400 Million Years of Ferns

Ferns are all leaf, all the time—no slow preparation for the momentous flower, no seduction of the insect. At the tips of young fronds, fiddleheads unfurl, fronds lengthen, leaflets appear and widen behind the unfurling tip like the widening wake behind a boat. My store-bought Boston fern, tended for years with no expertise, bears dazzling fronds that arch up, out, and over—a fountain of green.

Ferns were among the earliest plants with roots to dig deep for water and vascular stalks and stems to transport it throughout the plant. They were the first to grow arrays of hundreds of leaves. This was almost 400 million years ago. Earlier plants had lived entirely in the water, with no need for deep roots. On land, before the ferns, the first mossy plants, lacking roots or stems, could grow no higher than a few inches. Vascular tissue—tubes that conduct fluids, minerals, and gasses—changed everything. Ferns reached the height of trees. And today vascular systems circulate the red blood through us all.

Ferns emerged late in the Devonian Period, which lasted from 419 to 359 million years ago. About 30 million years prior to the Devonian, the first of Earth’s five mass extinctions took place. The climate cooled, water froze, glaciers grew, the sea level fell, coastal and ocean habitats disappeared. As the earth warmed again, carpets of moss sprang up along lakes and streams and bony, heavy-jawed fish swam in the seas. Then ferns and other plants became the first forests.

Devonian ferns wikimedia


Toward the end of the Devonian, the second mass extinction took place. It came in three pulses. Ocean species, including the heavy-jawed fish, disappeared. But land plants, including the ferns, were mostly spared. In fact, one theory  (bbc.com/earth/story) holds that the roots of the ferns and other plants broke through rocks and released nutrients into the lakes, rivers, and oceans. The nutrients fed huge blooms of algae which later died and decayed, taking up the oxygen that had kept the fish alive. Meanwhile, again, the ferns thrived.

Ferns proliferated in part because of how they propagated. Here they were—and are—old fashioned. Instead of reproducing via miniaturized plants embodied in seeds, ferns spread through spores, single cells released from the underside of the fronds. When the spores settle on moist soil, they grow a tiny intermediate plant that will provide the fertile start for the new fern. Spore propagation seems a complicated two-step process, but the lightness of the single-celled spores let them disperse on the wind and germinate on distant, moist soil.

Some days I gawk at a plant whose distinctive family features date back 400 million years. No other plant or animal that I see every day goes back almost to the start of life on land. The ancestors invented leaves and roots but kept the old method of reproducing.  They survived four mass extinctions, as well as the flowering plants that burst on the planet 125 million years ago and dominated the plant kingdom. Ferns watched the dinosaurs come and go. Today they regale us with tales of ancient climates and their durable adaptations.


Note: Among the sources on ferns, Don Lubin’s “Introduction to Ferns” is especially readable and informative for the general reader.


Sink Or Float: The Ordeal By Water

Well-written history is often a reminder that although earlier people lived very differently than we do, their lives moved in many of the same spheres, with many of the same motives, as ours do. They managed sex, children, an economy; they punished cheaters, criminals, and often the vulnerable; they praised those who provided for them, or promised to. Their societies and circumstances were different, but they coped with their needs and with each other in recognizable ways.

Compelling examples of this appear in Michael Pye’s excellent The Edge of the World: A Cultural History of the North Sea and the Transformation of Europe (2015), about the rich complexities of northern Europe, often neglected, in what we think of as the Dark Ages, from about 500 to 1300.


In his chapter on the gradual emergence of law, Pye describes the “trial by ordeal” that preceded trial by judge or jury. We are familiar with one ghastly version of such justice. A suspect is bound and lowered into water. If they float, they are guilty and are executed. If they sink, they are innocent, and are pulled out. The ordeal was used for over a thousand years, early on for charges ranging from murder to land ownership claims but most famously for suspected witchery, sorcery, and heresy.

I’ve always thought of the ordeal by water as an outstandingly stupid method for establishing innocence or guilt. It’s absurdity seems highlighted by the Monty-Pythonesque craziness that the “fortunate” person who floated was found guilty and often executed.

But as Pye vividly explains, the appeal of the ordeal was that it claimed “the direct participation of God.” The water was holy water (or was supposed to be), and if the guilty party floated it was because the holiness of the water rejected the corrupt body. God’s participation seemed essential at a time when the state provided “no judge or jury [to] sort out facts and decide who is right… and wrong.” Written archives, files, paper trails, and law books were few.

In addition, “God’s verdict is unanswerable,” an irrefutable decision at a time when everyone in small communities knew each other’s business all too well. The command announced by priests at the ordeal’s opening ritual, “Judge not that ye be not judged,” was a stern reminder of the community’s fallibility. But the growth of trial by law book, judge, and jury, along with the withdrawal of the church’s approval of ordeals, gradually shifted the responsibility for verdicts from God’s hands to people’s.

For me, uncovering the thinking behind such alien customs, even the cruelest ones, helps me put people from the past into the stream of history that I too am swimming in, where we all make the best of our circumstances. This is a consolation of history; we are less alone in time and more at home on the planet when we understand a little of what prompted the strange behaviors of the past.


Where Water Came From

I always thought that water was part of the steamy mix of rocks and gasses that formed earth around 4.5 billion years ago. But these days scientists think that Earth was too hot and its gravity too weak to hold on to much water vapor. The belief now is that most of our water came in on comets and asteroids millions of years later. The current debate (Science News Magazine, May 16) is whether the vehicles were primarily comets, from far out in the solar system, or asteroids, from closer in, and what role Jupiter and Saturn played in pulling the water-laden rocks our way.

Water comes to earth (popsci.com)

Water comes to earth

The bombardment of extraterrestrial water is, in some ways, no surprise. All the atoms on earth have origins elsewhere. “We’re made of star-stuff,” as Carl Sagan put it. Water, though, is not an atom but a ready-to-use chemical compound. Of the key ingredients in physical life, it is the most visible, the one we are most conscious of. It makes up 60 % of us and flows into and out of us every day. And we can’t make more of it; there is only that original shipment.

To some people, this late and fortunate arrival of water may be one more sign of a master plan for life’s creation. That’s a reassuring notion. But from what I read, the arrival of so much water was essentially lucky. It could easily have happened on a much smaller scale or not at all. Thinking of our water as a lucky twist in the cosmic unfolding is cause for humility and appreciation.