The beginning and end of each chunk of time in the geologic time scale is determined by when some species appeared or disappeared from the fossil record. When many species went extinct around the same ...

“When you start naming geologic-time terms, you need to define ... We’re the first species that’s become a planet-scale influence and is aware of that reality. That’s what distinguishes ...

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.

Numerical ages estimate the date of a geological event and can sometimes reveal quite precisely when a fossil species existed in time. Third, magnetism in rocks can be used to estimate the age of ...

I like to use a meter stick and be very intentional with my spacing to model time as a scale. I also avoid using the far right ... of the Earth that is characteristic of a particular span of geologic ...