Prehistoric time line, geologic time scale, photos, facts, maps, and more from National Geographic. Humans have walked the Earth for 190,000 years, a mere blip in Earth's 4.5-billion-year history.

The geological time scale, established by scientists in the mid-19th century and agreed upon internationally, breaks down the eternity of our planet's history into more manageable units than years.

"But we're not nearly there now," Bennington said. “We’re talking geological time scale." That’s hundreds of thousands of years – and possibly much longer.

In 1913, before he even earned his doctoral degree, he proposed the first geological time scale, based on the fairly recently discovered phenomenon of radioactivity. Using his quantititive time ...

The deposit’s extraordinary scale has prompted a reassessment of how such formations evolve and persist through geological time. To provide clarity on the scale and importance of this discovery ...