A Common Destiny

Plants make all forms of higher life possible.

The first algae scum probably formed on land 1.2 billion years ago and it took another 800 million years for the first land plants to appear.  800 million years … that’s beyond my capacity to imagine. To put it in perspective, it has been calculated that if you counted to one billion, working eight hours a day, five days a week, spoke aloud every number and started at the beginning of the Christian era, you would not yet be finished.   Put another way, it takes a clock 31.7 years to tick 1 billion times. 

40 million years later these primitive land plants began to diversify and their petrified remains are found today in volcanic springs with their cellular detail clearly preserved. 

The establishment of a land-based flora caused oxygen, a waste product for plants,  to accumulate in the atmosphere. When this concentration rose above 13%, wildfires became possible, as documented in the fossil record some 440 million years ago by charcoalified plant fossils.

400 million years ago  most of the features recognizable in plants today were present, including roots, leaves and secondary wood, and 50 million years later seeds had evolved enabling  plants to reached a degree of sophistication that allowed them to form forests.  It was early in this period that the oldest definitive insect fossil is found, estimated to be 396-407 million years old, and 50 million years later amphibians, from which mammals would evolve, were common.

A report in Science describes an international effort to map the thousands of physical traits and genetic clues that trace the lineage ofall the placental mammals – a huge group of 5000 species. The results indicate that we, together with whales, elephants, dogs and  bats, arose from a small, furry, insect-eating animal that lived after the demise of dinosaurs.

Simple flowering plants probably first appeared 200 million years ago, proliferating 100 million years later in the angiosperm revolution, during which time a species of hunting wasp developed a taste for nectar, became a vegetarian and gave rise to the modern honey bee. 

The latest major group of plants to evolve were the grasses, of which there are some 10 000 species. They first appear in the fossil record about 80 millions ago and became prolific around 40 million years later. Over the last 10 million years the grasses, as well as many other groups, have evolved new mechanisms of metabolism to survive the low carbon dioxide and warm, dry conditions of the tropics.

Flowers, like trees, are rooted in one spot and thus rely on other agents to transport their seeds.  The wind, birds and insects are major actors, and plants evolved to attract them by color, odor and thin stems that wave in the breeze.  The honey bee in return developed the ability to see infra-red colors which direct her to the center of the flower where the nectar is contained and protected, and in so doing she collects and transports the male pollen for pollination. 

Pollen possesses two characteristics that make it particularly useful for studying plant evolution:  it is resistant to decomposition and so can be found in ancient soils, and under the microscope it is very distinctive between plant families and species. An examination of the contents of fossilised dung of plant-eating dinosaurs, for example, revealed types of cells that are only found in the epidermis of grass leaves; thus presumably the last of the dinosaurs dined on grass.

10 000 years ago human intervention played an important role in  plant evolution in the form of the neolithic shift from an economy based on hunting and gathering to a system based on the domestication of plants and animals. Early farmers, for example, selected forms of wheat that could be easily husked, making the flour-making process more manageable, and in so doing inadvertently hybridized different strains.

 So yes, plants are important. First, they take in carbon dioxide and emit oxygen, vital to the survival of most living species.  Secondly they are crucial to both water and soil quality – think of the desertification of the soil and the fetid, rancid water that occurs when plants are absent.  Ken Burns’ documentary, The Dust Bowl, illustrates this dramatically. Thirdly, when plants die they decompose back into the soil, providing a source of nutrients to sustain further life.

Plants are the major food source for most insects, reptiles, birds and mammals, which in turn provide a food source for those higher up the chain, humankind included.  And diversification is important.  We know, for example, that whereas honey bees can survive on one pollen source, to be healthy they need a variety of sources, each with its own specific chemical composition.

“Our mistake,” according to Wendell Berry talking on the Diane Rehm show in 2014, “is that we think we can save the people by abusing the land.”  Not  only does population growth place more demands on decreasing areas of farmland but the urban revolution of the last one hundred years has removed most of us from an intimate awareness of the health and well being of that land.  Beekeeping is a profound and frequent reminder of the vital connection between one species of insect and the land.   It might even be an ominous connection because, as Wendell Berry added, “We all share the same fate.”