ROCK OF AGES Plate tectonics may have started as early as 3.5 billion years ago on Earth. That recycling of Earth’s surface leads to the separation of light-colored continental crust (exposed here at Yosemite National Park’s Half Dome) from darker, denser oceanic crust.
IRMA INCOMING Hurricane Irma passed by Cuba on September 8, 2017, as a Category 4 storm (seen in this geocolor image captured by NOAA’s GOES-16 satellite) before making landfall in the Florida Keys on September 10, 2017.
BAD AIR U.S. pollution levels have come way down since the 1970s, but there’s still enough smog to raise the risk for cardiovascular deaths. Researchers are also drawing new connections between dirty air and metabolic and brain disorders.