Living Planet

The chess board is the world, the pieces are the phenomena of the universe, the rules of the game are what we call the laws of Nature.

—Thomas Henry Huxley (1868), A Liberal Education and Where to Find It biocomplexity

Life is the ultimate expression of natural variability. Through the course of the Earth system, organisms have evolved within kingdoms of differing biological complexity from bacteria to the plants and animals. Within each kingdom, organisms are further distinguished across hierarchies of taxonomic complexity (e.g., Table 2.1). Even within unique species—which are defined by their ability to interbreed and produce viable offspring—there are biochemical, physiological, or morphological variations that influence the fitness of individuals to propagate their genes into future generations.

Adaptations also enable species to interact with other organisms within habitats that are constrained by physical, chemical, and geological phenomena (Fig. III). These ecological interactions exist at the population level where individuals of the same species utilize resources within a defined area to increase their density and biomass. Additionally, within habitats, interacting populations of different species form communities that are characterized by their diversities. Different communities subsequently interact within the natural boundaries of a region—forming ecosystems that are further characterized by the flow of organic production. At the pinnacle of species' interactions (Table 9.1), all biological systems unite into the biosphere, which embodies the dynamics of life on Earth.

atoms [Eq. (8.2d)], each of which robs oxygen atoms and effectively destroys around 100,000 ozone molecules:

where UV is ultraviolet radiation; M, catalyst; O, oxygen atom; O2, molecular oxygen gas; and O3, ozone.

Baseline observations from the British Antarctic Survey indicate that levels of ozone centered around 300 Dobson units from 1957 to 1975 and then decreased precipitously to levels less than 100 Dobson units today (Figs. 8.11a). The shape and location of the ozone ''hole'' (Fig. 8.11b) are another reflection of the circumpolar nature of the Antarctic environmental system (Figs. 8.1-8.3 and 8.6). These observations from Antarctica, which confirmed earlier hypotheses about stratospheric ozone depletion, were the harbingers that motivated the international community to eliminate chlorofluorocarbon production by the end of the 20th century (Chapter 11: Environmental Protection).

The mere fact that ozone depletion was detected most severely over Antarctica, far removed from the populated regions of the planet where chlorofluorocarbons were introduced into the atmosphere, alone is a strong demonstration of the global dynamics of the Earth's atmosphere. In addition, stratospheric ozone and carbon dioxide both demonstrate the overall value of long-term measurements, over decades and centuries, for assessing environmental trends and events that can affect society.

The essence of global climate variability is that long-term climate trends (Fig. 6.5) are influenced by shorter-term climate cycles (Fig. 7.4), which are further superimposed on even shorter-term climatic events (Figs. 7.6, 8.9, and 8.10). Distinguishing the underlying forces that influence the dynamics of the Earth system over different time and space scales (Figs. 2.3 and 6.1)—from the movement of continents to the combustion of fossil fuels—is essential to understanding relationships between environmental variability and humankind.

TABLE 9.2 Percentages of Endemic Species among Marine Benthic Groups South of the Antarctic Convergence a

Number of Endemic benthic species

Taxab species (%)

Plant Groups

Number of Endemic benthic species

Taxab species (%)

Plant Groups

Green algae (Chlorophyta)

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