FOSSILS & RELATIVE DATING

GEOLOGIC TIME SCALEa series of time intervals that divides Earth’s history

• Each layer of rock represents specific interval of time

• Index fossils help determine specific period

• Time periods divided by specific events like mass extinctions

ROCKS TELL A STORY Rocks can tell where they were made and

when Sedimentary rocks can have fossils in them Rocks can tell when mass extinctions

happened

LAW OF SUPERPOSITIONFor undisturbed rocks, the oldest layer is on the bottom and the youngest is on top

Supai is oldest – WHY?

PALEONTOLOGYthe study of fossils remains of ancient life

Body fossils vs. trace fossils Body = remain of organism, like bones; Trace = evidence of organism, like footprints

Scientific dating Absolute dating (gives age in years)

uses radiometric / radioactive dating (isotopes) Relative dating (gives age before, after, during)

uses observation of rock layers

FOSSILS Traces and preserved remains of

ancient life found within rock layersFossils show:

Biodiversity How species have changed over time Correlation between rock layers from around the

world Relative ages to particular strata Evidence for the geological time scale

SCIENTIFIC DATINGAbsolute Dating: numerical

dating to give rocks an actual date or date range, in number of years

Relative Dating: compare how old something is in comparison to something else; used to put rocks and geological events in correct chronological order

HOW?Use sedimentary rocksUse fossilsStudy strata

INDEX FOSSIL Fossil that defines and identifies

geologic periods; often in only one layer of rock

Easily recognizable Exists over a short

geologic time range(found only in a few layers of rock)

Wide distribution(geographic rangeis world-wide)

Ex/ INDEX FOSSIL: AMMONITE

Ammonite fossils are found worldwide, existed for only a very

specific period of time

This means ammonites are found in very specific layers of rock;

Once we know the ammonites, then we can determine the age of any fossil found next an ammonite fossil.

What kind of rocks are these fossils in?

Which layer is oldest?

Which layer is youngest?

How do you know?

Quiz yourself!