What are measured in eras and periods?

Answer 1

Eras are great lengths of time but periods are the small amounts of time in eras.

Answer 2

Super-Eons, Eons, Eras, Periods, Epochs and Ages are all units of geological time.

Super-Eons are divided into Eons, Eons in Eras, Eras into Epochs and Epochs into Ages.

An example is

The Precambrian Super-Eon (4,500 - 542 Ma) is divided into the

Hadean Eon (4,500 - 3,800 Ma),

Archean Eon (3,800 - 2,500 Ma) &

Proterozoic Eon (2,500 - 542 Ma).

The Proterozoic Eon (2,500 - 542 Ma) is divided into the

Paleoproterozic Era (2,500 - 1,600 Ma),

Mesoproterozic Era (1,600 - 1,000 Ma) &

Neoproterozic Era (1,000 - 542 Ma).

The Neoproterozic Era (1,000 - 542 Ma) is divided into the

Tonian Period(1,000 - 850 Ma),

Cryogenian Period (850 - 630 Ma) &

Ediacaran Period (630 - 542 Ma).

And so on.

Answer 3

Eras and periods both appear at the start of the Cambrian period.

Answer 4

Geologic time scale