Dr. Gregory J. Retallack is a fossil soil specialist in the University of Oregon’s geology department. On June 15 he spoke before an audience primarly composed of biologists about an idea that may be in vogue with his audience but is not well accepted in his own field.
“The problem with ‘Plant a tree, save the planet’ is that it’s not properly appreciated by geologists.” While allowing that this may be a bit simplistic, he set out to “make a case for the role of life in climate.”
“Plants cool and animals warm the planet,” he said. “I call this a principle instead of a hypothesis or a theory because it’s proven,” he added.
Proserpina is the Roman name for Persephone of Greco-Roman mythology. The daughter of Jupiter (Zeus) and Demeter, she was abducted by Pluto (Hades), who carried her off to the underworld. Her mother, the goddess of agriculture and fertility, went into a hardcore depression and stopped doing her job --- which left the Earth cold and barren --- until a deal was struck. Proserpina would spend half the year in the classical Hell, during which Demeter’s sorrow would subject the world to autumn and winter, and half the year up on Mount Olympus, when her mom would snap out of her funk and give us spring and summer.
The geologist does not look to ancient mythology as an explanation for seasonal and climatic cycles, but he does see a number of short- and long-term oscillations at work.
According to Retallack, spring is the result of months of carbon spewing out from the previous year’s decaying leaves and fruits, while autumn is the result of a whole summer of carbon dioxide being rendered into oxygen through plant photosynthesis. He points to the seasonal cycles in the content of gas bubbles found in the climatic record of millions of years represented by the Vostok arctic ice core samples. He offers analyses of fossilized plant cuticles as corroborating evidence.
As a soil specialist working primarily in North America, he has studied and documented a geologic history of Central Oregon soil layers, which alternate between those with fossilized earthworm tracks (grassland) and those with the remains of cicada burrows (desert sagebrush). “There’s a beat to it,” he explained.
Also moving to a beat are the fossil records of north and south animal migrations corresponding to ice ages and warmer periods.
Looking over an even longer time scale, he notes the occasional catastrophic impact that sends all sorts of burned stuff and greenhouse gases into the air, causing mass extinctions and relatively short-term climate changes, but underlying this there’s another steady beat, a back-and-forth evolutionary competition between plants and animals.
With the advent of plant photosynthesis, the atmosphere became richer in oxygen and poorer in carbon dioxide. But then came plant-eating animals to shift the balance back in the other direction. Then plants developed lignin, the hard stuff that makes trees possible. “Trees created a deeper weathering and rearranged our atmosphere,” he said. But not for long, geologically speaking. Termites and dinosaurs arose to end the unchallenged domination of trees, and shift the atmospheric balance back again.
So what’s the tipping point between the planet’s warm and cold periods? Retallack believes that the critical juncture is when the soil can’t absorb much more carbon.
Another cyclical factor that needs to be taken into account, Retallack explained, is the albedo --- reflective capacity --- of different types of ground circulation. Ice reflects a lot of sunlight back into space, so when the northern hemisphere gets largely covered with glaciers, the entire planet absorbs substantially less heat from the sun and the global cooling trend is accentuated. But short of ice age conditions, a yellowish dry grassland will reflect more light than a green forest but less than a sandy desert.
There are other theories out there, and other factors that must be weighed, but Retallack has a strong opinion about the geologic beat he studies. “I think it’s a biological creation.”
So does that mean that environmentalists from the industrialized countries need to make it their priority to head south and browbeat the Brazilian government into doing a better job of preserving the Amazon forest?
Retallack didn’t get into all the political and biological ramifications of that, but he did say that in the overall global balance, “a tropical forest... is not a big lever.” Far more important, he believes, is what happens in the temperate zones.
Also in this section:
When the Americans brought their medicine to Panama
How figs keep wasps from cheating
Termite evolution
Biological climate control
Interpersonal violence as a public health issue
