Yes, ERAS is a Scrabble word!

Letter values in Scrabble US: E 1, R 1, A 1, S 1.

Is it a valid word?

ERAS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a period marked by distinctive character or reckoned from a fixed point or event
a major division of geological time; an era is usually divided into two or more periods
(baseball) a measure of a pitcher's effectiveness; calculated as the average number of earned runs allowed by the pitcher for every nine innings pitched

Also: geological era, earned run average.