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.


Survivors and the Terminator

The story of evolution recounts the ways that plants and animals have changed over time as small bodily variations have improved their odds for survival. But what about those species that fitted so successfully early on into stable environments that they have altered little or not at all? Are any such ancient species (besides the microbes) still around today?

Yes. In Survivors: The Animals and Plants that Time Has Left Behind (2011), Richard Fortey tracks down present-day plants and creatures that look much like their fossilized ancestors. Oddly, their stories of sameness impress me with as strong a sense of evolution’s power as stories of modification; natural selection goes with what works, whether it’s new or old.

Horseshoe crabs, after half a billion years, still crowd the beach. (delaware-surf-fishing.com)

Horseshoe crabs, after half a billion years, still crowd the beach.

In the opening chapter, Fortey is on a beach in Delaware on the night of the annual horseshoe crab orgy, when thousands of male horseshoe crabs come ashore to clamber on top of the females. Horseshoe crabs have  been scrambling up beaches for 500 million years.

In the darkness along Delaware Bay the scratching percussion of the crabs provides an unmusical accompaniment on an imaginary journey backwards in time: to an era well before mammals and flowering plants; a time before the acme of giant reptiles, long before Tyrannosaurus; backwards again through an extinction event 250,000,000 years ago that wiped nine-tenths of life from the earth; and then back still further, before a time of lush coal forests to a stage in the earth’s history when the land was stark and life was cradled in the sea.

firmoss (newfs.s3.amazonaws.com)

Four hundred mya, plants like this Norwegian Huperzia moved from the water to land and were among the first to acquire the crucial, stiffened water-conducting tubes–today we know them as stalks–that enabled them to stand upright and compete for light.

In the other chapters, Fortey describes the velvet worm in New Zealand, the lovely Norwegian fir moss, the not-so-lovely lungfish. The photo captions here mention their keys to long-running adaptive success.

It helps that their environments have changed very little. “Survival is about endurance of habitat.” One habitat that endures is the tidal flat, where the shallow sea meets the muddy shore. Organisms here can burrow, find oxygen in the water and air, find food through filtering or scavenging. Here are horseshoe crabs, snails, small fish, many plants. “This habitat does seem like a good place to be for an organism with conservative tendencies. If its own place survives, then so will the beast. It is the right place to weather mass extinctions that affect many other environments more severely.…Stick-in-the-muds last longest.”

As for the durable species themselves, a few characteristics recur. “Many…seem to have long life spans.” Horseshoe crabs take a decade to mature. And some enduring animals invest more resources in fewer progeny by producing “relatively large eggs or few offspring.” But there are no fool-proof formulae. “[T]he luck for old timers will eventually run out. It always does.”

lungfish (media-web.britannica.com)

In Australia, Fortey finds the lungfish that dates back 400 mya, “the great survivor among the vertebrates, the animals with backbones.” With lungs, these sea creatures, in transitioning to the land, can gulp air whenever the river runs low on oxygen.

What about humans? When will our time run out? Fortey doesn’t make guesses, but he has a hard label for us.

[Early man] may have hunted edible mammals and birds to the point of obliteration even in his earliest days; he was the first species that deserves to be called the Terminator….The extinction event that is happening right now is the first one in history that is the responsibility of a single species. There’s no meteorite this time, no exceptional volcanic eruptions, no ‘snowball earth,’ just us, prospering at the expense of other species.

He is confident about the survival of only one kind of organism. “I am not worried about the survival of bacteria. They will be there to rot down the last bodies of the last humans, and then the wheel of life will have turned full circle.” So ends the book.


Global Warming and the Cold War

When I was 14, my father brought me down to the furnace area in our basement to show me the water, food, and other supplies he had stockpiled to the ceiling. He gave me memory tips for finding my way to his hometown in North Dakota and the drug store where “they will take you in” if the East coast was bombed. I remember watching Kennedy on television in 1962 during the Cuban missile crisis the first year I was at college and thinking I might never get home. Into the 1980s, the nightmare was that if the shock waves and the fallout didn’t get us, the global chill from the atomic dust would.

The melting (scitechdaily.com)

The melting Arctic (scitechdaily.com)

Today the grand anxiety is of global warming instead of nuclear winter. Here in New Jersey, though, the concern is subdued. The state energy plan is all about natural gas and new pipelines, it’s a rare house that has solar panels, and people build new homes, on stilts at least, along the water.

The complacency about global warming comes in part from our disconnect from the environment. Rain and temperature are important to people according to how much or how little difference they seem to make in our lives. Perhaps early farmers and hunters, closer to the earth, would have reacted more readily to predictions of hotter summers or worse flooding. But in American suburbia, environment is mostly background. Weather is good or bad, a day is “beautiful” or not. The climate doesn’t feel closely connected to the food we buy or how well our houses keep us warm. Climate of course intrudes when storms hit or temperatures are extreme, but otherwise our human world is just that—a world settled and run by humans, not one bounded by nature.

We know better. We need to heed the data and find the will to act. We won’t have the fall of the Soviet Union to help get us through this time.