- An animal is a kind of organism
- A horse is a kind of animal
- Hence, a horse is a kind of organism

- A horse is a kind of organism
- If fossils of an organism change depending on the level in which they were found then that species of organism changed over time
- So, if fossils of horses change depending on the level in which they were found, then the horses has changed over time

- The fossils of horse has shorter bones in lower levels and the fossils of horse has longer bones in the upper level
- Younger layer of rocks are on top of the older layer of rocks according to superposition
- Hence, the younger fossils of horse has longer bones than the older fossils of horse

- If fossils of horses change depending on the level in which they were found, then the horses has changed over time
- The younger fossils of horse has longer bones than the older fossils of horse
- Therefore, horse species have changed from smaller to larger over time

So, horse species have changed from smaller to larger over time
[Question]A geologist found fossils of horse bones in different rock layers of a canyon. The fossils in the lower levels show shorter bones than those in the upper-level fossils. Which conclusion is based on the geologist's observations?
[Context]- The fossils of horse has shorter bones in lower levels and the fossils of horse has longer bones in the upper level 
- An animal is a kind of organism 
- Younger layer of rocks are on top of the older layer of rocks according to superposition 
- A horse is a kind of animal 
- If fossils of an organism change depending on the level in which they were found then that species of organism changed over time