Comments on: The four types of planetary civilizations, explained by Michio Kaku https://lifeboat.com/blog/2023/10/the-four-types-of-planetary-civilizations-explained-by-michio-kaku Safeguarding Humanity Tue, 17 Oct 2023 15:32:06 +0000 hourly 1 https://wordpress.org/?v=6.6.2