What is the biosphere?
The biosphere –the sphere of life – was named by Eduard Suess in 1875 but not fully described as a concept until the work of Vladimir Vernadsky in the 1920s. The biosphere is made up of biomes, or biophysical zones, filled with many ecosystems each composed of an intricate set of species adapted to the prevailing conditions from below ocean floors and the land surface to above the highest mountains. It includes life forms ranging in size from microscopic bacteria to the gargantuan blue whale. While persistent for billions of years, the biosphere has been hit by five mass extinctions in the geologic past and now faces existential threats to species diversity from human activity.
Coral reef in Papua New Guinea.
Coral reefs are sometimes referred to as the rainforest of the ocean because of the superabundance of life contained within them. All told, 90,000 unique species of marine plants and animals have been indentified in coral reefs.
How does the biosphere work?
Throughout the evolution of life on Earth, from primitive organisms to the present set, all life forms have found ways to obtain energy, acquire nutrients to build organic molecules, and reproduce. Energy from the sun is captured by photosynthesizing organisms called autotrophs, or producers, that can harness solar energy to convert inorganic molecules into organic molecules -- the building blocks of life. These organic molecules store energy and are consumed by other non-photosynthetic organisms called heterotrophs, or consumers. This seemingly simple process -- grass being eaten by deer, for example -- took billions of years to develop. Through the process of evolution, species diversify to fill the available opportunities for existence, creating an ever changing set of plants and animals found in the Earth’s biomes from tundra to rainforests.
Diversity of Life
Life is ubiquitous on Earth, yet biological productivity varies greatly from deserts to rainforests. Some 1.9 million species have been named, but there are an estimated five to thirty million or more species making up the biodiversity of Earth. Many of the unidentified species are in particularly hard to get to places, such as Antarctic ocean environments, or extremophiles living where it is too hot or cold or acidic.
Thousands if not millions of different organisms are teeming below foot and beneath the sea where there just hasn’t been enough time and attention to sort out all these small life forms. Phytomass, or the mass of plants, is estimated to be about 500 to 800 GtC (billion tons of carbon). Estimates of the mass of heterotrophs are dominated by large uncertainties regarding the mass of organisms living in the soil, deep below the soil, and in ocean sediments. Prokaryotes (simple organisms without a nucleus (bacteria and archaea)) alone may equal in mass to that of plants. Land and ocean heterotrophs other than prokaryotes make up a relatively small contribution to the total mass. Estimates of the total mass of the biosphere are more than 1 TtC (trillion tons of C) and perhaps as much as 4 TtC.
Rainforest in Blue Mountains, Australia.
Rainforest in Blue Mountains, Australia. Much of the world’s biodiversity is found in the rainforests scattered about the globe. Despite the vital importance of rainforests to human life and the Earth system as a whole, they are under constant threat from humans who takeover these life-saturated forest for farming and other uses.
How is the biosphere changing?
The suite of species on Earth at any given time are continually changing through the process of evolution. Over geologic time, more species have gone extinct than exist today. A dramatic example of this change is past extinction events. Paleobiologists and geologists have pieced together evidence in geologic record of five mass extinction events reducing the Earth’s biodiversity to a portion of its full potential. A notable example is the mass extinction 65 million years ago that coincided with the end of the age of dinosaurs.
Abrupt change in the physical and chemical factors fundamental to life are key in mass extinctions. After each mass extinction the diversity of life slowly recovers to fill the ecospace available in the Earth’s environment. This process can take millions of years of evolution.
Potential causes for mass extinctions in the past include massive and sustained volcanic eruptions and impacts from comets and/or asteroids – both causing the consequent alteration of the atmosphere from the lofted debris that blocks incoming sunlight. Sustained or very rapid climate change and sea-level change are also possible explanations of past mass extinctions.
Since the last ice age, human activity changing land use has been a dramatic factor in the disruption of species habitat. For example, about 35% of ice-free land is devoted to human agriculture, and as a consequence of this expansion, species are forced into environments in which they are ill suited to survive. Since the industrial revolution, in addition to land-use change, human activity has altered air and water quality and is forcing a change in climate. All these factors interact in complex ways to affect biodiversity. Many scientists consider our present age a 6th mass extinction. An estimate of extinction from future climate change (projected in the range of 3.6 to 5.4 deg F) when compounded by other human impacts to biodiversity, finds that 20 to 30 percent of the identified species known today could be lost along with the ecosystem services they provide.