Fantastic Fossils
Preserved remains, traces, or evidence of ancient organisms stored in rock layers.
Fossil
The law stating that in undisturbed sedimentary rock layers, the oldest layers are at the bottom and the youngest are at the top.
Law of Superposition
Unlike relative dating, absolute dating provides this specific type of age for a rock or fossil.
Exact numerical age (in years)
The current geological Era we are living in, known as the "Age of Mammals.
Cenozoic Era
If a fault line runs straight through three layers of sedimentary rock, which is older: the rock layers or the fault line?
Rock Layers
Widely distributed fossils that lived for a short geological period, used to match rock layers of the same age.
Index Fossil
The principle stating that layers of sediment are originally deposited in flat, horizontal layers.
Original Horizontality
The fixed amount of time required for half of the radioactive parent atoms in a sample to decay.
Half-Life
The largest division/unit of time on the Geologic Time Scale.
Eon
Why are fossils almost exclusively found in sedimentary rocks rather than igneous or metamorphic rocks?
Heat and pressure in other rocks destroy/melt fossils
Footprints, burrows, and coprolites (fossilized dung) that show organism activity rather than body parts.
Trace Fossil
A gap in the geological rock record caused by erosion or non-deposition of rock layers.
Unconformity
What happens to the radioactive parent isotope over time as it decays during radiometric dating?
It turns into a stable daughter isotope
What major event usually marks the ending of one geological Era and the beginning of another on the time scale?
Mass Extinction
What is the term for a crack or break in Earth's crust along which movement or sliding has occurred?
Fault
Why are soft-bodied animals like jellyfish rarely found as fossils compared to animals with bones or shells?
Soft bodies decay too quickly before they can be buried and preserved.
According to the Law of Cross-Cutting Relationships, an igneous intrusion or fault line is always _____ than the rock layers it cuts through.
Younger
If a rock sample starts with 100 grams of a radioactive parent isotope, how many grams of the parent isotope are left after 2 half-lives?
25 grams
The time period covering the first 88% of Earth's history prior to the explosion of complex life.
Precambrian Time
A scientist who studies fossils and ancient life.
Paleontologist
What two environmental conditions are needed right after an organism dies to increase its chances of becoming a fossil?
Rapid burial by sediment and protection from oxygen/scavengers.
A piece or fragment of an older rock unit enclosed inside a younger rock layer.
Inclusion
If an element's half-life is 10,000 years and a sample has 25% of its original parent isotope left, how old is the sample?
20,000 years (2 half-lives)
Eras are divided into smaller time units called _____, which are then subdivided into epochs.
Periods
Which eon gets its name from the word "Hades" (hell) because Earth was a hot, chaotic ball of molten rock and lava?
Hadean Eon