Chris Maser

It's late afternoon on a clear, warm, sunny September day. A tiny spider climbs a tall stalk of grass in a subalpine meadow and raises its body into the air, almost standing on its head. From spinnerets on the tip of its abdomen, it ejects a mass of silken threads into the breeze. Suddenly, without visible warning, the spider is jerked off its stalk of grass and is born skyward to join other spiders riding the warm afternoon air flowing up the mountainside, all casting their fortunes to the wind, like their ancestors in centuries past floating on currents of air from the far corners of the Earth to be the first inhabitants of newly-formed South Sea islands.

Spiders are not the only things borne aloft on currents of air. In 1883, Krakatoa, a small Indonesian island between Java and Sumatra, was virtually obliterated by explosive eruptions that sent volcanic ash high enough above the Earth to ride the world's airways for more than a year, affecting the climate by filtering the sun's light. Air also carries the reproductive spores of fungi and the pollen of various trees and grasses. It carries dust and microscopic organisms. And it carries live-giving oxygen and water and death-dealing pollution—the legacy of human society. Air can therefore be likened to the key in the Chinese proverb:  "To every man is given the key to the gates of heaven and the same key opens the gates of hell." In this case, air is the key, which carries both life-giving oxygen and death-dealing pollution.

We, however, take air for granted. To take something "for granted" is to be certain of the status quo—an impossibility in a world of infinite novelty. For example, if you could travel back the Archaean Era (3.8 to 2.5 billion years ago), you would not recognize Earth as the same planet you inhabit. By that time, however, the Earth's crust had cooled enough for rocks and continental plates to begin forming. The atmosphere was likely composed of methane, ammonia, and other gases that would be toxic to most life today. Yet, it was early in the Archaean Era that life first appeared on Earth, as attested by oldest fossils of cyanobacteria bacteria (often thought of as "blue-green algae") that date back to roughly 3.5 billion years ago, and are still among the oldest fossils known. Concentrations of atmospheric oxygen rose from negligible levels to about 21 percent of that present today and can be attributed to the cyanobacteria, which have also been tremendously important in shaping the course of evolution and ecological change throughout Earth's history.


This increase in oxygen is thought to have occurred in six steps, measured in billions of years: 2.4, 2.45, 1.8, 0.6, 0.3, and 0.04 billion years ago, with a possible seventh step 1.2 billion years ago. The first step appeared to have been a decrease in the amount of dissolved nickel in the sea water, which could have stifled the methane-producing bacteria and set the stage for oxidation of the Earth's atmosphere because the methane would have reacted with any oxygen and created carbon dioxide and water. The initial change in the Earth's atmosphere took place 2.4 billions years ago, in what scientists call the Great Oxidation Event.

The timing of these steps coincides with the amalgamation of Earth's landmasses into supercontinents. The collisions of continents required to form supercontinents produced huge mountains, which eroded quickly and thereby released large amounts of nutrients into the oceans, such as iron and phosphorus. These nutrient pulses led to explosions of algae and cyanobacteria that, in turn, caused marked increases in photosynthesis and thus the production of oxygen. Enhanced sedimentation during these periods buried large amounts of organic carbon and pyrite, which not only preventing their reaction with free oxygen but also led to sustained increases in atmospheric oxygen.

In fact, much of the oxygen in the atmosphere we depend on was generated through the photosynthesis of cyanobacteria during the Archaean and Proterozoic Eras, the latter of which occurred 2.5 billion to 543 million years ago. Moreover, the beginning of the Middle Proterozoic (16 million years ago) saw substantial evidence of oxygen accumulating in the atmosphere.1 Nevertheless, some of the first creatures to leave the ocean and venture onto land may have been sea-dwelling arthropods whose shells protect their delicate gills in a small reservoir of seawater, which prevents them from drying out, like the hermit crabs of today.2

Everyone knows that land-dwelling creatures, from insects to amphibians, reptiles, birds, and mammals require oxygen. What most people probably do not think about is that all terrestrial plants require air for life, whether they have chlorophyll or not. Green plants use the chlorophyll molecule to absorb sunlight and use its energy to synthesize carbohydrates (in this case, sugars) from carbon dioxide (in the air) and water (ultimately transported from the world's oceans). This process is known as photosynthesis, where photo means "light" and synthesis means the "fusion of energy," which is the basis for sustaining the life processes of all plants. The energy is derived from the sun (an original input) and combined with carbon dioxide and water (existing chemical compounds) to create a renewable source of usable energy.

