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Dating rocks

Dating rocks

Dating rocks

  • Exhibition Text

    • The immensity of time
      In order to understand geological processes, we need to envision time periods far greater than the hourly, daily, and yearly progression that dominates our everyday lives. Major changes in the continents, oceans, atmosphere, and biosphere occur over millions of years, and usually cannot be detected from one year to the next. But the Earth’s rocks provide clues that allow scientists to piece together the planet’s 4.5-billion-year history. 

      Fossils record relative time
      Prior to the 20th century, geologists could only determine the relative ages of rocks — whether one was younger or older than another. Working in the Bath district of western England, William Smith (1769–1834), an engineer and surveyor, saw that rock layers could be dated.

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In This Section



This Middle Cambrian trilobite fossil (Paradoxides tessini) was found in a 540-million-year-old carbonate-rich shale.



Herbertella insculpta is a brachiopod from the Ordovician period (438 to 505 million years ago). 

Telling Time Precisely

Telling time precisely

The discovery of radioactivity in 1896 made it possible to determine the precise ages of rocks.

Fossil Fish

Fossil fish

Knightia is an extinct freshwater herring from Eocene freshwater herring from the Eocene period (about 40-55 million years ago).

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