Review Questions
- How old is the Earth?
- Why did early geologic time scales not include the number of years ago that events
happened? - Dinosaurs went extinct about 66 million years ago. Which period of geologic time was
the last in which dinosaurs lived? - Can scientists use the same principles they use to study Earth’s history to also study
the history of other planets? - SupposeyouarehikinginthemountainsofUtahandfindafossilofananimalthatlived
ontheoceanfloor. YoulearnthattherockthatholdsthefossilisfromtheMississippian
period. What was the environment like during the Mississippian in Utah? - Why are sedimentary rocks more useful than metamorphic or igneous rocks in estab-
lishing the relative ages of rock? - Which is likely to be more frequently found in rocks: fossils of very old sea creatures
or very old land creatures?
Vocabulary
absolute dating Methods used to determine how long ago something happened.
extinction When an organism completely dies out.
fossils The remains of past life, such as bones, shells, or other hard parts; may also include
evidence of past life such as footprints or leaf impressions.
geologic time scaleA timeline that illustrates Earth’s past.
relative dating methods UsedtodeterminetheorderofgeologiceventsinEarth’shistory.
Points to Consider
- How did life on Earth change from one period of geologic time to the next?
- When did life first appear on Earth?
- What conditions were necessary on Earth for living things to survive?