Based on the IUGS Geologic Timescale Stratigraphy column.

One row per 10 million years. 8 rows/in = 58” scarf.

Yardage depends on gauge and width.

Scarf calls for 31 colors. Perfect for using up a lot of odds and ends, as most colors are used for only 1 to 4 rounds.

If one color is used for the Precambrian allow two balls or three balls for that.

Knit in round, size 2 or 3 circular needles and fingering yarn gives me 7 or 8 inches wide on 100 sts around. Cast on more stitches for a wider scarf, fewer for a narrow one.