The Paleozoic era (the era of ancient life) began 570 million years ago. In the early periods of this era, a significant part of the land and the ozone screen was formed.
Further divergent evolution of the inhabitants of the seas took place.
The evolution of algae and invertebrates continued in the water. Marine invertebrates (molluscs, trilobites) have reached the greatest flowering.
The first vertebrates appeared – shell fish. They had an internal skeleton that gave them advantages in movement over invertebrates. Cartilaginous and bony fishes evolved from armored fishes, among which cross-finned fishes arose.
About 400 million years ago, living organisms came to land.
The first terrestrial plants were rhinophytes, in which integumentary, conductive, and mechanical tissues were formed.
Together with the plants, the first animals breathing atmospheric air – arachnids – came out onto the land.
Rhinophytes were replaced by ferns, horsetails and lyes, in which vegetative organs (roots, stems, leaves) were formed. Reproduction of spore plants depends on the availability of water.
Primitive amphibians descended from cross-finned fishes – stegocephaly – were the first among chordates to master the land. They lived in swampy places and could not move away from water bodies.
The humid and warm climate has led to the flourishing of ferns. At this time, the Earth was covered with forests of tree ferns, horsetails, and lyre.
Seed ferns have appeared.
Among animals, amphibians and arthropods prevailed. By the end of the Carboniferous period, the first reptiles and winged insects appeared.
The climate in many parts of the Earth has become dry and cold. Arboreal spores are dying out. The flowering of gymnosperms begins, for the reproduction of which water is not needed, and the embryo is in the seed and is provided with a supply of nutrients.
From amphibians originated truly terrestrial chordates – reptiles. The development of land provided them with the presence of a stratum corneum on the skin, internal fertilization and the development of the embryo in the egg. Animal-like reptiles appeared.