http://www.snowballearth.org/week8.html
https://earthhow.com/great-oxygenation-event/
https://kids.kiddle.co/Snowball_Earth#:~:text=Snowball%20Earth%20or%20Icehouse%20Earth,in%20periods%20of%20the%20Proterozoic.
http://www.bbc.com/earth/story/20150112-did-snowball-earth-make-animals
https://astronomy.com/news/2019/04/the-story-of-snowball-earth
https://opentextbc.ca/geology/chapter/16-1-glacial-periods-in-earths-history/
https://www.newscientist.com/article/dn18949-the-history-of-ice-on-earth/
https://www.climate.gov/news-features/climate-qa/whats-coldest-earths-ever-been
