having survived all five great extinction events we’ve discussed on EarthDate—including the asteroid that wiped out the dinosaurs.

Why are they so enduring? A few reasons:

They’re generalists that can live in shallow or deep, warm or cold water, and eat pretty much anything they find on the sea floor.

They breed very successfully, grow fairly quickly, and have long lives—typically 20 to 40 years.

And they’ve developed a unique and powerful immune system to keep them healthy.

Horseshoe crabs live in bacteria-rich environments yet have a primitive open circulation system that can be prone to infection.

So their blood—actually a blood-like substance called hemolymph—developed special cells that release granules when they detect even the tiniest concentration of pathogens or the toxins they can produce.

The granules cause the blood to coagulate into a gel around the intruders, trapping them and sealing them off from the rest of the crab’s system. It’s so effective, it can close off the wound from a lost limb, sealing out bacteria.

This capability has made the lowly horseshoe crab absolutely invaluable to human medicine, which we’ll discuss in another EarthDate.

What if you’re a fish in freezing water?

Well, a free-swimming ocean fish can migrate to a warmer part of the sea.

But if you’re a lake fish, you don’t have that option. Luckily, the properties of water make its solid form—ice—less dense than its liquid form.

As a lake freezes, the ice floats on the surface, insulating the water below and keeping most lakes—and the fish within them—from freezing solid.

You would still, however, be very cold. Lake fish have to lower their metabolism and enter a state called torpor to reduce their energy demands enough to survive the winter.

This is especially important in spring before the ice melts, when oxygen levels in the water trapped under the ice may be dangerously low.

And what if you’re the unlucky fish where it’s even colder? Fish in polar regions live in saltwater that’s around 28 degrees Fahrenheit—that’s below the freezing point of fish blood.

In that case, you’d need antifreeze in your veins. And polar fish have developed exactly that. They produce a glycoprotein that slows down water’s molecular motion to keep ice crystals from forming.

All pretty interesting if you’re a fish. But what if you’re not?

Medical researchers—and car makers—have teamed up to study fish antifreeze, looking for better ways to keep radiators from icing up and ways to keep human blood and tissue from being damaged by ice crystals when in deep storage. Pretty cool.

You’ve probably heard that no two snowflakes are alike. And mostly, that’s true.

Snowflakes aren’t formed from freezing water, but when water vapor freezes, skipping the liquid stage altogether.

This allows the water molecules to organize themselves into the snowflake’s delicate structure.

Snow crystals come in more than 30 basic shapes, with the classic star-shaped snowflake forming best in temperatures around 5 degrees Fahrenheit.

These begin when water vapor freezes around a nucleus like a dust particle. This forms a single hexagonal ice crystal, which is heavier than air and so begins to fall.

As it does, the ice crystal grows. The original hexagon sprouts hexagons on each corner. These grow hexagons on their corners. And so on.

But the exact form that the growing snowflake takes is influenced by changing humidity and temperature levels in the air it falls through.

And because no two flakes follow the exact same path from sky to Earth, no two grow in the exact same conditions, and therefore no two are the same.

The only exception is when scientists make them in a laboratory, where they can control the conditions so precisely, they can produce identical flakes.

So if you find yourself out on a snowy day, take a moment to marvel at the thousands of snowflakes you can see falling, the millions in your yard, or billions in a field. Like people, no two are or ever will be the same.

Each winter in the Northern Hemisphere, it feels like Earth is drifting farther away from the warmth of the Sun.

In fact, it’s just the opposite. When we measure the size of the Sun in our sky, we find that it actually appears 3.4% larger in winter—because it’s 3.4% closer.

More than 3 million miles closer. The Sun is about 95 million miles away in summer, but just 92 million in winter.

And this is because Earth’s orbit is elliptical, with Earth following the closer part of its path during the northern winter.

You’d expect the nearer Sun to provide more solar energy to our planet and you’d be right: almost 7% more.

But its effect is greatly minimized by the 23-degree tilt of Earth’s axis, turning the Northern Hemisphere away from the Sun in the winter.

At the same time, in the Southern Hemisphere summer, that extra solar energy is mostly absorbed by the huge southern oceans.

The effects may be minor today, but that won’t always be the case.

The gravity of Saturn and Jupiter pulls Earth through a long cycle of orbital stances, from nearly circular, to more elliptical.

We’re now as close to circular as our orbit ever gets. In about 200,000 years, we’ll be at our elliptical maximum.

Then, Earth will receive 23% more solar radiation when closest to the Sun. This varying solar energy will have significant impacts on weather and climate.

How long is a second? That depends on how you measure it.

In a previous EarthDate, we talked about how people divided the day into 24 hours, then hours and minutes into 60. That made the second 1/86,400th of a day.

But how long is a day? Turns out, that’s not constant. Earth wobbles slightly on its axis, changing its rotation time.

So scientists settled on a year, reasoning the day’s length would average out.

But which year? Those aren’t constant either.

So they agreed on a specific year: 1900.

A second then, was measured as 1/31,556,925.9747th of the year 1900. Not a very elegant solution.

So scientists looked for a new measurement.

They found an isotope that changes magnetic orientation when, and only when, it’s hit with microwave energy of a very specific frequency.

This relationship was so stable, and the procedure so repeatable, that they used it to set the new standard of time: 1 second equals 9,192,631,770 cycles of the microwave energy that switches the atomic state of cesium-133.

That may not be any more elegant. But it is very precise—down to the nanosecond.