Other forms: uniformitarians
A uniformitarian is someone who agrees with the idea that the processes affecting Earth's geology have always acted in essentially the same way they do today. All modern-day scientists are uniformitarians.
Before the mid-1800s, most scientists were catastrophists, believing that Earth's natural formations developed quickly from a series of catastrophic events and that mass extinctions were followed by brand new life forms. The modern science of geology grew out of uniformitarians realizing that the processes and natural laws observed today have existed throughout history. They saw that uniform changes over time account for all of the planet's remarkable features, from canyons and river valleys to mountains and islands.