Chapter 1 section 1 reteaching activity peopling the americas

The first Americans arrived as early as 22,000 years ago. It is believed that they crossed a frozen land bridge between Asia and Alaska now called Beringia, and into North America. Some groups may have also edged down the Mississippi River in boats. Evidence suggests that these first Americans were big-game hunters and that their most rewarding prey was the woolly mammoth, which provided them with many of life's essentials. Between 10,000 and 5,000 years ago, people began to experiment with fire in what is now central Mexico. Archeologists believe that corn was the first plant that ancient Americans developed for humans use. The growth of agriculture allowed people to settle down in one place and build communities. This, in turn, led eventually to the development of civilizations.

2018 means 2018 ce or common era

there have been other eras too including bce, which included way more years.

to act quickly in times of danger to the united states

because you have to act quickly if you want to live/survive.