In addition, plants need soil in which to grow and we need plants as the basis of our food chain. And both plants and animals require fertile soil. In turn, healthy soil has spaces filled with air between the particles and chunks that comprise its matrix. These pockets of air are created by all the organisms living in the soil—from microbes to larger animals, as well as the roots of plants. Most of these organisms depend on the availability of air and water moving through the soil in order to perform their vital, ecological functions that, in concert, create and maintain the soil's health and so that of a forest, grassland, alpine meadow, or desert. In this sense, healthy soil acts more like than a sponge than a brick because air normally constitutes half or more of its total volume.

To clearly understand this, fill a gallon pail with intact, forest soil or other friable soil. If you then compress it, you will find that at least half of the volume was air. Just as we humans require air to breathe, so does every living thing in the soil. Clearly, therefore, compacting the soil, which eliminates the air and thereby increases the soil's density, is suffocating to everything that must breathe in order to live.

Compaction of soil also reduces its ability to absorb and store water, which simulates a drought for those organisms that do survive the initial compression of their habitat, particularly in fine-textured clays and silts. Over time, compacted soil is more prone to actual drought than is healthy, friable soil.3


A "lammergeier" or bearded vulture soaring at 12,000 feet (3,658 meters) on Phulung Ghyang, Newakot District, Nepal, in May 1967. It's a male with an 8-foot (2.4-meter) wingspan.

Meanwhile, above ground, air acts as a cushion, thereby allowing flight. The shape of a wing, be it that of a butterfly, a bird, or a bat is termed an airfoil. As the butterfly, bird, or bat moves through the air, the air goes above and below their wings simultaneously. Air flowing over the upper surface of the wing has to move farther than that flowing below the wing. For both streams of air to meet at the edge of the wing at the same time, the air flowing over the upper surface has to move faster than that flowing below the wing. Because the upper stream of air has to move farther than the lower stream, it exerts less pressure than the air flowing under the wing. This difference in pressures creates the lift that allows flight by acting as a cushion that supports the flying insect, bird, or bat. The speed wherewith an organism flies and the curvature of its wing increases the lift it experiences. In addition, some birds take advantage of the upward movement of warm and then glide downward on the constantly rising current of warm air, called a "thermal."4 Once the aerodynamics of flight were understood, people invented the fixed-wing airplane—beginning with a propeller driven aircraft and progressing to a jet. Then, copying some elements of the basic design and flight dynamics of a dragonfly, the helicopter was born.

Although some animals cannot fly per se, they can use air as a cushion on which to glide, such as flying frogs, flying lizards, a flying snake; flying squirrels, flying phalangers, and flying lemurs.

Flying Frogs:   There are two arboreal frogs in Indo-Malayan region of Southeast Asia adapted to life in trees high above ground. They have enlarged hands and feet, full webbing between all fingers and toes, lateral skin flaps on the arms and legs, and reduced weight. In addition, they have suction pads on their webbed feet, which helps their balance the high trees. These morphological adaptations contribute to a frog's aerodynamic abilities.5 In gliding, they descend at an angle of less than 45 degrees from the horizontal.6

Flying Dragons:   Flying dragons are gliding lizards indigenous to the southwest tropical forests of India and Asia, including Borneo, Java, Sumatra, Sulawesi, and Timor. They also occur in Thailand, western Malaysia, and the Philippine Islands. These slender, long-legged lizards (mostly about 8 inches long, 20 centimeters) have five to seven elongated ribs that fold along the body when at rest. However, when jumping into space from a tree, their ribs move outward to expand the fold of skin and form a wing-like structure, which allows them to glide downward between trees. They can travel up to 30 yards (9 meters), using their tapering tails as a rudder to steer. Just prior to landing, they rise up and stall at precisely the right moment to make a gentle landing, after which they scamper upward in preparation of their next glide.7

Flying Snakes:  Flying snakes, which are found from western India to the Indonesian archipelago, are gliders that use strong updrafts, the speed of free fall, and contortions of their bodies to catch the air and generate lift. To prepare for take-off, a snake slithers to the end of a branch, and dangles in a "J" shape. It then propels itself from the branch with the lower half of its body, which it quickly forms into an "S," while simultaneously flattening its body to about twice its normal width, which gives its normally round body the shape of a concave "C," which traps air. Then, by undulating its body back and forth, the snake actually make turns. Technically speaking, flying snakes are better gliders than their more popular mammalian equivalents, such as flying squirrels. These snakes use their aerobatics to move from tree to tree without having to descend to the forest floor. The smallest species reach about 2 feet (61 centimeters) in length, whereas the largest grows to 4 feet (1.2 meters). Mildly venomous, they have tiny, rigid fangs at the back of their mouth, rendering them harmless to humans.8

Flying Squirrels:  Flying squirrels, which occur in North America and Asia, have furred membranes extending along the sides of the body from the forelimbs to the hind limbs. In members of some genera, the membrane extends from the neck to the tail. At the outer edge of the wrist, the gliding membrane is extended by a cartilaginous projection that acts as a spreader. These squirrels are noted for their ability to glide.

