Combine the given two facts to write a concluding fact. Note that there should be some parts of the first and second facts that are not mentioned in this conclusion fact. Your combined fact should be the result of a chain between the two facts. Chains form when two facts connect together to produce a concluding fact. An example of a chain is: "pesticides cause pollution" (fact1) + "pollution can harm animals" (fact2) → "pesticides can harm animals" (conclusion fact). Parts of the concluding fact overlap with the first and the second fact. To construct such a  concluding fact, a useful way is to borrow the subject from one fact and the ending conclusions from another fact.
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Question: Fact 1: most canyons are formed by flowing rivers through erosion over long periods of time. 
Fact 2: Erosion was monitored by means of erosion pins.

Answer: Canyon changes are tracked with pins.


Question: Fact 1: measuring the hardness of minerals requires scratching those materials. 
Fact 2: Most gem stones are hard minerals.

Answer: You can measure the hardness of a gem stone by scratching it.


Question: Fact 1: heat can change the state of matter. 
Fact 2: Gas is one of the 3 states of matter.

Answer:
Heat can change something that has three states.