陸上への進出

Over three and a half billion years ago, lifeforms could survive only in aquatic environments. Later, some prokaryotes, such as cyanobacteria, began fixing carbon dioxide to produce sugars through photosynthesis.

These photosynthetic organisms released oxygen, and it accumulated in the atmosphere.

Evidence suggests that single-celled photosynthetic microbes colonized moist terrestrial surfaces more than two billion years ago.

While land environments provided abundant sunlight and carbon dioxide, two crucial components for photosynthesis, they also presented challenges such as desiccation, UV exposure, and lack of structural support.

Multicellular plants and fungi gradually evolved the ability to live on land around 470 million years ago.

This transition required several adaptations. Some cells formed shoots that capture light, while others formed root-like structures that anchor the plant and absorb water and nutrients.

Other structural changes also helped plants survive on land. For example, a waxy cuticle limited evaporation.

Cell walls provided structural support, while vascular tissue helped move water through larger plants.

Around 450 million years ago, arthropods were the first animals to evolve the ability to live on land.

These organisms had external skeletons and belonged to the group that includes modern insects, arachnids, and crustaceans.

Early tetrapods evolved around 380 million years ago. Their lobe-finned fish ancestors had features like lungs and stronger limb bones that helped them move from water onto land. They later diversified into amphibians, reptiles, birds, and mammals.

Plants that had already colonized land formed the base of early terrestrial food webs, supporting both arthropods and tetrapods. Through this gradual process, plants, fungi, and animals colonized Earth’s landmasses and eventually evolved into the diverse species that exist today.