People and Pavement: A History (Part 1)

Illustration by Robert Bruce Horsfall (Frontispiece to A History of Land Mammals in the Western Hemisphere by William B. Scott, New York, MacMillan Publishing Company, 1913.

The Perfect Primordial Pitch

Asphalt. It’s a popular choice for driveways, roads, parking lots, racetracks, skate parks….  You get the gist. With 94% of paved roads in the United States covered with asphalt, many may wonder about the history of this resilient and popular material. And with good reason! The history of asphalt is thousands…no, millions of years long.

You may think we’re about to start babbling on about ancient Egyptians and Romans and other heralds of modern civilization. Hold your horses, we’ll get there. Before we do, though, how can one truly understand the history of this fascinating substance without first understanding what it is? For the first part of this in-depth history of asphalt, we’re taking you back—to the beginning of time.

Okay, maybe “the beginning of time” is a bit of an exaggeration. It’s estimated that the Athabasca oil sands in northeastern Alberta, Canada are around 110 million years old, though. So, you know…still pretty old. Obviously the asphalt we’re talking about here is the natural stuff—not the stuff that makes up our streets and driveways, today. That asphalt is actually shorthand for “asphalt concrete,” which has asphalt in it…plus some other stuff (we’ll get to that later). Clear as mud? Okay.

Naturally occurring asphalt—which geologists and countries other than the US tend to refer to as “bitumen”—is a sticky, black, highly viscous form of petroleum (classified as “pitch”) and has a consistency similar to that of cold molasses (but we wouldn’t recommend putting it in your cookies). Like other forms of petroleum, asphalt is formed from the remains of ancient, microscopic algae and other primeval organisms that have been buried under ocean and earth for a really, really long time. A very simplified equation might look like this: Heat (minimum 50°C) + Pressure (from all that ocean/earth) + Dead Stuff = Asphalt.

So this boiled, squished, corpse-riddled sludge, also known as asphalt, shows up in deposits and pits and asphalt lakes all around the world. You may have heard of the La Brea Tar Pits in Los Angeles? That “tar” is actually asphalt. Pitch Lake in Trinidad and Tobago, and Lake Bermudez in Venezuela are both asphalt lakes, and the oil and tar sands in Utah and Canada are filled to the brim with…you guessed it. Asphalt. And then there’s Alberta, Canada, which has the majority of the world’s reserves of natural bitumen, with deposits covering around 55,000 square miles—larger than the total area of England!

Until humans came along and found a use for the stuff, these deposits mostly just hung around and trapped unwitting wooly mammoths and saber-toothed tigers and the like. Once we figured out how to use tools and build things, though, it didn’t take long to discover inventive applications for this gluey gunk. But unfortunately, dear reader, we must leave you there. To learn more, tune in next month for People and Pavement Part 2, in which baby Moses makes an appearance and the ancient Romans find new ways improve upon their marching skills.

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