Which of the following is the best evidence of uniformitarianism?
a. In 20 years, a forest in Brazil is completely destroyed by the logging industry.

b. A 50 kilometer plain at the mouth of a river was formed at a rate of 1 millimeter per year.

c. An astronomer finds evidence that the solar system is 6,000 years old.

d. An underwater volcano's eruption forms a new island in about one month.