algae are extremely cool and also murderous

there's a "killer algae" hypothesis to mass extinctions that argues (not without evidence) that algae are such a ridiculous terraforming agent that the impact of ecological shifts caused by an asteroid or massive eruption is multiplied many times over by the resultant changes to algae populations.

i mean, they caused the first mass extinction via terraforming. they shat oxygen in a world where oxygen was poisonous.