While it's hard to say with absolute certainty who were the *very first* to populate land, the general consensus points to cyanobacteria and lichens as early pioneers.

Here's a breakdown:

* Cyanobacteria: These photosynthetic bacteria were likely among the first organisms to produce oxygen, a crucial step for the evolution of life on land. While they weren't multicellular, they formed mats and biofilms that could withstand harsh conditions. Some evidence suggests they existed on land as early as 3.5 billion years ago.

* Lichens: These organisms, formed by a symbiotic relationship between fungi and algae (or cyanobacteria), are remarkably resilient. They can survive in extreme environments and even break down rocks, contributing to the formation of soil.

While these organisms may have been the first to truly colonize land, there's also evidence suggesting that simple, single-celled organisms may have existed on land even earlier. However, their fossilization is less likely, making it difficult to confirm their presence.

It's important to note that the transition from water to land was a gradual process, and various organisms likely played a role in shaping the early terrestrial environment.