Every 11 years, the Sun cycles from solar minimum to solar maximum, as we discussed in a prior EarthDate. And we’ve just entered another solar maximum, where the Sun emits many more charged particles in a faster, stronger solar wind moving toward Earth.

You might experience it in disrupted GPS or cellular signals. But you can see it in the night sky. Specifically, in the aurora borealis, the famous northern lights.

You may remember, also from a prior episode, that Earth’s magnetic field shields us from the charged particles in the solar wind, allowing life on Earth.

Some particles still get through but are directed by the magnetic field around Earth toward its magnetic poles.

These particles excite atoms in the atmosphere, which emit light. Oxygen emits mostly green light, and nitrogen red. They blend together in unusual ways to create many colors including blue, purple and pink.

With stronger solar winds, more charged particles will get through, meaning brighter auroras that will be more visible, even at lower latitudes like the Midwest United States.

But they’ll still be the most visible within 30 degrees of the magnetic poles, when the pole is farthest from the Sun, around midnight. And particularly around the spring and autumn equinox.

So for your best shot at a spectacular nighttime light show, head to the Arctic Circle in mid-September. Maybe I’ll see you there.

Last EarthDate, we talked about the eruption of Mount Vesuvius, which completely covered Pompeii in ash. Within a century, the city was forgotten.

Until the 1500s, when an architect dug into a room. It had once been a brothel, with explicit frescoes on the wall. Considering them inappropriate, he buried them again.

In the 1700s, artifacts were discovered in a vineyard in the volcanic soil above the buried city. So began 250 years of excavation. 

In the 1800s, archaeologists discovered strange voids in the pumice. They realized they once contained bodies, frozen in their final positions, and filled them with plaster to cast the human forms.

The city, too, had been frozen in time, yielding a stunning account of Roman civil life.

Pompeii had busy avenues, a marketplace, courts and municipal buildings and a water supply system.

It had architects and engineers, carpenters and jewelers, innkeepers, shopkeepers and over 200 bars and restaurants.

In some, food was even preserved, including bread from more than 30 bakeries. Pompeii even had a 20,000-seat gladiator arena for local and regional spectators.

And with temples for Greek and Egyptian gods, and ads in Hebrew on walls, it seems Pompeii drew travelers from far and wide.

A shame it was destroyed … yet fortunate it was so well preserved.

For millennia, people have been drawn to volcanoes.

Why? Because before they arrived, the volcanoes had erupted.

Their lava, ash and debris covered the surrounding area, making for fertile farmlands that drew settlers … who may not have recognized that the volcanoes could erupt again.

And that’s just what happened around Italy’s Mount Vesuvius. Long before the Romans, people had come to farm there. When Rome eventually controlled the region, inspired by the pleasant climate and bountiful agriculture, they named it Campania Felix—the happy, fertile countryside.

One of the happiest towns was Pompeii, a popular vacation spot of the day. But Mount Vesuvius would change all that.

In AD 62, it sent earthquakes through the region, displacing residents. Most had returned when, 17 years later, Vesuvius erupted.

First, it blasted a spire of ash and pumice 10 miles into the sky. This rained down on Pompeii, leaving a layer 8 feet thick. Most citizens fled, but 2,000 remained, sheltering in stone houses and cellars.

The next day, clouds of burning hot toxic gas flowed down the mountain, instantly suffocating residents. More ash rained down, encasing the victims in their final positions.

Their tragic end, however, would be a great boon to historians centuries later – which we’ll discuss in the next EarthDate.

In the beginning, Earth was hell.

The planet was completely molten, a roiling sea of magma at temperatures of thousands of degrees. Scientists even referenced Hades to name this period: Hadean Earth.

How did it become the green paradise we know today? Well, over about half a billion years, it cooled. And how it cooled has shaped some important traits of Earth to this day. Logically then, scientists are studying what happened.

They use seismic waves from natural earthquakes and man-made explosions to map today’s inner Earth. And they’re using theoretical modeling to study its ancient past, which suggests that Earth cooled like this:

Very hot surface material, in contact with an early atmosphere, began to cool first.

Convection currents carried warmer magma from Earth’s center up toward the surface and forced cooler material back down.

Metals and elements attracted to iron sunk out of the current to form a central iron and nickel core.

The mantle between surface and core began to cool next, while the lowermost mantle remained liquid.

Scientists think this basal magma ocean had strong fluid currents within it, which may have converted kinetic energy into electromagnetic energy. This could have helped start Earth’s geodynamo—which today generates Earth’s magnetic field from its metal core.

But as with all science, this research is ongoing—so expect updates on a future EarthDate.

You might think that plants are stationary, but did you know they can dance?

Many flowers do a daily sun dance, swinging from east to west, to produce more pollen and attract insect pollinators.

They make this movement using two methods:

Plants contain a compound called phototropin that responds to being in shadow by causing cells to elongate. In this way, the dark side of the plant grows longer, which curves the other slower-growing side toward the light.

All plants do this, but the sunflower is special. It can elongate its cells every minute!

Each day as the Sun moves westward, cells on the east side of the stem just beneath the flower grow, tilting the flowerhead westward to follow the Sun. At night, the west side grows, pushing the flower back toward the east to greet the morning sun.

The sunflower will do this daily dance until fully mature, when it stops growing, usually with the head facing east.

Other plants in the sunflower family, like daisies and dandelions, can also follow the Sun, but use a different method. They pump potassium and water across cell membranes to inflate or deflate cells, thereby bending the stem.

Using these methods, many plants can change their orientation, not only to light, but moisture, gravity and other stimuli.

Not exactly dancing, but moving in rhythm more than we might think.

