Previously we talked about how early humans outcompeted Neanderthals. One big reason for their success might be sitting right next to you. I’m talking about dogs.

When humans arrived in Europe, they were at the top of the food chain, along with Neanderthals, big cats, bears—and wolves.

Archaeological records suggest that humans soon began to domesticate wolves, which quickly evolved into proto-dogs, and joined the hunt.

The dogs did what they did best—chasing large prey over distance, tiring and cornering them. Man stepped in with spears and arrows to close the deal, sparing dogs the dangerous part of the kill. Then they shared the meat.

Butchering sites for large animals like mammoth would have attracted other carnivores. Scientists believe early dogs also helped keep scavengers away.

Fossilized remains show early dogs were similar to huskies, but bigger. The skeletons show healed broken bones, suggesting a rough hunting life but also care afterward.

By contrast, Neanderthal sites show no evidence of a partnership with dogs.

Humans and dogs became such a dominant hunting force, researchers believe, that they simultaneously eliminated large prey and outcompeted not just Neanderthals but most other large predators.

So the next time you see a dog, give ‘em a big “thank you” belly rub.

They were essential to human success. And with that, they guaranteed their own—and a friendship lasting 50,000 years.

Previously, we talked about how scientists discovered the asteroid that brought down the dinosaurs.

But what exactly happened when a rock twice the size of Manhattan smashed into our planet— with the force of 10 billion atomic bombs?

It punched a hole in Earth’s crust 50 miles wide and 20 miles deep, causing nearly a million cubic miles of solid rock to behave like liquid.

Like when a rock lands in a pond, the sides of the crater splashed outward, up, then collapsed. The center of the crater rebounded, rocketing up higher than Mount Everest; then it, too, collapsed.

Earth’s crust rippled like the surface of water. A ring of ridges spread out from the impact site.

This giant “splash” on Earth’s surface happened in a matter of minutes. Then, the rocks froze into their new positions and were protected from erosion by layers of marine sediment.

A 2016 mission drilled into the ridges circling the crater floor. The explorers found large sections of melted rock.

Below that, they found granites so badly pulverized that they were less dense than normal granite.

And, as often happens in science, one insight leads to another.

A recent space mission had discovered that the moon’s crust is less dense than it should be, and scientists wondered why.

The crater on Earth suggests it’s due to 4 billion of years of impacts on the moon’s famously cratered surface.

Today you can take a train, in a tunnel beneath the English Channel called the Chunnel, from London to Paris in 2 hours.

But half a million years ago, the English Channel didn’t exist: Britain was attached to Europe.

At that time, Earth alternated between glacial and interglacial periods, as it still does today.

During glacial periods, some of Earth’s water is held in vast glaciers, on top of continents rather than in oceans, which causes ocean levels to drop hundreds of feet.

Toward the end of one of these glacials, as the ice sheets started to melt, an enormous lake formed in the North Sea—dammed in the north by a massive wall of ice and in the south by a rock land bridge.

Eventually water levels rose so high that the lake began pouring over the British land bridge in gargantuan waterfalls.

Engineers planning the path of the Chunnel discovered this. Using seismic studies, they found huge, deep pits in the seafloor filled with rubble and sediment, and designed the Chunnel to avoid them.

Eventually scientists collected enough data to recognize the pits as plunge pools that those giant waterfalls would have made from millions of tons of water, pounding down on the seafloor over centuries.

The waterfalls began to erode the land bridge, but it held—until, a couple of glacial and interglacial cycles later, another flood finished the job.

The channel formed—causing a natural Brexit thousands of years ago.

Sixty-six million years ago, three-fourths of all species on Earth died out. Scientists knew it. But they didn’t know why.

Then, in the 1970’s, geologist Walter Alvarez and his physicist father Luis found a layer of unusual clay corresponding to the time of the extinction.

They discovered it contained a high concentration of iridium, a metal that’s very rare on Earth: it comes only from meteorites.

