What was the likely cause of the mass extinction that killed the non-avian dinosaurs about 66 million years ago?
AA global flood
BA massive asteroid impact that caused climate disruption
CThe evolution of mammals that outcompeted them
DA disease that spread worldwide
About 66 million years ago, a large asteroid struck what is now the Yucatán Peninsula in Mexico. The impact caused massive fires, a 'nuclear winter' effect (dust blocked sunlight for months), and acid rain, devastating ecosystems worldwide. About 75% of all species went extinct, including all non-avian dinosaurs. Birds — the surviving dinosaur lineage — are the only dinosaurs that made it through.
Question 2 True / False
Once a species goes extinct, it can eventually re-evolve.
TTrue
FFalse
Answer: False
Extinction is permanent. While evolution can produce new species with similar features (through convergent evolution), it will never recreate the exact same species. The specific combination of genes, traits, and evolutionary history that defined that species is lost forever. This is why conservation — preventing extinction — is so important.
Question 3 Short Answer
Explain why a species that is well-adapted to its current environment might still go extinct.
Think about your answer, then reveal below.
Model answer: If the environment changes faster than the species can adapt through natural selection, the species may go extinct. For example, an animal perfectly adapted to a tropical forest will struggle if the forest is rapidly cut down or if the climate changes to become much colder. Adaptations are always relative to current conditions — when conditions change dramatically, former advantages may become irrelevant.
This is a critical insight: adaptation is not a permanent shield against extinction. Natural selection is slow (requiring many generations), and environmental changes — especially human-caused ones — can be extremely rapid. The mismatch between the speed of change and the speed of adaptation is what makes many modern species vulnerable.