stratum

Everyday

1. (science) A stratum is one layer of rock or soil lying on top of another. tree →
2. A stratum is a layer of anything, such as the air or the sea. tree →
3. (formal) A stratum is a level or class of people in a society. tree →

In the lessons

In geography and science lessons strata are the layers you see in cliffs and canyons such as the Grand Canyon; lower strata are usually older, so they help scientists date fossils. In social studies it means a group at one level of wealth or power. Phrases: rock strata, social stratum, the upper strata.

Examples

• Each stratum of rock in the cliff was a different colour. tree →
• The fossil was found in a stratum of limestone. tree →
• The Grand Canyon shows hundreds of strata. tree →
• The lowest stratum of rock is usually the oldest. tree →
• A thin stratum of ash came from an ancient volcano. tree →
• (formal) The book is about people from every stratum of society. tree →
• Clouds can form in a stratum of cold air. tree →

Note

Plural strata (Latin), not «stratums». People often use «strata» as if it were singular; in careful writing say «one stratum, many strata». Related: stratosphere, stratus clouds.