This intrigued other scientists, who looked at rocks from the same geologic horizon in different locations—and found more iridium. They began to suspect that a massive impact may have caused the mass extinction.

In the Caribbean, the clay layer was far thicker. If an event had happened, it must have been nearby.

Decades earlier, the Mexican state oil company had drilled exploratory wells on the Yucatan peninsula, west of Cancun. Rather than oil, they believed they’d hit a buried volcano.

So the scientists reexamined those samples and found the rocks weren’t volcanic after all, but showed signs of a profound impact.

They turned to modern aerial surveys and satellite images, which revealed an enormous circular feature with sinkholes lining its rim.

And they knew they had found it! Directly across the Gulf of Mexico from New Orleans was an ancient impact crater 125 miles in diameter.

This was where an asteroid struck Earth, ending the rule of the dinosaurs.

Previously, we talked about how scientists discovered the asteroid that brought down the dinosaurs.

But what exactly happened when a rock twice the size of Manhattan smashed into our planet— with the force of 10 billion atomic bombs?

It punched a hole in Earth’s crust 50 miles wide and 20 miles deep, causing nearly a million cubic miles of solid rock to behave like liquid.

Like when a rock lands in a pond, the sides of the crater splashed outward, up, then collapsed. The center of the crater rebounded, rocketing up higher than Mount Everest; then it, too, collapsed.

Earth’s crust rippled like the surface of water. A ring of ridges spread out from the impact site.

This giant “splash” on Earth’s surface happened in a matter of minutes. Then, the rocks froze into their new positions and were protected from erosion by layers of marine sediment.

A 2016 mission drilled into the ridges circling the crater floor. The explorers found large sections of melted rock.

Below that, they found granites so badly pulverized that they were less dense than normal granite.

And, as often happens in science, one insight leads to another.

A recent space mission had discovered that the moon’s crust is less dense than it should be, and scientists wondered why.

The crater on Earth suggests it’s due to 4 billion of years of impacts on the moon’s famously cratered surface.

Alchemists in the Middle Ages were fixated on turning lead into gold.

Both are soft, heavy metals. If they could make the dull one into the shiny one, they’d be rich. Right?

Maybe not.

Thousands of years before them, another metal, iron, was eight times more valuable than gold. It could only be found in its pure metal form in iron meteorites. Assyrians and Egyptians made prized iron jewelry, which we find in ancient tombs.

Then some alchemist of their time figured out how to smelt iron from common iron ore, like hematite and magnetite.

When supply boomed, the price plummeted. Iron eventually became the least expensive metal on Earth.

That’s because iron, as found in ores, is our most plentiful element by mass.

Iron makes up most of Earth’s core, which produces Earth’s magnetic field, protecting us from cosmic rays and solar wind.

Iron is the main ingredient in steel, an alloy of iron and carbon. We make a billion tons a year, and use it in everything, especially large buildings—which might be impossible without steel.

Iron is also abundant in the human body; it carries oxygen in the blood and gives blood its signature color…along with many other red things on Earth, from rocks and soil to farmers’ barns, painted with iron oxide pigments.

Iron is common and cheap and incredibly useful, so in some ways, that still makes it a lot more valuable than gold.

The Kingdom of Egypt prospered for 3,000 years—in the desert. Its success depended on strong leadership, written language, mathematics and engineering… but most importantly, on the flooding of the Nile, which happened each June through September.

Farmers developed an irrigation system that trapped floodwaters in their fields using dams. They let the water recharge the soil for a few months while the organics settled out, providing nutrients to the earth.

They’d then release the water to the receding river and plant their crops. In this way, year after year, the fields could produce enough food to sustain a large population living in the desert.

The floods were the direct result of African monsoons, which fell on the highlands of Ethiopia, the headwaters of the Nile. If the rain didn’t fall, the Nile wouldn’t flood. And there were some years that it didn’t.

Volcanic activity in the region filled the atmosphere with ash and gas, reflecting the sun’s heat, reducing evaporation and, therefore, rainfall.

