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 ...

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.

But despite the extent of human-induced changes, last year the International Union of Geological Sciences (IUGS ... McCarthy ...