December 20th on the Cosmic Calendar: The first plants on land. Yes, up until now there have been no plants on land. Until now the land was just rock and sand, more like Mars than Earth today. Trilobites and the first fish aside — and we haven’t even gotten to dinosaurs yet — I find this somehow even more mind-blowing. Everything until now has been in the oceans. No trees — no green at all upon the land — no oxygen to speak of in the air, just rock and sand. Rock and sand. Rivers cutting their way through rock to the sea.
The first land plants likely evolved from algae living in shallow pools of water. That this water would evaporate was a problem for these algae. They had to evolve to be able to do without water for a while. Once they had done that, at some point water just from rain was enough and they were free to grow away from the pools. The colonization of the land by plants had begun!
Algae scum
Rebel scum
Sorry, I couldn’t resist (the dark side).
zorgor 
I like that you differentiated types of scum. Don’t forget money-grubbing scum.
Oh man! I forgot the money-grubbing scum!
Derp!