Geologic and historical records now allow us to closely correlate volcanic eruptions with reduced Nile flooding, reduced crop production, reduced tax revenue for the state, and higher incidence of famine and revolt from the populace.

Especially high volcanic activity in the last 300 years of the Egyptian Kingdom contributed to its eventual fall to the Romans.

Yet another example of how connected human civilization has been, and continues to be, to freshwater supply, weather patterns, and the geology of Earth.

On other EarthDates, we talked about how humans have used, and sometimes overused, water from aquifers—to grow crops or build cities where previously none could exist.

It might surprise you to know there are also many places where we’re putting water back.

This aquifer management takes many forms.

Perhaps the simplest is called conjunctive use. That means providing surface water, during wet times, to users who would normally pump groundwater.

Another method is called managed aquifer recharge. It routes surface water into man-made or natural infiltration basins, where it can gradually seep into the aquifer.

Perhaps the best example of this channels floodwater away from population areas and into recharge ponds.

Surface infiltration has the added benefit of purifying the water as it percolates through layers of soil and rock.

In the most elaborate method, called aquifer storage and recovery, water is pumped directly into aquifers to stabilize or reverse groundwater depletion.

It has been used in coastal areas to stop saltwater from gradually entering aquifers and replacing freshwater.

Long-term studies show these practices are working. In California, water tables would have dropped hundreds of feet deeper without aquifer management. In parts of Arizona, they’re actually rising.

This doesn’t mean we can get cavalier about freshwater use. But it does show how human ingenuity can address critical environmental problems.

It may surprise you to know that the garbage that leaves your house will be preserved for centuries—in a landfill. More than a dump, landfills are an engineered storage system.

On the bottom, there’s a thick plastic membrane and a layer of compacted clay, to keep liquids from entering the groundwater.

Above that, the fill area is divided into cells for each day’s garbage. As trucks dump garbage into the cell, it’s compacted to become as small as possible.

At the end of the day, the cell is closed off with a layer of soil, and perhaps another layer of plastic, making it water- and airtight.

Most garbage won’t break down in this environment, though anaerobic bacteria will digest food and organic waste and produce methane, also known as natural gas, the same kind you burn in your stove.

Because it’s flammable, the methane has to be flared off. Or it can be collected and sold for industrial use. Or used to run electric generators at the landfill.

America leads the world, by a wide margin, in garbage production, with more than 1400 lbs per person per year. More than half of it ends up in landfills.

And 65 percent of that is packaging: cardboard, paper, plastic, bottles, and cans—nearly all of which could have been recycled.

On average, recycling costs about half as much as storing garbage in a landfill. So if you’d like to reduce your garbage footprint and your city’s municipal waste cost, recycling is the way to go.

The Earth has 3 million earthquakes a year, 8,000 every day. And some are caused by humans.

The crust of the Earth is composed of many tectonic plates, which are always moving.

As the plate boundaries collide, grind against, or pull apart from each other, the crust cracks, creating fault zones.

As stress builds up, the plate boundary faults can open or slide, causing natural earthquakes. The vast majority are too small to feel, but some can be major.

Sometimes human activities can trigger an earthquake, causing a fault to move earlier than it naturally would. In 2017, some British scientists decided to catalogue these.

They found that about half were due to extraction—of mining products, groundwater, or oil. Removal of material changes the stress, which can cause faults to move.

Another quarter were caused by loading the Earth’s surface where it was not loaded before, such as reservoirs held behind dams, which can add stress to faults.

The last quarter happen when fluids produced from the Earth are injected back into it, like in a disposal well, where wastewater from oil or gas production changes the pressure conditions, sometimes causing the fault to slip.

This last type gets a lot of attention these days, and we’re studying it extensively at the Bureau of Economic Geology, where I work.

Ever since humans have had large-scale industrial processes we’ve been interacting with Earth’s natural earthquake cycle … in ways we’re just now coming to understand.