Most often when we think about exercise we think aerobic. That is in part because of the high energy classes available at most gyms. Aerobic exercise is not confined to those classes, however. For most people, low to moderate exercise or exertion is generally aerobic.
The biggest iron mine. The worlds biggest open pit iron mine can be found near Hibbing, Minnesota. At its maximum, the area covered by the Hull Rust open pit mine is five miles (8km) long, 2 miles (3,2km) wide and 535 feet (180m) deep. It looks like a man-made Grand Canyon of over 2,000 acres (8,1kmÂ²).
Today, the mine is one of the largest gold- and copper-extraction operations in the world. The open pit is 2.5 miles wide, and there is extensive underground mining in the area as well. Glaciers are also visible in the image. This photograph was taken June 25, 2005, by astronauts on the International Space Station. Image: NASA