Martin thinks that analyses of 7,000-foot deep Antarctic ice cores provide support for his premise. He makes particular note of CO2 and iron concentrations found 18,000 and 160,000 years ago, about the time of earth's ice-ages. This information is given in the plots shown on the graph below.
(Note that scientists think that the iron found in the ice core came from dust that settled out of the atmosphere. The CO2 came from air trapped in bubbles in the ice.)