They climb to an elevated point and launch themselves. As they leap into space, they extend their legs outward from the body. Such action erects the cartilaginous projections on the outside of each wrist. These projections help spread the large, loose folds of skin along the sides of the body so that a monoplane is formed, allowing the squirrel to glide gently and quietly with good control. Steering is accomplish by raising and lowering the forelegs. The tail, flattened horizontally, is used as a stabilizer to keep them on course.

An adult northern flying squirrel. These squirrels are nocturnal, which accounts for the eyeshine captured in this USDA Forest Service photograph by Jim Grace

Before a squirrel starts its glide, it examines the chosen landing site carefully by leaning to one side and then to the other, possibly as a method of triangulation to measure the distance. As a squirrel reaches a landing point, normally the trunk of a tree, it changes course to an upward direction by raising the tail. At the same time, the forelegs and hind legs are extended forward, allowing the gliding membrane to act as a parachute to slow the glide and to absorb the shock of landing. The instant a squirrel lands, it races around the tree's trunk, thereby eluding any predator that may be following it, such as the northern spotted owl, which inhabits the ancient forest of western North America and whose favorite meal is the northern flying squirrel. To make another glide, the squirrel dashes to a higher position with incredible swiftness and agility and again launches itself into space. From a height of about 60 feet (18 meters), a squirrel can glide about 163 feet (50 meters) at a rate of six feet (two meters) per second.9

And speaking of flying squirrels, I once saw a gray-headed flying squirrel glide on a moonlit night on Phulang Ghyang, a mountain in the Newakot District, Nepal. The squirrel traveled a good 150 feet (46 meters) down slope from the edge the high-mountain fir forest (elevation of 11,500 feet [3,505 meters]) to a tall snag in the open area of a two- to three-year-old forest fire. It was a truly magnificent sight.

Flying Phalangers:  These phalangers are tree-dwelling marsupials indigenous to Australia, of which the sugar glider is a typical member. The nocturnal sugar glider has folds of loose skin going from its wrists to its ankles. Launching itself from high in a tree, it holds its limbs outward in a spread-eagle fashion, which allows it to glide for distances as long as 330 feet (100 meters). Beside their distinctive folds of skin, these marsupials have grasping forefeet and hind feet; large, forward facing eyes; short, pointed faces; and long, flat tails, which they used as rudders while gliding.10

Flying Lemurs:  Also called "colugos," lemurs, considered to be the closest living relatives to primates, are restricted to the tropical rainforests of Southeast Asia. Flying lemurs are fairly large for arboreal mammals, ranging from 14 to 16 inches (35 to 40 centimeters) in length and weighing from 2 to 4 pounds (1 or 2 kilograms). They have moderately long, slender limbs of equal length front and rear; a medium-length tail; a small head; large, front-focused eyes, which give them excellent binocular vision; and small, rounded ears. But their most distinctive feature is the membrane of skin that extends from the shoulder blades to the fore-paw, from the tip of the rear-most finger to the tip of the toes, and from the hind legs to the tip of the tail. Unlike other known gliding mammals, even the spaces between the fingers and toes have webs, much like the wings of a bat, which increase the total surface area. The gliding membrane, called a "patagium," is as large as is geometrically possible, which gives these lemurs the most extensive adaptation to gliding of all mammals. However, because they lack opposable thumbs and are not especially strong, they climb in a series of slow hops, all the while gripping the bark with their small, sharp claws. But once airborne, they and can glide between trees as far as 230 feet (70 meters) apart with minimal loss of altitude.11

Oregon Red Tree Vole:  The Oregon red tree mouse "parachutes" rather than glides, which means it can only descend at angles greater than 45 degrees, but nevertheless uses air as a cushion to ease its descent. This mouse occurs only in western Oregon in the United States from the crest of the Western Cascade Mountains westward to the shores of the Pacific Ocean and from the Columbia River along the Oregon-Washington border southward to the vicinity of the border between Oregon and California. Adult tree mice range from 6 to 8 inches (15 to 20 centimeters) long, including their tails, and weigh from about 1 to 1 1/2 ounces (28 to 43 grams). The fur on their backs varies from brownish red in the northwestern part of their range to a more orangish red in the southern part of their geographic distribution. Their undersides are light gray, and their long, hairy tails vary from rich medium brown to black.

