Marginal world

Complex lifeforms either never evolved on this planet or went extinct sometime within the past couple million years. Perhaps the sun flared and knocked out the entire ecosystem, or maybe a slew of meteors struck, churning up enough dust that the sun was blotted out for several decades. Regardless, this world is ripe for colonization. Some terraforming will be required, however, if the world is to remain habitable over the long term.