How forests were created

Forests are thought to have first appeared around 400 million years ago. Conversely one could say that until 400 million years ago, ours was largely a dead planet of dusty brown rock, soil and stones. It's hard to imagine isn't it? And where did the forests come from?

The appearance of the planet's first photosynthesizing organisms, known as cyanobacteria, can be traced back 2.7 billion years. Cyanobacteria living in sea shallows produced oxygen for the primeval planet, and over a very long period of time, the oxygen concentration in the atmosphere slowly grew.

Oxygen rising high into the air reacted with UV rays and was converted to ozone. As a result, around a billion years ago an ozone layer formed in the stratosphere. The ozone layer absorbed the sun's harmful UV rays, making the planet a safe place. The first organisms to take advantage of this were plants. Slowly they advanced to the water's edge, and around 500 million years ago in the Ordovician Period, plants such as lichens and ferns finally moved from sea onto land.

Three hundred and eighty million years ago in the Devonian Period, from among the plants that had advanced onto land came the world's first "tree", Archaeopteris. Archaeopteris is said to have had a growing trunk, and stand an impressive 20 meters in height. With no competition, it soon flourished, growing mainly near water in dense thickets. These were the world's first forests.

With forests come shade. The shade of trees shielded other life forms from harsh direct sunlight, and provided suitable moisture. In addition, the leaves falling from trees encouraged the activity of microorganisms, creating large volumes of organic material that supplied nutrients for hitherto barren soil, and transport down the rivers. Thus gradually the ground became a more comfortable habitat for life forms other than plants, and forests played a decisive role in the proliferation of life on land.

Frontier forest on Canada's west coast.
Frontier forest on Canada's west coast. The thick forest supports an amazing diversity of life forms. (Photo: Soichi Ueda)

The cycle of life
The cycle of life: from a fallen tree, a new tree starts to grow. (Photo: Soichi Ueda)

Then, around 300 million years ago, the gymnosperms or "naked seed" plants appeared, and between 150 million and 65 million years ago, in the golden age of the dinosaurs (from the Jurassic to the Cretaceous Period) sequoias (a member of the cedar family) and other conifers (gymnosperms) dominated. Angiosperms, "covered seed" plants that produce flowers and bear fruit, first appeared 130 million years ago. They devised a new way of propagating themselves: dispersing their seeds far and wide using insects, birds and mammals lured by their tasty nectar and fruit, in the process expanding the forest's ecological systems. Gymnosperms currently number around 800 species, but angiosperms have diversified to include 250,000 species.
Broadleaf trees (angiosperms) provided a new environment too for animals living in the forest. Because the branches of broadleaf trees unlike those of conifers spread out in a horizontal direction, trees became layered one on the other. This allowed animals to start moving considerable distances in the treetops without descending to the ground, where danger lurked. Our ancestors the primates, the most typical example being the orangutan, were originally forest-dwellers. Life in the spacious expanses of the treetops is said to have helped primates' eyes to evolve, and brains to develop.

Without the presence of forests, no life form, including ourselves, could have evolved on land. This means that even now, our continued survival depends on a symbiotic relationship with plants. Try pressing "8000 years ago" on the Earthrium globe to view the distribution of forests on earth before humans began to leave their mark on the planet. This is what our planet looked like after 400 million years of forest evolution, when forests and all other life on Earth including humans coexisted in a balanced manner.