Conifers can be traced back 350 million years (to the Carboniferous). While swamps were dominated by horsetails and seed ferns, drier uplands were host to conifer trees. Early conifers were probably only 2-3 m (about 10 feet) in height. Leaves of these early conifers were needle-like but their cones were not as compact as modern cones. By the Permian, conifers had diversified into many forms, including large, woody trees much like modern conifers. At the end of the Permian, an enormous extinction event caused a major change in land ecosystems. Many of the primitive conifers went extinct, but survivors gradually spread during the Triassic until they became dominant forest trees. The early and middle Mesozoic (about 250-130 million years ago) became the age of conifers. Like modern forms, Mesozoic conifers were large, woody plants that made seeds. With the exception of one group that went extinct (the Cheirolepidiaceae), families of Mesozoic conifers are still on Earth today.

Plants on Earth began life in the water. The earliest plants were aquatic algae, living in the warm seas more than 500 million years ago. By the Silurian and possibly the latest Ordovician (as much as 440 million years ago), plant life on land had begun. While terrestrial plants had more access to sunlight, challenges included supporting their weight and distributing water throughout their tissues. During the Devonian explosion (55 million years, which is brief in geologic time), plants evolved from small, simple forms to a huge variety of larger, complex forms adapted to life on land. Club mosses, horsetails, ferns, and probably sphenopsids originated. The incredible seed, which safely packages the developing plant embryo, also evolved. Plants extended their reach underground with root systems, providing the anchor and water supply to support large trees. Although plants were to undergo many changes over time, by the end of the Devonian (the golden age of plant evolution), the groundwork had been laid for the terrestrial ecosystems of today.