FERNS ARE IMPORTANT
Nowadays, ferns and their club-moss and horsetail relatives comprise about 3% of the vascular plant species in the U.S. and Canada, and even less of the biomass. They are pretty little plants growing mostly in damper areas, without much commercial utility. We might even get along without them. For a time.
When earth solidified around four and a half billion years ago, the atmosphere had lots of carbon dioxide and sulphur, and almost no oxygen. After a couple of billion years, life had developed in the oceans, and cyanobacteria started converting CO2 into O2. Nearly all that oxygen combined with metals in the ocean and fell to the bottom to form the red rocks and clays we see today. That process was completed by about 600 million years ago, and then the oxygen content of the atmosphere started to climb, and life exploded. Cell walls. Multicellular organisms. Specialization. Algae gave rise to mosses with a waterproof coat, and spores that enabled propagation over larger spans of space and time.
Plants first developed a circulatory system over 400 million years ago. Horsetails, club-mosses, Isoetes, and ferns could grow more than four inches tall and still get water to their tops, and then grew up to 120 feet. They could send their roots and rhizomes deep beneath the surface, to reach the water table and to stabilize the taller plant; they could send oxygen down to the roots. This freed them from the narrow edges of lakes and swamps, and invasion of the land masses began. They produced biomass that mixed with the rock dust and sand to create soil.
Ferns invented leaves, and photosynthesis increased enormously, clearing volcanic CO2 from the air and producing all of our coal deposits from their biomass. During the Carbon Age, 360 - 300 million years ago, oxygen levels grew to 35%, a figure not seen before nor since. Huge insects flew through the new forests, and larger animals began to crawl up onto the land. Rivers were lined with large rooted plants that stabilized their courses, so they no longer meandered over the whole valley washing away any progress. Fields and forests could develop. All this happened more than twice as long ago as when the first flowering plants evolved.
The earth has seen five mass extinctions in which more than 50% of all species have died out. Humans are causing the sixth one now, in part by digging up the carbon that ferns sequestered and putting CO2 back into the atmosphere. The last two extinction events were followed by Fern Spikes. When a meteor or whatever crashed near the Yucatan, the shock wave, fires, and months of darkness and cold killed off most species, including dinosaurs. In North America, pollen disappeared for a while as all spermatophyte plants died out. But spores of ferns and their relatives soon filled the gap, and managed to recreate a liveable environment, regenerate the soil, clear the air, and welcome other life forms back again.
Ferns did not invent just leaves and coal. They and their relatives also created soil, air as we know it, forests, fields, and rivers. If our planet undergoes another catastrophe of similar scale, ferns will again be needed to reboot life on earth.