In the next few parts of our journey through the solar system, we examine our world through the eyes of a stranger, seeing past the assumptions that blind us to the awesome complexity around us. Earth is a lot more than the birthplace and currently unique home of humanity, but a world of rich diversity where a number of cyclical processes keep a dynamic and precarious balance. One of those processes, life, may ultimately catalyze a transformation of the solar system through the continuing evolution of technological intelligence.
The progress of our adventure so far (current in bold):
1. The Sun
2. Mercury
3. Venus
4. Earth (Vol. 1)
5. Earth (Vol. 2)
6. Earth (Vol. 3)
7. Earth (Vol. 4)
8. Earth (Vol. 5)
9. Earth (Vol. 6)
10. Luna
11. Mars
12. Phobos & Deimos
13. Asteroids
14. Ceres
15. Jupiter
16. Io
17. Europa
18. Ganymede
19. Callisto
20. Saturn
21. Mimas
22. Enceladus
23. Tethys, Dione, and Rhea
24. Titan
25. Iapetus
26. Rings & Minor Moons of Saturn
27. Uranus
28. Moons of Uranus
29. Neptune
30. Triton
31. The Kuiper Belt & Scattered Disk
32. Comets
33. The Stellar Neighborhood
In volumes 4 and 5, we explore the most active, and catalytic layers known to exist in the solar system - the terrestrial biosphere and anthroposphere - two interlocking domains whose increasingly rapid, feedback-driven evolution is changing Earth and may eventually change the solar system as a whole. How exactly that plays out remains to be seen - it may ruin the terrestrial ecosystem, or it may become a spark that ignites life and intelligence throughout the solar system and beyond.
I. Context
II. History
III. Properties
1. Orbital and Rotational Features
2. Size and Mass Characteristics
3. Internal Structure
4. Surface
A. Geography
B. Hydrosphere
C. Biosphere
D. Anthroposphere
5. Atmosphere
6. Magnetosphere
IV. Natural & Artificial Satellites
V. Past Relevance to Humanity
VI. Modern Relevance to Humanity
VII. Future Relevance to Humanity
VIII. Future of Earth
IX. Catalog of Exploration
C. Biosphere
Whatever magical ideas you have about the nature of life, they pale beside a reality far vaster and more awesome. Life - in all its unimaginable diversity - is something that happens in statistical proportions to certain materials when associated together under certain environmental conditions. That may sound dry, but it gives rise to a depth of possibility that can never be completely fathomed: Every individual manifestation is unique, and yet connected to every other; it is evolutionary, and yet recurrent; it has no identifiable beginning or end, but only a continuum of change as energy flows and material is redistributed. We can plumb the depths of its history, but we will never know all the forms it has taken; we can seek to discover new life both on this planet and elsewhere, but we will never find even the tiniest fraction of the cosmic whole; and we can project into the future, but will only ever know it by experiencing it.
In truth, biology is not really a separate phenomenon from the non-living world, but something that arises by the same underlying physics as all other processes: The electrical attraction of an electron to a proton, the bonding of one atom to another by this force, the solvent properties of water (see molecular discussion of water in Vol. 3 of the Earth sub-series), and the ability of large molecules to break apart and recombine in novel forms in the presence of the right amount of energy. Even the assumption that life must involve chemical elements is purely a matter of logical parsimony, not of positive evidence: We have no specific reason to believe that patterns of complex, recombinant change similar to what we know of as life cannot occur in other physical media.
With this understanding, we begin to dimly glimpse the infinity of possibilities that surround us - surely most of which are unrealized, but undoubtedly some of which exist without even being imagined. In my personal view, life is all around us, but we must let go of many assumptions to recognize it - but that is an abstraction beyond the scope of this particular discussion. On Earth, life (often denoted as "life as we know it") is a process centered on and arising from replication of deoxyribonucleic acid (DNA) chains - very large, delicate molecules composed of pentagonal and hexagonal arrangements of carbon, oxygen, phosphorus, nitrogen, and hydrogen into an overall double-helix structure.
