While the La Brea Tar Pits are famous for saber-toothed cats and mammoths, the microscopic plant fossils trapped in the asphalt tell a different story. Pollen and seeds reveal 50,000 years of climate change in the Los Angeles basin.
A microscopic forest
The La Brea Tar Pits are an unparalleled collection of Ice Age fossils, but the story includes more than the immense skeletons of mammoths and saber-toothed cats. The same asphalt that trapped megafauna also preserved a vast and record of plant life. This collection of "microfossils" includes pollen, seeds, leaves, cones, and wood fragments from more than 150 identified species. These tiny remnants provide a high-resolution timeline of the Los Angeles basin's changing environment over the last 50,000 years.
Scientists extract these delicate fossils from the dense asphaltic matrix using a process. The matrix is washed with solvents, such as heated biodiesel or n-propyl bromide, which dissolve the sticky asphalt without destroying the organic plant material. Once cleaned, the material is sorted under microscopes, showing the ancient landscape grain by grain. The collection includes everything from juniper seeds and oak leaves to freshwater diatoms, which indicate the past presence of standing water on top of the seeps.
From redwoods to chaparral
The plant fossil record records a shift in the local climate. During the cooler, wetter periods of the Pleistocene epoch (the "Ice Age"), the plant assemblage resembled the coastal environment of modern-day Monterey, California, some 300 miles to the north. Pollen and macrofossils show evidence of mixed evergreen forests, including species like coast redwood (Sequoia sempervirens) and Coulter pines (Pinus coulteri), which are not found in the LA basin today.
As the climate warmed and dried heading into our current Holocene epoch, the ecosystem changed. The conifer woodlands receded and were replaced by the chaparral and coastal sage scrub plant communities that characterize Southern California today. One indicator of this change is the presence of two different juniper species. The Rocky Mountain juniper (Juniperus scopulorum), which prefers cooler conditions, alternated its presence with the more drought-tolerant California juniper (Juniperus californica). The eventual disappearance of the Rocky Mountain juniper from the area marks this long-term warming and drying trend. This detailed floral record, precisely dated using radiocarbon techniques, allows researchers to map the ecological response to major climate events over millennia.
💡Fun Facts
The most common plant microfossils found at La Brea are seeds from juniper trees.
Fossilized rodent droppings, some around 50,000 years old, have been recovered, providing direct evidence of what Ice Age animals were eating.
Scientists have found freshwater diatoms and ostracods (tiny crustaceans), indicating that pools of water formed on top of the asphalt seeps.
Asphalt is a natural substance, the result of crude oil seeping to the surface. Tar, by contrast, is a man-made product.
The museum is typically open daily from 9:30 AM to 5:00 PM. It is closed on the first Tuesday of each month (except June-August), Independence Day, Thanksgiving, Christmas, and New Year's Day. The outdoor park area is generally accessible from dawn until dusk.
Admission
General admission for adults is $18. Discounts are available for seniors and students. Los Angeles County residents receive free admission from 3-5 PM on weekdays.
Accessibility
The museum and surrounding paved pathways in Hancock Park are wheelchair accessible.