Rock Layers & Dating
What is the Law of Superposition?
(A: The oldest rock layers are at the bottom, and the youngest are at the top.)
What is an index fossil?
(A: A fossil from a species that lived for a short time and is found worldwide.)
What is the longest division of geologic time?
(A: Eon)
Which era is known as the Age of Dinosaurs?
(A: Mesozoic Era)
How do fossils help scientists understand the past?
(A: They show changes in Earth’s climate and life forms over time.)
What do scientists compare to determine the relative ages of rocks?
(A: Rock layers)
Name one reason why index fossils are useful to scientists.
(A: They help determine the age of rock layers.)
Put these time units in order from longest to shortest: Epoch, Era, Eon, Period.
(A: Eon → Era → Period → Epoch)
What era did the first fish, insects, and land plants appear?
(A: Paleozoic Era)
How do fossils help scientists match rock layers from different locations?
(A: If the same fossils appear in different places, the rock layers are likely the same age.)
What is the difference between relative dating and absolute dating?
(A: Relative dating compares rock layers, while absolute dating determines exact ages using radioactive elements.)
What are three characteristics of a good index fossil?
(A: Lived for a short time, found worldwide, and easy to recognize.)
What major events are used to divide Earth’s history into different time periods?
(A: Mass extinctions and climate changes.)
In which era did mammals take over and humans appear?
(A: Cenozoic Era)
Why are mammoth fossils important in understanding Earth’s climate?
(A: They show that parts of Earth were once much colder than today.)
Why do deeper rock layers contain older fossils?
(A: Older layers were buried first, so their fossils are older.)
What happens if an index fossil is found in two different rock layers far apart?
(A: The rock layers are likely the same age.)
What is the most recent era in Earth’s history?
(A: Cenozoic Era)
What time period makes up most of Earth’s history?
(A: Precambrian Time)
Why are fossils usually found in sedimentary rock rather than igneous rock?
(A: Sedimentary rocks form from layers of sediment where organisms can be buried and preserved, while igneous rocks are formed from molten lava.)
What could cause rock layers to appear out of order?
(A: Events like earthquakes, erosion, or folding of rock layers.)
What is an example of an index fossil from the Mesozoic Era?
(A: Ammonites)
Why don’t we know much about the Precambrian Time?
(A: Few fossils exist from that time because early life forms were microscopic.)
Name one mass extinction event and which era it ended.
(A: The asteroid impact that ended the Mesozoic Era and caused the extinction of dinosaurs.)
What type of fossils help scientists understand ancient animal behavior?
(A: Trace fossils, such as footprints and burrows.)