The first Americans crossed into North America from Siberia via a land bridge that connected Asia to North America around 30,000 years ago during an ice age. As the ice age ended and temperatures warmed, sea levels rose and covered the land bridge. These early peoples adapted to various environments across North America, developing distinct cultural practices and ways of life. Native American cultures shared some common beliefs, including that nature has spirit, land cannot be owned, only use necessary resources, and trade was important.