Construct a scientific explanation based on evidence from rock strata for how the geologic time scale is used to organize Earth's 4.6-billion-year-old history.

  1. Space

    Astronomers spy fastest speeding star

    A few stars have been spotted departing our galaxy. The fastest of these might have been propelled by another exploding star, a new study finds.

  2. Fossils

    Dino double whammy

    Most scientists think an asteroid helped kill off the dinosaurs. But new calculations suggest that asteroid might have gotten some help from a long series of volcanic eruptions in what is now India.

  3. Earth

    When life exploded

    Life exploded in diversity during the Cambrian Period. Experts are exploring what could account for this sudden change 540 million years ago.

  4. Earth

    Meteorites likely wiped out Earth’s earliest life

    Enormous meteorites appear to have slammed into Earth several times early in its history. Each mega-smashup would have boiled off oceans and obliterated any bit of life.

  5. Planets

    Heavenly research

    Groundbreaking research in astronomy landed four high school seniors spots as finalists in the 2014 Intel Science Talent Search.

  6. Earth

    How Earth’s surface morphs

  7. Space

    The dark side of the universe

  8. Earth

    Deep drilling at sea

  9. Fossils

    Did dinosaurs do handstands?

  10. Space

    A galaxy far, far, far away