In 1797, in central Kentucky, a hunter chased a bear into a hole in a cliff … and discovered the longest cave network in the world, 10 million years in the making.

But at that time, all he could see—and smell—was bat guano, which was then the valuable source of saltpeter, a key component in gunpowder.

Within a year, prospectors were mining centuries of bat droppings for military efforts. During the War of 1812, the gunpowder business boomed, and so did the cave’s mine. In 1815 the war ended, and so did the mine.

The next year, Mammoth Cave, named for its enormous size, opened as a tourist attraction. The slaves who had been the miners now served as tour guides.

They showed the cave to Gilded Age patrons, who carried oil lamps and used their smoke to write their names on the ceiling.

In the 1840s, a freed slave named Stephen Bishop, an expert cave guide, was the first to explore and map the cave.

After a century of tourism, it was thought to comprise more than 40 miles of caverns and connected passages.

But new scientific exploration and technology, continuing to the present day, has revealed it’s actually 10 times that size. And more rooms are expected to be found.

Today, the cave’s petroglyphs and speleothem formations are seen by half a million visitors a year. If you find yourself in Kentucky, be one of them!

For nearly 60 years, an international deep ocean drilling program has revolutionized earth science and understanding.

Two research ships in particular, the Glomar Challenger, later replaced by the JOIDES Resolution, have drilled hundreds of miles of ocean sediment core, in every ocean. These cores provide a record of Earth stretching back millions of years.

They’ve allowed scientists to validate the theory of plate tectonics, study ancient sea creatures, climate and sea level fluctuations, past earthquakes, volcanoes, asteroid impacts, changes in Earth’s magnetic field and more.

And they’ve furthered science in monumental ways. They’ve helped us build the geologic time scale. Make the link between natural orbital cycles and long-term climate variability. Map global ocean circulation patterns to better understand how they warm continents and influence weather.

They’ve shown us that the Mediterranean Sea has completely dried out, several times, and that the Arctic was once subtropical, abounding with warm-water life forms.

They’ve discovered frozen natural gas beneath the seafloor, along with the sunken continent of Zealandia.

In September 2024, the Resolution will be retired, after almost 40 years of service. Smaller European and Japanese ships will keep on drilling, while hopefully the U.S. builds another flagship, to continue the scientific discovery vital to human progress.

Sharks have been so successful, for so much longer than so many other lifeforms, that you could call Earth the shark planet.

They evolved over 400 million years ago, meaning they’re older than trees. They’re 6 times older than the North Star! And over a thousand times older than humans. They’ve survived all 5 known mass extinction events.

Over that long, long period, they’ve diverged into hundreds of species and adapted to every marine environment from deep oceans to estuaries.

And they’re magnificent creatures: sharks recover from injury and heal quickly. They almost never develop cancers or get heart disease. And they’re immune to infections. Some species, like the Greenland shark, can live more than 400 years.

Sharks are essential to the health of Earth’s oceans, culling sick and weak fish and scavenging dead ones. But today, they’re in great danger.

Sharks mature and reproduce slowly, so they don’t adapt quickly to environmental changes.

While they’re highly efficient predators, they have almost no interest in humans—we’re not their natural prey.

But they’re often killed by fishermen. And their numbers are declining from overfishing, mostly for shark fin soup. Eighty million are caught each year, often their fins cut off while alive, then they’re thrown back to die.

Instead of killing them, we should admire and protect one of Earth’s oldest and most well-adapted animals.

If left unprotected, something made of iron will dissolve into dust. That’s because of rust.

Some metals, like gold and platinum, are naturally stable and keep their shiny appearance.

Other metals like aluminum, copper and silver develop patina or tarnish that protects the raw metal beneath.

Iron is different. It’s the most abundant element on Earth, followed by oxygen—together they make up over 60% of all elements. And they like to get together:

Almost all iron on the surface of Earth appears as an iron oxide—a mixture of iron and oxygen.

We smelt iron oxides to get pure iron, which we use as a metal or blend into alloys like steel. But once it’s been separated from oxygen, it wants to bond again.

When water gets involved, rust forms.

It’s not well defined as a chemical process, but initially the iron oxidizes, then water turns that molecule into a new compound we call rust, which replaces the metal.

And because the rust molecule is larger, it doesn’t fit in the same place and flakes off as rust. This exposes new metal, which will rust and flake off—until all the iron is gone.

With so much of our buildings, bridges, pipelines and other infrastructure made of iron or steel, it’s important to keep them oiled, painted, coated or alloyed to be protected.

Because as Neil Young said, rust never sleeps.

Drinking salt water is poisonous to humans. It’s four times saltier than our blood, so our kidneys pull water from our tissues to try to balance the seawater, which could lead to dehydration or death.

Whales and dolphins, seals and walruses are all mammals, and they need fresh water too. But they live in salt water. So what do they drink?

Nothing! Their digestive systems are superefficient at pulling all the fresh water they need from their food.

What about fish? They need water too. You’d think this would be no problem for freshwater fish.

But because their blood is more salty than the water they live in, they have to be careful not to drink it. When water goes in their mouth, they push it out through their gills, where the right amount of water is absorbed through osmosis.

For saltwater fish it’s a different story. They get their fresh water by drinking salt water. They have special kidneys adapted to filter out and expel the salt.

Scientists thought that highly venomous sea snakes also drank seawater and expelled salt. To test that, they captured a hundred of them before and after a rain.

Those caught before the rain drank fresh water offered to them—they were thirsty. Those captured after the rain had no interest in water. The scientists realized they drank rainwater, which being less dense, floats on the surface of the salt water.

All creatures require water to live. Even those living in water!