The Harvard Museum of Natural History frequently presents free, public lectures in the Geological Lecture Hall, 24 Oxford Street, Cambridge.  They are live-streamed, and recordings of them are available here approximately three weeks later. Here are two upcoming STEM-related lectures:

• Adversity, Belonging, and Survival among Baboons: November 7, 6PM.
• Paleovirology: Ghosts and Gifts of Ancient Viruses: November 13, 6PM.