The Sticky Trap That Kept a Zoo

The story

In the middle of Los Angeles, one of the busiest cities on Earth, sticky black goo seeps up from deep underground, as it has for tens of thousands of years. In a city park it gathers in fenced pits and pools, the biggest an old mining pit now filled with water, burping lazy bubbles from the asphalt below. The goo is natural asphalt, and people call this place the La Brea Tar Pits.

And from that goo, scientists have dug one of the greatest treasure chests of Ice Age remains in the whole world: mammoths with sweeping tusks, lions bigger than today's lions, giant ground sloths heavier than a horse, fierce wolves, and the famous sabre-toothed cats with teeth like curved daggers. Millions of specimens, most of them kept in the museum right there in the park. How did the remains of a whole vanished zoo end up in puddles of black glue?

Picture it long, long ago, before any city, when this was open ground. The sticky seeps were there even then, lurking. In warm weather the asphalt turned soft and extra gluey, and here was the sneaky part: wind blew dust and leaves across the surface, and rain sometimes pooled on top, so a deadly sticky patch could look like harmless ground, or like an innocent puddle for drinking. Along comes a huge, heavy animal, a mammoth perhaps, plodding across the plain. A few steps onto the wrong patch, and its great feet sink and STICK. The goo does not gulp animals down like quicksand in a cartoon. It simply grips, patiently, and will not let go.

Then, scientists believe, the trap often played its cruellest trick, and a surprising clue backs them up. A trapped animal is exactly the kind of easy meal that draws hunters and scavengers, by sight, by smell, perhaps by its cries. Wolves trot in. Sabre-toothed cats slink close. And the sticky ground catches THEM too. The clue is in the counting: the pits hold far more hunters than plant-eaters, exactly what you would expect if each trapped animal became bait for the next. Dire wolves, big Ice Age hunters of the dog family, are the most common large mammal in the whole collection, thousands of them, guests at a dinner that never let anyone leave.

What the goo caught, the goo KEPT. Sealed away from air and weather, soaked in preserving asphalt, the bones lasted while whole ages of the world rolled by. People began digging in earnest about a hundred years ago, lifting out enormous numbers of stained brown bones, and excavation has continued off and on ever since. Scientists still work in the park today, uncovering and studying new finds, a window into the Ice Age one bus ride from downtown.

So the tar pits turned out to be something no one intended: a library. A sticky, patient library that recorded which creatures roamed this corner of ancient California, and saved the pages for us.

Remember that the ground under every city is keeping some kind of story, and sometimes, when we dig carefully, the ground tells it.