The La Brea Tar Pits in Los Angeles, California, are a world-renowned paleontological site. This unique location preserves an extensive record of Ice Age life, offering a glimpse into ancient ecosystems. Over thousands of years, natural asphalt seeps have trapped countless organisms, creating a vast fossil collection. The ongoing scientific work at this urban site continues to reveal insights into prehistoric Southern California.
Understanding the Depths
The depths of the La Brea Tar Pits vary significantly across the site. Many visible surface seeps are only a few inches deep, appearing as shallow, sticky pools. However, these areas can connect to much deeper, buried asphalt deposits. The fossil-bearing layers extend far beneath the surface.
For instance, Pit 91, one of the most extensively studied excavations, reaches depths of approximately 15 to 20 feet (4.5 to 6.1 meters). Test coring in Pit 91 has reached a maximum depth of about 29 feet (8.8 meters) below the surface. Other pits are conical, extending downward for around 25 feet. Large-scale discoveries, such as those from Project 23, involved excavating fossil-rich deposits unearthed during construction, indicating significant buried asphalt layers.
How the Tar Pits Formed
The formation of the La Brea Tar Pits is a geological process. Crude oil, originating from underground reservoirs, has been seeping to the surface for thousands of years. This upward movement occurs through fissures in the Earth’s crust, allowing the petroleum to reach the ground.
Upon exposure to the surface, the lighter components of the crude oil evaporate. This leaves behind a thick, sticky residue known as asphalt, often colloquially referred to as “tar.” Rainwater and sediment accumulated on top of these asphalt seeps, forming deceptive pools of water. Unwary animals, drawn to these pools for a drink, became ensnared in the viscous asphalt, leading to their preservation.
What the Depths Reveal
The varying depths of the asphalt deposits hold scientific significance, providing a chronological record of past life. Different layers represent distinct time periods, allowing paleontologists to reconstruct ancient ecosystems and climate changes. Fossils retrieved from La Brea span approximately 40,000 to 8,000 years ago.
The sticky asphalt acts as an excellent preservative, encasing large animals and delicate materials. Researchers have uncovered a vast array of flora and fauna, including Ice Age mammals like saber-toothed cats, dire wolves, mammoths, and ground sloths. The pits have also yielded microfossils such as insects, plants, seeds, and pollen grains, offering a comprehensive picture of the ancient environment. The La Brea Tar Pits collection contains over 3.5 million specimens, and ongoing excavations like Project 23 continue to expand understanding of this unique prehistoric world.