Extinction and Appearance - Middle School Life Science
- Which evidence best indicates a species appeared (originated) in a rock sequence?
- Fossils first appear in a layer and are absent in all older layers. Shows the species didn't exist before this time.
- Identify the most likely conclusion: Fossil species X is in layers 3–7 only.
- Species X appeared by layer 3 and went extinct after layer 7. FAD at layer 3, LAD at layer 7 shows species' time range.
- What does last appearance datum (LAD) mean in the fossil record?
- Youngest known fossil occurrence of a species in rock layers. Marks the extinction or final local disappearance.
- What does first appearance datum (FAD) mean in the fossil record?
- Oldest known fossil occurrence of a species in rock layers. Marks when a species first evolved or migrated to an area.
- Which option best explains why a species might be absent from a layer without being extinct?
- It was not preserved or it lived elsewhere at that time. Fossilization is rare; absence doesn't always mean extinction.
- Identify the species with the latest last appearance: A LAD 9, B LAD 4, C LAD 6.
- Species A. Layer 9 is younger than layers 4 and 6, so A survived longest.
- Which term describes a species that lived for a short time but was widespread?
- Index fossil. Short-lived species make excellent time markers for dating rocks.
- Which evidence indicates two separated rock outcrops are the same relative age?
- They contain the same index fossil species. Index fossils correlate distant rock layers to the same time period.
- Choose the best inference: A new species appears immediately after a mass extinction layer.
- Survivors diversified and new species evolved after the event. Mass extinctions create ecological opportunities for rapid evolution.
- What is a key limitation that can make extinction look earlier than it truly was?
- Incomplete fossil record (preservation and sampling gaps). Not all organisms fossilize, creating false early extinctions.
- Which term describes a temporary absence of fossils even though the species survived?
- Fossil record gap (a hiatus in occurrences). Species survived but wasn't preserved or found in some layers.
- Which pattern best supports gradual evolution in the fossil record?
- A sequence of small trait changes across many successive layers. Slow, continuous change shows evolution happening gradually.
- Which pattern best supports punctuated equilibrium in the fossil record?
- Long stability, then abrupt change and a new species appearing. Rapid speciation after long stasis defines this evolutionary model.
- Which evidence best indicates a species went extinct in a stratigraphic sequence?
- Fossils stop above a layer and never reappear in younger layers. True extinction means no return in any later time period.
- What does it suggest if many marine fossils disappear at the same layer worldwide?
- A widespread extinction event, not a local habitat change. Global synchronous disappearance indicates mass extinction.
- Identify the best interpretation: Species A occurs in layers 1–4, never in 5–10.
- Species A likely went extinct after layer 4 (its LAD is in layer 4). LAD in layer 4 means no fossils found above that point.
- What is a mass extinction?
- A rapid extinction of many species in a short geologic time. Over 75% of species die out within a geologically brief period.
- Which evidence best indicates a species has gone extinct in the fossil record?
- Fossils stop above a certain layer but are present below it. Species existed in older times but disappeared from younger rocks.
- Identify the likely cause: Fossils of species Z are missing in one layer but present above and below.
- A preservation gap or unconformity, not definite extinction. Presence above and below rules out extinction at that time.
- What is the law of superposition used for when reading fossil layers?
- Lower layers are older; higher layers are younger. Sediments deposit sequentially, making bottom layers oldest.
- What is the best fossil-record evidence that a new species evolved from an earlier one?
- Transitional fossils showing intermediate traits in older-to-younger layers. Shows evolutionary connection between ancestor and descendant.
- What does a sudden disappearance of many species at the same layer suggest?
- A mass extinction event. Multiple species dying together indicates catastrophic environmental change.
- What is extinction in the fossil record?
- A species disappears and no younger fossils of it are found. No fossils of that species exist in rocks formed after that time.
- Identify the species with the earliest appearance: A FAD layer 5, B FAD layer 2, C FAD layer 7.
- Species B. Layer 2 is older than layers 5 and 7, so B appeared first.
- Identify the pattern that supports gradual evolution in a fossil lineage over time.
- Slow, continuous changes across successive layers. Fossils show incremental morphological changes through time.
- Which observation best indicates reworking (older fossils moved into younger rock) rather than true survival?
- Worn older fossils mixed into younger sediments with mismatched ages. Erosion can redeposit old fossils into younger sediments.
- Which conclusion is supported: Species C is in layers 2–3, absent 4–5, present 6–8?
- A gap in the record is likely; extinction is not supported. Reappearance after absence suggests preservation gap, not extinction.
- Which type of fossil is most useful for correlating rock layers by age?
- Index fossil. Their short time range precisely dates rock layers globally.
- Identify the conclusion: Species Y is found in older layers, but never above layer 10.
- Species Y went extinct at or after layer 10 (its LAD). Layer 10 represents the youngest occurrence before extinction.
- What is the most direct fossil evidence for a mass extinction event?
- Many unrelated species show LADs near the same boundary layer. Simultaneous extinctions indicate catastrophic environmental change.
- Identify the best interpretation: Species B is absent in layers 1–6 and present in 7–10.
- Species B likely appeared by layer 7 (its FAD is in layer 7). FAD in layer 7 marks the species' first occurrence.
- What is the simplest fossil-record definition of a species range?
- The interval from FAD to LAD in rock layers. Species existed between its first and last fossil occurrences.
- What does extinction mean when interpreting the fossil record of a species?
- Permanent disappearance of a species; no later fossils exist. Species is gone forever from Earth, not just locally.
- Which evidence best indicates a species has appeared in the fossil record?
- Fossils begin above a certain layer but are absent below it. Species didn't exist in older times, then evolved or migrated in.