Dendrochronologists study tree rings to learn about past climates. Trees in temperate areas form one growth ring per year. Scientists can look at the rings and identify climate conditions during each year of the tree’s life. Scientists found long droughts in both the twelfth and thirteenth centuries. This is the same period when the Anasazi were leaving Chaco Canyon. Under normal conditions it was hard to support their villages in the harsh environment of northern New Mexico. When years of drought occurred, the densely populated Anasazi pueblos could no longer raise enough food. Other forces could have pushed the Anasazi away from Chaco as well.
There were about 60 million<span> people that were killed due to motor vehicle </span>collisions<span> and accidents. This number of deaths is around the same with the casualties recorded from the World War II. The motor vehicle collision is considered as leading cause of death among young adults.</span>
