Bill Shear investigates how arthropods made the transition to living on land by looking at microfossils preserved along with fossil plants. He extracts tiny fossils by dissolving the rock that they are embedded in. He then puts together the fragments like a jigsaw puzzle and finds a spider was one of the first invaders. Further research showed that many different groups of arthropods invaded land around the same time. Shear then describes the ecosystem of the Devonian when this invasion occurred.