The nature of the relationship between DNA and our intuitive understanding of life is often misstated: We typically hear that DNA "codes for" an organism, but the logic of this statement is backwards. The life we see around us is not the "purpose" of DNA, but a consequence of DNA replicating itself - a byproduct, if you will. Large organisms such as ourselves are a result of DNA chains reproducing themselves, but ascribing purpose to those results would be arbitrary and illogical. Rather than anthropomorphizing a molecule and pretending it somehow "knows" what will happen because it self-replicates, science regards complex living organisms as an emergent property of organic chemistry: A profoundly complex system arising from the large-scale, high-number, long-time interactions of relatively simple components. Scroll down the following images to get a sense of how emergence works:
At first you see meaningless information - squares of color. A single pixel on a TV screen or computer monitor provides a very simple piece of data, and can convey only one of a handful of colors. But in association with a large number of other pixels, that simple piece of information can produce increasingly complex images. It only takes a few dozen pixels to communicate the simplified shape of an Italian plumber from an 8-bit videogame. A real Italian plumber, of course, requires quite a lot more information than that to exist, but the principle is the same: We see an Italian plumber when what is actually happening are billions of chemical interactions occurring on millisecond timescales, all as part of a feedback loop of DNA replication. We see the wave and not the water, because we are waves ourselves.
DNA interacts with a wide variety of other molecules in the course of self-replication. One type, ribonucleic acid (RNA), is a nucleic acid like DNA despite being chemically different, and can itself form the basis of quasi-lifeforms such as viruses that hijack DNA to replicate themselves. However, the fact that we do not observe anything more complex than a virus based entirely on RNA indicates that it lacks the capability to be the basis of life under terrestrial conditions, and most likely under any conditions since greater extremes either prevent the molecule from existing (high-energy environment) or prevent it from interacting (no liquid medium).
A wide array of proteins are also crucial to life, and occur in such variety and abundance in biology that prior to the understanding of DNA's role it was assumed that proteins contained the genetic code. However, we now know that DNA generates proteins, and they in turn function as machinery that serves to benefit reproduction of the DNA molecule: Some break apart other molecules, some put molecules together into larger ones, and some perform elaborate combinations of these roles in dealing with various chemical compounds. In fact, the mechanical possibilities of protein molecules are so vast that large networks of computer processors are needed to even explore a few cases of what a single molecule can do (see the Folding@home project for ways you can participate). An animation of a protein molecule folding:
One particularly difficult concept for laymen is the fact that all of this complexity arises from statistics, not from some grand "plan" - these molecules make "mistakes" constantly, but those mistakes are self-correcting because those which accumulate interfere with their own ability to propagate. Meanwhile, mistakes that by chance benefit propagation end up changing the organism and are one of the drivers of evolution. The sheer numbers of molecules involved, and the timescales over which they collectively unfold, are so vast that life as we know it is not merely probable under observed conditions, but comes close to being mathematically certain.
This is the reverse of typical religious claims (I will not undeservedly aggrandize them with the label of "arguments") that insist life is improbable without some prior intelligence directing them - the more we learn about our universe, the more we find instead that life is certain to occur as a result of underlying physics. Whether physics are part of some "plan" that a deity stands back and allows to unfold is beyond the scope of this discussion, but I will say that I find such a concept moot.
The fact is that we only see Order in life-as-we-know-it because we arise from it and have evolved organs that perceive the useful patterns amidst the complexity. Imagine that instead of having a brain that perceives these shapes and colors, you perceived each and every molecule in a biological system - then an "elegant" organism like a human would look like a frothing chaos with tendrils extending indefinitely out into the environment rather than a smooth and self-contained lifeform. We can suppose that a hypothetical alien being that did not evolve under similar conditions could look at Earth's biosphere and see nothing more than random "foam" with no necessary indications of orderly processes at work. The lesson is that life may exist in very unexpected places in the universe, and may eventually require a leap of understanding to recognize.
i. Extent
Earth's biosphere is the only one currently known by humans, although there is strong (albeit divided) scientific opinion favoring microbial life on Mars, theorized possibilities about life beneath the ice of Jupiter's moon Europa, and speculation further-afield regarding the complex organic environment of Saturn's moon Titan.
