periods of time

[mengta]

Stratagraphic record is the layered arrangement created when mud, sand or silt is deposited over long periods of time.

is it correct to use "period of time" instead of "periodS of time"?
what's the difference?

thanks

[Casiopea]

. . . a layered arrangement . . . deposited over long periods of time.

'periods' works with 'layered'. The arrangement is made up of many layers or "strata", and each of those has its own time period: one layer represents one period of time; many layers represent many periods of time.

All the best,