Normal AI Resource Spikes

I am playing PHC vs. Substrate AI, can crush him at will one level below normal.  On normal, I am clearly having map superiority when I am suddenly steam rolled by excessively large armies and quickly lose whether I focus on offense or defense.  Looking at the graphs, we are mostly even, then he has a series of huge Metal resource spikes on the chart, and one Radioactive resource spike.  Is there a resource drop feature I don't know about, or is normal getting a bonus to enable the sudden crush?