There is evidence of life on Mars (see ALH-84001, and the methane anomaly in the Martian atmosphere) although consensus has not been achieved about the interpretation of that evidence. Similarly, our understanding of Europa has not yet advanced to the point where we can say with certainty that the theorized oceans beneath its ice actually exist - one possibility is that the ice transitions to a viscous sludge rather than liquid water - and they will have to be confirmed before it can be said that Europa is a strong candidate for extraterrestrial life. Titan, despite having amazingly complex chemistry in its atmosphere, is too cold throughout its environment for liquid water, so life as we know it is considered impossible - however, there have been theories that ammonia could serve as a biological basis under those conditions. We have no evidence to that effect, however - our sole confirmed data point regarding life remains Earth.
The terrestrial biosphere largely exists in the top few hundred meters of the oceans, with secondary centers focused on rivers and lakes. This is unsurprising given the fundamental role played by water and energy in facilitating biological processes, so it it makes sense that life is densest a short distance underwater where sunlight can penetrate to feed photosynthetic organisms and form the basis of a food web. Land organisms have to be hardier, because they are required to carry their water internally and not lose it more quickly than they can replenish it. So it is also unsurprising that land ecosystems are densest on coastlines, along rivers, and beside lakes.
What is somewhat surprising is that marine biomass is dominated by animal organisms while land biomass is overwhelmingly in the form of trees and other woody plants. So while solar energy enters the food web through the same process in both cases, photosynthesis, it accumulates in very different places depending on whether the environment is marine or surface. Marine plants and cyanobacteria are basically a thin membrane that feeds a very large and diverse animal biome, while on the surface plants dominate and feed a relatively thin smattering of divergent animal biomes.
Although life is concentrated close to sea level, the biosphere extends all the way to the ocean floor and beneath to unknown depths into the lithosphere, and upwards to uncertain heights into the upper atmosphere. At both extremes, life consists entirely of microbes - in the case of extreme heights, life occurs in the form of organisms that live on grains of material that have been blown by chance into high layers of the atmosphere, but there are not known to be any species that live specifically in those regions. Water is not concentrated or persistent enough in the atmosphere, and nutrient minerals are far too rarefied for there to be dedicated atmospheric biomes. Air is merely a transitory medium for Earth life - organisms move through it on their way to surface or subsurface locations.
There is some speculation among exobiologists (scientists who study the theoretical possibility of extraterrestrial life) that under different conditions, a dedicated atmospheric biome could exist, but those conditions would likely not be amenable to lifeforms such as ourselves - the atmosphere would have to be quite dense, very humid, and some incredibly violent process would have to continuously introduce nutrient minerals from the surface into the air. Again, this is speculation.
ii. Marine Ecosystems
The most abundant lifeform on Earth, the photosynthetic microbe cyanobacteria, forms the basis of the marine food web. They are eaten by simple animals - mostly very small creatures called zooplankton - which are in turn eaten by larger organisms such as fish and crustaceans, that are themselves preyed on by bigger fish, bigger crustaceans, etc., and marine mammals like seals and whales. At the top are apex predators such as orcas and great white sharks. An example of a marine food web:
Marine life depends on both oxygenation and nutrient-enrichment of the waters by interaction with the atmosphere above and surface beneath, so it's no surprise that the richest habitats occur in coastal areas where these three environments interact most closely. In fact, this is a general rule for habitability: Life is most probable, and likely most abundant, at optimum convergences of energy, material, and water (or other liquid theorized to perform a similar function under prevailing conditions). If we could imagine an ideal planet for life-as-we-know-it, it would be uniformly covered by a few dozen meters of liquid water ocean churned vigorously (but not too violently) by winds and tides.