An adult red tree mouse (more properly termed a "vole." (Photograph by Ken Gordon and Chris Maser

Primarily inhabitants of coniferous forests, mainly Douglas-fir, these mice occasionally live in mixed coniferous-deciduous forest. On being evicted from their arboreal nests, which range from about 20 feet up in a tree to over 150 feet up (6 to 46 meters), the mice often move head-first down the trunk and, if they reach the ground, either go into a handy burrow or under available debris. Otherwise, they may go out onto a branch, cross to an adjoining tree, and suddenly stop, crouch, and remain motionless. Such behavior, along with their small size, is protective because their reddish pelage blends into the dimly lighted surroundings so well that they are difficult to see when motionless. In deep twilight, when they begin to be active, a motionless tree mouse is almost impossible to find among the branches because red is one of the first colors to fade or become neutral as darkness approaches.

Some tree mice, usually adults, launch themselves into space when confronted by a predator instead of going onto a branch or down the trunk of the tree. Although many have their falls broken by lower branches, to which they are adroit at clinging, others merely parachute to the ground. In so doing, they almost invariably land on their feet—uninjured. During free-fall, they spread their legs out, slightly arch their bodies to capture the air cushion with their underside, and use their tail for balance as they descend almost straight to the ground. Some mice parachute from as high as 60 feet (18 meters) up in the trees, land on their feet, and head for the nearest cover. Age, and perhaps a degree of learning, seems necessary before such a feat can be accomplished successfully, however, because young mice seldom land on their feet. They appear to lack the ability to spread their legs and do not seem to have control of their tails; thus, they land on their backs, although I have never seen one injured by doing so.12

In addition to animals using cushions of air for travel, myriad plants ride the zephyrs, some with their seeds dangling from parachutes of various sizes but with a similar pattern of construction, such as dandelions and salsify. Others are small, cottony seeds that float lightly on the breezes; cottonwoods and fireweeds are examples. Still others spin to earth with a seed attached to a large, single wing, such as maple and ash trees.


  1. The preceding discussion of the origin of oxygen on Earth is based on:  (1) Ian H. Campbell and Charlotte M. Allen. Formation of Supercontinents Linked To Increases In Atmospheric Oxygen. Nature Geoscience, 1 (2008):554-558; (2) Introduction to the Archaean. (accessed on Aporil 12, 2009); (3) Bacteria: Fossil Record. (accessed on April 12, 2009); (4) Introduction to the Proterozoic Era. (accessed on April 12, 2009); (5) Pennsylvania State University. Deep Sea Rocks Point To Early Oxygen On Earth. (accessed on April 12, 2009); and (6) Ernesto Pecoits, Stefan V. Lalonde, Dominic Papineau, and others. Oceanic nickel depletion and a methanogen famine before the Great Oxidation Event. Nature, 458 (2009):750-753.

  2. James W. Hagadorn and Adolf Seilacher. Hermit arthropods 500 million years ago? Geology, 37 (2009):295-298.

  3. The foregoing discussion about soil is based on:  (1)Elaine R. Ingham. Organisms in the Soil:  The Functions of Bacteria, Fungi, Protozoa, Nematodes, and Arthropods. Natural Resource News, 5 (1995):10-12, 16-17 and (2)Michael Snyder. Why is Soil Compaction a Problem in Forests? North Woodlands, 11(2004):19.

  4. Cislunar Aerospace, Inc. Aerodynamics of Animals—Birds. (accessed on March 27, 2009).

  5. Sharon B. Emerson and M.A.R. Koehl. The Interaction of Behavioral and Morphological Change in the Evolution of a Novel Locomotor Type:  "Flying" Frogs. Evolution, 44 (1990):1931-1946.

  6. Sharon B. Emerson, Joseph Travis, and M.A.R. Koehl. Functional Complexes and Additivity in Performance:— A Test Case with "Flying" Frogs. Evolution, 44 (1990):2153-2157.

  7. Robert F. Inger. Morphological and Ecological Variation in the Flying Lizards (Genus Draco). Fieldiana Zoology, No 18. (1983) 32 Pp.

  8. Flying snake. (Accessed on March 28, 2009).

  9. Chris Maser. Mammals of the Pacific Northwest:  From the Coast to the High Cascades. Oregon State University Press, Corvallis, OR. (1998) 406 pp.

  10. Flying phalangers. (Accessed on March 28, 2009).

  11. Flying lemurs. (Accessed on March 28, 2009).

  12. Chris Maser. Mammals of the Pacific Northwest:  From the Coast to the High Cascades. Oregon State University Press, Corvallis, OR. (1998) 406 pp.

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