SciShow
Viroids: Possibly the Smallest Pathogens on Earth
Potato spindle tuber disease wasn't a life-or-death situation, but it led to the discovery of viroids: infectious, replicating bits of RNA
SciShow
A Brief History of Life: Survival Is Hard
It turns out life may have gotten its start pretty early in Earth's history, and while the first couple billion years saw several important developments, the period was still dominated by very simple life forms. This is our first...