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The outline of a mastodon skeleton, found at a pre-Clovis site in Washington, indicating where a spear hit the animal. Image courtesy of the Center for the Study of First Americans, Texas A&M University

Sometime near the end of the Pleistocene, a band of people left northeastern Asia, crossed the Bering land bridge when the sea level was low, entered Alaska and became the first Americans. Since the 1930s, archaeologists have thought these people were members of the Clovis culture. First discovered in New Mexico in the 1930s, the Clovis culture is known for its distinct stone tools, primarily fluted projectile points. For decades, Clovis artifacts were the oldest known in the New World, dating to 13,000 years ago. But in recent years, researchers have found more and more evidence that people were living in North and South America before the Clovis.

The most recently confirmed evidence comes from Washington. During a dig conducted from 1977 to 1979, researcher uncovered a bone projectile point stuck in a mastodon rib. Since then, the age of the find has been debated, but last month in the journal Science, Michael Waters of Texas A&M University and colleagues announced a new radiocarbon date for the rib: 13,800 years ago, making it 800 years older than the oldest Clovis artifact. Other pre-Clovis evidence comes from a variety of locations across the New World. Here’s a brief tour of some of the most important sites:

Ayer Pond, Orcas Island, Washington: While digging in a wetland in 2003, workers discovered the bones of ancient bison, later radiocarbon-dated to about 13,800 years ago. Cuts on the bones and other signs of butchering indicate humans were in the area at that time. The researchers speculate that the hunters dismembered the bison on top of a frozen pond, leaving the carcass behind to fall to the pond’s bottom when the ice thawed.

Debra L. Friedkin site, Texas: An excavation at this site yielded 15,528 artifacts dating from 13,200 to 15,500 years ago. Named the Buttermilk Creek Complex, these small, lightweight tools—an indicator that the artifacts were designed to be carried around a lot—do not resemble Clovis tools, the researchers reported earlier this year in Science. But they may be the type of artifacts which later developed into Clovis tools.

Monte Verde, Chile: One of the first challenges to the Clovis theory came from southern Chile. In the 1970s, archaeologists discovered the remains of a campsite that dated to about 14,000 years ago, but the age was contested. In 2008, researchers obtained new radiocarbon dates from seaweed associated with stone tools at the site, placing humans in Chile as early as 14,200 years ago.

Paisley Caves, Oregon: So far, all of the pre-Clovis sites lack human bones; the case for a human presence is based solely on the discovery of artifacts and butchered bones. The Paisley Caves in Oregon, however, contain a type of human remains: fossilized poop, or coprolites if you want to be more scientific (and polite). Fourteen coprolites at the caves resembled human coprolites based on size, shape and other physical features. DNA from the samples confirmed their human origin. Radiocarbon dating indicates people left the specimens behind between 14,000 and 14,270 years ago. Canid DNA in the coprolites suggests early Americans may have eaten dogs, wolves or foxes; alternatively, such animals later came by and urinated on the dung.

Meadowcroft Rockshelter, Pennsylvania: Just an hour’s drive from Pittsburgh, Meadowcroft may be the oldest site of human habitation in the New World. The first artifacts were found in the 1950s, and subsequent excavations unearthed small stone blades, flakes and a projectile point that date to as many as 15,200 years ago. Some researchers think humans first called the rockshelter home even earlier, about 16,000 years ago. To imagine what life was like for America’s earliest immigrants, you can take a tour of Meadowcroft, which is open to the public May through October.