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Hank: More than 4500 years ago, Finnish pottery makers discovered a stone made of thin fibers that mixed really well with the clay they used to make pots. This peculiar stone was so strong and yet flexible that they could use it to make their pots thinner and bigger than ever. Plus, it was surprisingly resistant to heat so the pots could hold things like hot metal. It seemed like something of a miracle stone and eventually the ancient Greeks and Romans and Egyptians all started using it, too. That rock was what we now call asbestos and eventually we found out that it was too good to be true and stopped using it so much. That took a pretty long time.

The word asbestos actually refers to six different minerals that all have the same habit, or way their crystals grow. They're called asbestiform, which just means that they grow in long, thin, flexible fibers. That flexibility, plus their strength and resistance to damage by heat and harsh chemicals made these minerals incredibly useful in industry.

The problem, of course, is that inhaling asbestos fibers can be dangerous because to your lungs those flexible fibers are more like sharp little knives. You can probably imagine what happens if you breathe them in, they get stuck in the mucous lining of your lungs which can make it difficult to breathe. Inhale too many of the shards at one time, and they can cause diseases like asbestosis, or scarring of the lungs, and mesothelioma, a type of lung cancer.

The forms of asbestos with the highest health risks are part of a group of rocks called amphiboles, and what makes them cause more health issues than others comes down to four of their chemical and structural properties. First, amphibole fivers are smaller, so they can travel deeper into the lungs, they're also sharper, so they can pierce your lungs more easily causing inflammation or creating scar tissue. Plus, they're hydrophobic or water-avoiding which can keep them from dissolving in mucous. If they dissolved, they could get coughed up and get out of your system. Finally, they contain iron which can react with oxygen in your lungs and damage the DNA in your lung cells. The damaged DNA can then make the cells divide too quickly leading to a tumor, so they may be more carcinogenic or cancer-forming as well.

So how did asbestos go from being the miracle rock of ancient potters to being the scourge of modern industry? Well even as far back as the Roman Empire some 2000 years ago, historians wrote about slaves getting what they called a "sickness of the lungs" after working in asbestos mines, and when the first commercial asbestos mines opened in Quebec in 1879, asbestos related health issues started showing up in medical journals and case reports.

One of the first well-studied deaths was in 1924 in the UK. Nellie Kershaw, who'd been spinning asbestos into yarn since she was 13, died at the age of 33 from asbestosis. When Parliament heard about the case, they asked a doctor known as ERA Merewether to investigate the health of asbestos workers.

For two years, he studied 374 workers at an asbestos textile factory. He found that inhaling asbestos fibers caused scarring in the lungs, and 17 out of 20 workers who had been there for more than 20 years ended up with asbestosis. Merewether presented his paper to Parliament in 1930 and the UK started requiring ventilation in asbestos factories a year later. But it wasn't until 2003 that asbestos was banned throughout the European Union. The asbestos industry in the United States is a whole other story.

Asbestos was used a whole lot during World War II, since it was cheap, strong, and resistant to fire and chemicals. Naval warships used asbestos insulation and buildings were constructed with asbestos floor tiles and shingles, cements, and insulation for pipes. Production of asbestos in the US finally started to slow down in 1979 when nine asbestos manufacturers filed a lawsuit against the federal government.

In 1975, they paid $69000 to an asbestos worker who developed asbestosis, and the manufacturers wanted to be reimbursed. But the government wasn't having any of that, instead, they proved that the companies knew about and had been hiding asbestos related health information for decades. The case got a lot of media attention and people started to try to fix the problem by removing asbestos from buildings, but the US still hasn't entirely banned the use of asbestos.

Even so, asbestos won't cause health issues for most people. Most of the fibers are so tightly bound into another material that they won't escape into the air unless you're trying to remove the asbestos. Plus, every year we, and everyone else on Earth, breathe about a million fibers just from the natural erosion of asbestos-containing rocks. So unless you're an asbestos worker who spent a lot of years without a ventilation mask, or you're an ancient Finnish potter, you don't have to worry about getting an asbestos-related illness anymore.

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