[2][3] He attended Amherst College as an undergraduate, where he received a bachelor's degree in geology and fine arts.

While in graduate school, in 1987, Johnson discovered an extinct species of linden leaf, which was named Tilia johnsoni in his honor.

[6] From 1991 to 2012, Johnson worked at the Denver Museum of Nature and Science, first as a lead scientist, then the chief curator and vice president of research and collections.

[7] In 2010, he led a nine-month excavation of thousands of Ice Age animal bones, including mammoths and mastodons, in Snowmass Village, Colorado.

[11] He is also the host of the two-hour Nova special Polar Extremes, first shown on February 5, 2020, which explores the history of the North and South Poles ranging from ice sheets to warm forests.