In this study we investigate the light and heat-induced degradation of methylammonium lead iodide (MAPbI(3)) perovskite films in an inert atmosphere to exclude the effect of oxygen and humidity. Films aged under solar intensities started to degrade above 75 degrees C, while films in the dark degraded at 95 degrees C. To investigate the temperature-induced degradation mechanism, spectroscopic techniques such as Ultraviolet-Visible (UV-Vis) absorption spectroscopy, X-Ray Diffraction (XRD), Extended X-ray Absorption Fine Structure (EXAFS), and Fourier Transform Infrared (FT-IR) were used. Results show that the films aged under light at 75 degrees C degraded to a mixture of PbI2 and metallic Pb. In contrast, films aged thermally in the dark, or with light and oxygen, degraded to PbI2 only. MAPbI(3) solar cells were aged to show the effect of the metallic lead on the charge transfer mechanism.