For Earth, the ocean is every bit as diverse in the density of living organisms as land - the open ocean is sparsely-populated compared to the coasts because it's not nearly as nutrient-rich, and there are also "deserts" (dead zones) where the water is oxygen-poor, nutrient-poor, or both, and also man-made deserts due to toxic pollution and food web collapse from over-fishing. Ocean dead zones:
There are also extensive oceanic wastelands called "garbage patches" consisting of pulverized plastic debris and its degraded byproducts that circulate with gyres - circular currents driven by the Coriolis effect. The largest of these is thought to be the Great Pacific Garbage Patch - a region with heavy concentrations of plastic particulates in the upper water column that can absorb toxic chemicals and poison the food web through ingestion and respiration. But even in the absence of toxins, the plastics are being eaten, filling up the stomachs of marine and bird life, and just sitting there taking up space without being passed through the digestive system or contributing anything to nourishment. Some of the toxins absorbed by the plastics end up being ingested by humans through sea food. Because the material has been pulverized, the regions look less like junkyards than a colorful "scum" of confetti. A brief presentation at TED about the garbage patches:
Fortunately, the oceans are quite large and thriving habitats still massive. Some areas, such as off the coast of southern Africa, are so teeming at some times of year they are practically undersea jungles with all manner of marine animals interacting in close quarters. For instance, in the video clip below, we see a sardine run - a phenomenon of unparalleled biodiversity, where ocean currents along the South African coast churn up nutrients that breed high concentrations of plankton, in turn attracting large masses of sardines, which then bring in bigger fish, sharks, dolphins, seals, seagulls, and humans. Aside from the beauty of it, we see an important principle demonstrated: Emergent group behavior. A large school of fish essentially behaves as a single individual, much in the same way that large numbers of individual cells behave as single organisms:
Other marine environments are quite striking for different reasons, such as the plant life (as in kelp forests) or the surface habitats constructed over time by the animals that inhabit them (as in coral reefs). Both are treasured for their beauty, colorfulness, and the diversity of organisms that inhabit them, although this has rarely if ever stopped human activities that endanger them. Kelp have evolved air bladders that allow them to float toward the surface - a trait that may occur above water in other complex living worlds with particular atmospheric conditions where some gas that can be biologically generated would be buoyant.
As on land, intelligence is a rare but observed property in a few marine organisms, although we have no way of knowing to what extent this behavioral complexity translates into a difficult concept like "consciousness." Occam's Razor would suggest that we must simply accept that there is nothing magical involved, and that if it looks conscious, it is conscious - essentially the same reasoning by which we accept that other human beings are in fact beings despite the impossibility of proving it. The two groups of marine organisms where varying degrees of intelligence are observed are cephalopods (specifically, octopi) and cetaceans (whales and dolphins), although the latter, being mammals that originally evolved on land, have a radically different set of traits.
Cephalopods are often highly social organisms exhibiting complex behavior and, in the case of octopi, superb mechanical abilities. An octopus can learn to undo - and, amazingly, rebuild - complicated structures, such as unscrewing bottle caps or using building blocks that fit a certain way to make a habitat for itself. Their bizarre physiology and likely very different way of perceiving reality make them ideal analogs for alien intelligence, although the marine environment has never given them a chance - or provided much motivation - to develop technology. The arms of an octopus, for instance, have some degree of neuronal autonomy: In other words, although they do have a centralized brain, they also have a much more distributed neural mass than vertebrates - each of their arms has a "mind of its own," although very simple and reflexive.
Most cephalopods exhibit bioluminescence for camouflage, although it is possible it may also be used for complex communication among some species. Whether this communication rises to the level of symbolic language is very difficult to know, although the likelihood is against it since it does not appear to be present even in other socially complex non-human species. Nevertheless, there is plenty of evidence that there's a there there, whether or not their intelligence involves symbols or just holistic thinking.
Cetaceans are far more familiar, being dedicated aquatic mammals that evolved from land quadrupeds. Presumably, environmental changes gradually turned them into semi-aquatic, otter-like creatures that then became increasingly exclusive to the water until their forepaws became flippers, hind limbs disappeared, and their tails became finned. Most whales are similar in intelligence to large land-based herbivores like cattle and wildebeest, but the more sociable among them may be on par with elephants. The cetaceans that most interest science are the bottlenose dolphins, which exhibit not only a profound intelligence, but a curiosity and playfulness that often endears them to humans. Their communication, which occurs by ultrasound, may (or may not) rise to the level of symbolic communication, with most evidence suggesting that it either doesn't, or is very primitive, or else involves syntax that humans have not yet penetrated.
