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.

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.
Canyon changes are tracked with pins.

Fact 1: when a hemisphere is tilted away from the sun , that hemisphere receives less direct sunlight. 
Fact 2: With less sunlight, the forest is cooler and wetter.
When a hemisphere tilts away from the sun, the forests there become cooler and wetter.

Fact 1: Evolution occurs by a process called natural selection. 
Fact 2: Birth and death are natural processes.

Evolution occurs through birth and death.