As you read this passage, think about how to describe its tone. New research identifies cracks over the moon's crust that may have been created by the cooling and shrinking over the past billion or so years. Scientists have discovered landforms littered across the moon's surface called lobate scarps that have apparently resulted from the moon's shrinking very slowly. These scarps were found all over the moon and appear to be minimally weathered, indicating that the geologic events that created them were fairly recent. This theory contradicts the claim that the moon is completely devoid of geologic activity.

What word best describes the tone of the passage?
personal
formal
casual
simple