However, bottlenose dolphins have shown the ability to understand symbolic communication, and not merely in the sense of one-word commands - they are able to process relationships among words given in sign language, such as nouns, verbs, and time- and sequence-related instructions. They have also shown the ability to understand the meanings of some complete sentences that involve multiple relationships. This should not be mistaken for human-level cognition, since we are able to "borrow" the intelligence of the entire species through millennia of symbolic memory, but it may rise to (possibly even exceed) the level of individual human intellect. Even if they possess symbolic language, dolphins interact in relatively small communities and thus their "culture" is tribal - but their curiosity and apparent benevolence to humans under most circumstances does not signal much in the way of xenophobia. It is the current consensus that bottlenose dolphins are the second most intelligent species on Earth, and efforts are ongoing to develop technology-assisted dialog with them in the wild.
Unembeddable link, fully worth opening in another tab:
http://www.youtube.com/...
Orcas are a somewhat different story from dolphins: As highly-evolved and quite cruel apex predators that feed on other whales, they have violent instincts that belie the cute image they're forced into as captives of marine parks like Sea World. Orcas are still quite curious and intelligent, but it is the somewhat menacing curiosity exhibited by many top predators - the interest in something new that might turn out to be a meal, or just a bit of sadistic enjoyment. Evolution has given them some of the uglier behavior traits of wolves and big cats - taking what appears to be "fun" in tormenting prey as a way to demoralize and weaken its resolve. They can learn to accept humans as members of their pod in captivity, but every once in a while they can get resentful and react violently.
The largest animals ever to exist - substantially bigger than any dinosaur yet known - are currently living in Earth's oceans: The blue whale. Its skull alone, standing on end, is taller than most two-story houses.
iii. Land Ecosystems
While the sea has more life overall, the land has a greater diversity of ecosystems because there are more environmental possibilities - frigid and dry, cool and dry, cool and humid, warm and dry, warm and humid, hot and dry, or hot and humid. These environments change with latitude, altitude, and with the relationship to rivers and air currents, as well as anthropogenic (man-made) factors, but for the sake of simplicity we will distinguish land ecosystems in general from those existing within the anthroposphere (human habitat), which we get into in the next volume of the Earth sub-series. The word terrestrial is often used to denote being land-based, but for this series we will just say "land" or "surface" because "terrestrial" in the wider context of the solar system encompasses the whole planet Earth.
The various combinations of conditions possible on land give rise to a great diversity of biomes - areas with similar overall environments, species, and ecological relationships. Even where geographic isolation has kept two similar areas apart, the species that live there develop similar adaptations to like conditions. Of course, "similar" tends to be a surprisingly sensitive property, as otherwise slight shifts in temperature or water availability can significantly alter the kinds of organisms that dominate. Hence the large number of distinct ecosystems on the land area of a single planet where land is (currently) only 29% of the surface:
Not much lives in the "Ice sheet and polar desert" land biome - even the so-called polar bears and Emperor penguins are not associated with the actual poles, as these areas are extraordinarily cold and dry even compared to their normal habitats, and do not provide access to the coastal food they eat. They do, however, populate the fringes of the biome, on the edges of ice sheets where there is access to fish, seals, and other prey. A few birds also live on these fringes, but for the most part this "biome" is almost a misnomer, with whatever life being largely microbial, sub-surface, and possibly analogous to what we might expect on Mars.
Not only are they the coldest places on Earth, but they are bathed in ultraviolet radiation as a result of the polar ozone layer holes, and also experience the highest particle flux from the solar wind and cosmic rays due to the planetary magnetic field. It sometimes puts on a spectacular light show in the upper atmosphere (the auroras - we'll get to them in subsequent parts of the sub-series), but there's rarely anyone or anything present to appreciate it. Typical views of such regions:
A polar Arctic food web:
Antarctic food web:
Note that not much of these polar food webs impinges on land - they're both overwhelmingly bound to the sea, which means they only occur on the fringes of the ice sheet. Not a damn thing actually lives on the ice as a committed habitat, because there is no photosynthetic life to form the basis of a food web - every animal in this biome depends on the sea.
Tundra is more habitable, if only marginally so - it comprises Arctic and sub-Arctic regions warm enough for hardy shrubs, grasses, mosses, and lichens, with a few cold-adapted migratory herbivores such as caribou (or reindeer), Arctic hares, and predators that prey on them such as various Arctic wolves and foxes. There are, by definition, no trees in a tundra biome - if trees appear in any significant quantity, then the climate has changed and the area is no longer tundra. Since the sub-soil is usually frozen in permafrost, melting of the upper layers in the brief warm season makes tundras moist and boggy, which may seasonally attract some species of birds.
