The most common ancient use of petroleum tar seems to be in construction, the “slime” of the Babel story. Mixed with clay, sand, and straw, it was an easy, available, and durable mortar for binding together stones or bricks. Long before it fueled the human world, petroleum-based materials helped to build it.
A Lost World, Preserved
In 1769, a party of Spanish colonists trekked into what is now California’s Los Angeles County. According to Florence Josephine Seaman’s historical summary of the site, among the group was a Catholic priest, Father Juan Crespí, whose diaries record the findings of the expedition as they searched for the best place for their new settlement. As they traveled north, they passed what Crespí described as “extensive swamps of bitumen.” Local Indigenous people told him that they used the pitch, or la brea in Spanish, to seal their canoes.
Over the next century, the property acquired the title Rancho La Brea, and a new owner took possession of it. Henry Hancock began to harvest the material there after the Civil War, shipping it off to San Francisco and other ports for construction projects. As his crews dug deeper into the ground, they quickly discovered a different sort of treasure, a scientific gold mine that would redefine our knowledge of North America’s prehistoric life.
For about 50,000 years, the pit at Rancho La Brea had been capturing animals and other life, just as the Grand Canyon tar had caught Borell’s birds. But here, the excavated skeletons were often huge and unfamiliar. As experts arrived to study the finds, they discovered relatives of bison, sloths, and other large mammals that once walked California’s coasts and valleys. The pits were incredibly prolific, write William Akersten, Christopher Shaw, and George Jefferson. Between 1906 and 1915, workers and scientists unearthed roughly 2 million bones of large animals from La Brea. Immediately, a pattern started to emerge in the bones that both excited and confused the paleontologists. There were too many predators.
Dire wolves, saber-toothed cats, and other long-toothed hunters were everywhere in the La Brea pits, write Lillian Spencer, Blaire Van Valkenburgh, and John Harris. In ecosystems in the modern world, predators generally make up a relatively small percentage of both the individuals and biomass. Every predator needs many more prey to support it. A savanna with too many lions would quickly run out of gazelle. But here, the top predators dominated. More than half of all excavated skeletons belonged to carnivores.