Stepping out of the WABAC Machine and looking around we survey a very different planet.
In the early Eocene our familiar continents were scrambled from their present positions. The Arctic sea was inland, almost entirely cut off from the one great ocean, communicating by a long river through present-day Turkey. This meant that ocean mixing — and deep water currents such as the Gulf Stream — did not occur then as it does now.
As the WABAC has deposited us at the present-day North Pole, we rub on our sunblock and venture out through palm trees to the edge of a deep lake covered with a dense green mat of waterfern with lovely, shimmering, purplish-rose tints in the full sun. Below the roots of this fern, trailing downward from its lower surfaces, we detect a stratified water column, going very deep.
With atmospheric carbon above 3500 ppm, the Eocene is about as hot as one could expect Earth to go before it just gives up and becomes a second Venus. High temperatures and winds bring high evaporation, and high carbon deposition increases the density and acidity of the ocean such that a freshwater layer forms on the surface above the much denser saltwater.
River water entering this freshwater layer is rich in minerals, such as phosphorus, which spawn the growth of azolla — today we call it mosquito fern, Azolla filiculoides, Azolla japonica or Azolla mexicana.
In optimum conditions, the foliage becomes so dense it can prevent mosquito larva from developing and hatching, hence the common name. You can find it garden centers because it has become a popular addition to water gardens and ponds. Besides its lovely hue, it forms such a solid mat that it discourages algae growth, feeds fish, scavenges nitrates and helps keep waters clear.
The Eocene was a very warm period — crocodiles at the poles, wherever those were at the time — because concentrations of greenhouse gases were very high. In these favorable conditions, with ample warmth and abundant fertilizer, the azolla bloom doubled its biomass every two to three days. Had that exponential growth curve persisted long enough, the azolla would have theoretically outweighed the weight of Earth (an impossibility) in a matter of decades.
But, following the fate of all exponential growth curves, the azolla was arrested by resource limits — mainly phosphorus — and its own negative feedback.
As they sank to the stagnant sea floor, the dead azolla leaves and roots were incorporated into the sediment; the resulting drawdown of carbon dioxide helped transform our world from the "greenhouse Earth" Eocene to the "icehouse Earth" it has been ever since.
Like it or not, with all the baggage industrial civilization carries, we could get there again. Our emergent Anthropocene unpleasantness is entirely avoidable. We just have to step up photosynthesis. Compared to expensive, unreliable, harebrained schemes to put mirrors into space to block the sun or salt the atmosphere with sulfur, re-greening Garden Earth is safe, clean and too cheap to meter. It also gives us food and oxygen.
The magic of this tiny little water plant, like that of present day permaculture plans for food forests and re-treeing the Sahara, lies in its capability to suck enough carbon and nitrogen out of the atmosphere to cool the planet while supplying us both food and breathing space. It can allow us to return our home to the more hospitable Holocene conditions in which mammals developed a larger cerebral cortex and then monumental civilizations.
Do-overs on this scale are rare good fortune. Let us hope, in the unlikely event world leaders at the UN next week opt to go this route, that they and we will learn from our past mistakes and not repeat them the next time around. But we are getting ahead of ourselves.
Azolla has been deemed a "super-plant" because it can draw down as much as a metric ton of Nitrogen per acre per year (0.25 kg/m²/yr) and 6 tons of Carbon (1.5 kg/m²/yr). Its main limit to growth is the availability of Phosphorus. Each individual plant is 1-2 cm across, green tinged pink, orange or red at the edges, branching freely, and breaking into smaller sections as it grows. It is not tolerant of cold temperatures, and in temperate regions it dies back in winter, surviving by means of submerged buds.
Blooms alone are not enough to have any significant atmospheric chemistry impact; to reverse CO2 and NOx imbalances, the excesses must be sequestered. In the case of the present, this means turning biomass that would, left to its own devices, become atmospheric pollutants such as carbon dioxide, methane, and nitrous oxides into water vapor, recalcitrant carbon and fixed nitrogen. We can accomplish that through the magic of biochar.
In the Eocene Azolla Event, the strategy was different. Dead azolla plants had to be buried and the remains made inaccessible to decomposing organisms. The anoxic bottom of the Arctic basin, a result of the stratified water column, permitted just this: the azolla sat in the mud, unrotted, until it was buried by sediment and incorporated into the fossil record. Today that layer is about 8 meters thick, or about one meter for every hundred-thousand years.
As we write this, oil drilling rigs from Russia, Canada and Exxon are plying the Arctic Ocean dragging tethered Geiger meters. Because radioactive isotopes of potassium were absorbed when the azolla plants were alive and are now a component in their clay content, and because their high cation exchange capacity causes them to absorb uranium and thorium, the fossil azolla layer can be detected in the form of a gamma radiation spike.
Calibration with the high-resolution geomagnetic reversal record with Azolla's gamma radiation signature allows the duration of the event to be estimated at 800,000 years. That time frame coincides precisely with a steep decline in carbon dioxide levels, which fell from 3500 ppm in the early Eocene to 650 ppm after this event.
Thanks the azolla bloom, the Arctic cooled from an average sea-surface temperature of 13 °C to today's −9 °C. For perhaps the first time in its history, the planet had ice caps at both poles. This was not good for the Azolla bloom and so it could not continue its weight contest with the planet.
Gathering some of this magic fern from the Eocene Arctic, transporting to present and diseembarking from the WABAC once more at the Ecovillage Training Center, we are seeding azolla into our constructed wetlands, where it will devour the phosphorus made available from the showers and sinks in the Prancing Poet Ecohostel and commence sucking CO2 and N from the atmosphere, making us even more greenhouse-gas negative than we already are. Since it won't tolerate Tennessee winters we will need to bring some into our other kind of greenhouse before the first hard freeze and then reseed our outdoor ponds again next Spring. Is it edible? Can we feed it to animals? What kind of biochar does it make? How does it function in compost? Stay tuned for further developments.