The study of strata is called stratigraphy ... Each fossil species reflects a unique period of time in Earth's history. The principle of faunal succession states that different fossil species ...

The team says the strata where the drilling was done are known ... It is estimated that life began on earth about four billion years ago, but there is still debate about where and how it occurred.

of rock strata were carved away by ancient glaciers during the planet's Cryogenian ("Snowball Earth") period about 700 to 635 million years ago. "The fact that so many places are missing the ...