Question

index fossils
across

1. species that became index fossils existed for a relatively short period of geologic time and became ___ fairly quickly.
2. the organisms that became index fossils were found in very large quantities, meaning these organisms were ___ at one time.
3. index fossils are ___ and easily recognizable.
4. index fossils are globally ___.
5. ___ found in sea water falls to the oceans floor, covering dead organisms.
6. a type of rock made of sediments that become cemented together
7. very small fossils that are only visible with a microscope

down

1. organisms that became index fossils were ___, holding up well over a very long period of time
2. ___ fossils older than 200 million years old can be found on land due to plate tectonics
3. most rock that contains fossils were formed in the ___.
4. these carried the floating eggs and larva of many marine organisms all over the globe
5. fossils that help determine the age of fossils and rock found in the same sedimentary layer.

Explanation:

Each answer matches the definition provided for the crossword, based on paleontology/geology concepts related to index fossils:

1. Down 1: Index fossil organisms need to be durable to fossilize well over time.
2. Down 2: Marine fossils can end up on land due to plate tectonics shifting ocean floors upward.
3. Down 3: Most fossil-bearing rocks form in oceans, where sediment accumulates to bury organisms.
4. Down 4: Ocean currents carry marine larvae/eggs globally, helping index fossils spread widely.
5. Down 6: Index fossils are defined by their ability to date associated rocks/fossils.
6. Across 5: Index fossil species spread widely (became abundant) quickly over a short geologic time.
7. Across 7: Index fossils come from organisms that were widespread (numerous across large areas).
8. Across 8: Index fossils must be distinct and easy to identify.
9. Across 9: Index fossils are found across the entire globe (widespread geographically).
10. Across 10: Sediment in seawater falls to the ocean floor to cover dead organisms.
11. Across 11: Sedimentary rock forms from cemented sediments, where fossils are typically found.
12. Across 12: Microfossils are tiny fossils only visible with a microscope.

Answer:

Across

1. ABUNDANT
2. WIDESPREAD
3. DISTINCT
4. DISTRIBUTED
5. SEDIMENT
6. SEDIMENTARY
7. MICROFOSSILS

Down

1. DURABLE
2. MARINE
3. OCEAN
4. CURRENTS
5. INDEX