Geological Timescale
What is the largest division of geological time?
An eon.
What is a fossil?
Preserved evidence of past life.
According to the principle of superposition, where are the oldest rocks found in an undisturbed sequence?
At the bottom.
Which organisms dominated Earth's oceans during much of the Paleozoic Era?
Marine organisms, including trilobites and other early arthropods, brachiopods, molluscs and early fish.
What is the term for the time required for half of a radioactive parent isotope to decay?
Half-life.
During which geological period did the Cambrian Explosion occur?
The Cambrian Period.
What is a mould fossil?
A negative impression left in sediment after an organism or part of an organism decays.
What principle states that geological processes occurring today also operated in the past?
Uniformitarianism.
Which organisms dominated terrestrial ecosystems during much of the Mesozoic Era?
Dinosaurs.
A fossilised footprint is discovered in a sedimentary rock. What type of fossil is it?
A trace fossil.
Which era contains the Triassic, Jurassic and Cretaceous periods?
The Mesozoic Era.
What is the difference between a mould and a cast?
A mould is a negative impression, while a cast is a positive replica formed when a mould is filled with sediment or minerals.
What type of dating places geological events in order from older to younger?
Relative dating.
What major evolutionary event marks the beginning of the Mesozoic Era?
The end-Permian mass extinction, followed by the recovery and diversification of new groups, including dinosaurs and other reptiles.
Scientists find the same index fossil in two geographically separated sedimentary rock layers. What can they infer?
The two rock layers can potentially be correlated and are likely to be of a similar relative age.
Which era is commonly known as the "Age of Dinosaurs"?
The Mesozoic Era.
What type of fossil provides evidence of an organism's activity or behaviour rather than its body?
A trace fossil.
What type of dating provides an estimated numerical age for a rock or geological event?
Absolute dating, commonly using radiometric dating.
What major event at the end of the Cretaceous Period led to the extinction of non-avian dinosaurs?
The Cretaceous–Paleogene (K–Pg) mass extinction.
A student says, "Radiometric dating and relative dating are the same because both determine the age of rocks." What is wrong with this statement?
Relative dating establishes the sequence of events or whether something is older or younger, while radiometric dating provides an estimated numerical age based on radioactive decay.
Put these geological intervals in the correct order from oldest to youngest: Mesozoic, Precambrian, Cenozoic, Paleozoic.
Precambrian → Paleozoic → Mesozoic → Cenozoic
Explain why rapid burial increases the likelihood of fossilisation.
Rapid burial reduces exposure to scavengers, physical disturbance and decomposition. This increases the chance that the remains will be preserved and eventually undergo processes such as mineralisation.
Explain why index fossils are useful for correlating rock layers.
Index fossils had a relatively short geological range, wide geographic distribution and were sufficiently abundant and recognisable. Finding the same index fossil in different rock layers can therefore indicate that the layers are approximately the same age.
Explain how mass extinction events can influence the subsequent evolution of life.
Mass extinctions remove many species and ecological roles, leaving vacant niches. Surviving organisms can then diversify and evolve into new species, resulting in major changes to ecosystems and the organisms that dominate them.
Explain why scientists combine fossils, superposition, index fossils and radiometric dating when reconstructing geological history.
Each method provides different information. Superposition establishes the relative order of undisturbed layers, index fossils allow correlation between layers, fossils provide evidence of past life and environmental change, and radiometric dating provides numerical ages. Combining these lines of evidence produces a more reliable reconstruction of geological history.