An example of a tundra food web:
Alpine tundra - that is, tundra existing at high altitude, regardless of what kind of biome exists in the adjacent lowlands - is similar to high-latitude tundra, but differs in that it's typically less boggy because of the sloping gradients and has even less wildlife. Mountain goats, llamas, alpacas, and yaks are examples of the very sparse fauna.
Taiga (first syllable rhymes with "pie"), also known as boreal forest, is the largest land biome on Earth, encompassing most of Canada, Alaska, Russia, and Scandinavia. Sometimes taiga is distinguished from boreal forest, with the former being the label for the borderlands between boreal forests and tundra - i.e., sparser, stunted trees - but they may also be used as synonyms. It is overwhelmingly composed of conifer trees, with the animal life, though more abundant than that on the tundra, still relatively sparse compared to lower latitudes and either migrates or hibernates during winter. Even in Summer, the Northern regions of the taiga can be silent, spooky, and gloomy places where the only sounds are the wind, an occasional creak of a tree, or rarely the cry of a hawk or the hoot of an owl. Still, quite a few animals live there - e.g., bears, wolves, wolverines, caribou, deer, beavers, squirrels, hares, fish, insects, and so on.
The temperate broadleaf forest or mixed forest has layers of vegetation, with mature trees forming the canopy, smaller or younger trees beneath, then woody shrubs, and finally ground-cover plants. These biomes are called "mixed" because they can include conifers, but the trees are largely dominated by broadleafs. They tend to be seasonal, and as a result produce remarkable colors in autumn as leaves begin to die. Most of the same animal life that abides in boreal forests also lives here, in addition to a much broader array of other species that would have difficulty tolerating the harshness of the taiga. The Eastern United States and most of Northern Europe is dominated by this biome.
Temperate rainforests occur in regions with cool, humid climates such as the Northwestern United States, and are known for having the largest trees on Earth both by height and by mass. Coast redwoods are an example of a notable tree found in temperate rainforests, although conifers in general are typical, and other types of temperate-climate trees are present. Bears, foxes, wolves, deer, squirrels, hawks, and various other species along those lines are often well-represented, and the environment tends to be popular with humans as well for visitation (though less so for habitation due to the dreariness of the cold damp). Some examples:
More famous, and arguably more important to the terrestrial biosphere, are the tropical rainforests - hot, humid environments within 28 degrees of the equator where Earth's biodiversity is at its maximum. These regions teem with plants of every shape and size, microbes, fungi, insects, arthropods, fish, amphibians, reptiles, birds, and to a lesser extent mammals. The mammalian order is oddly underrepresented amid hot humidity, perhaps because its metabolic advantages are best suited to places with some level of challenge - be it semi-aridity or somewhat cooler temperatures - where less advanced species have a harder time. Microbes, insects, fish, and birds, however, are explosively diverse in these environments.
Most of these rainforests are found in close association with large rivers (e.g., the Congo and the Amazon) fed year-round by the heavy rainfall. Vegetation in the thickest parts of the forest may be dense enough to effectively blot out the Sun on the surface due to multiple canopies comprised of various types of trees, vines, and undergrowth. Due to the thickness of plant cover, atmospheric conditions beneath the canopy do not change much seasonally or between night and day, but remain hot and humid. The word "jungle" is a synonym for tropical rainforest. "Subtropical rainforests" are a somewhat related but different environment that is simply less dense than its tropical counterparts, and may encompass heavily canopied areas of hot, swampy wetlands such as the Florida Everglades.
Ferns are heavily represented, and tend to have much bigger fronds than in occurrences under other conditions. Tree leaves in general are bigger than elsewhere to catch more sunlight, as the main limitation on light availability is other trees rather than weather, and this abundance of leafy material in turn helps feed a very dense insect population. While seasonal trees may be found in a few spots, the tropical rainforest is green year-round, and not much in the way of large-scale migratory behavior occurs among its animal constituents (there is no need). Tropical rainforest images:
The jungle is, of course, home to several species of evolutionary interest to this discussion: Most notably, primates - both monkeys and great apes. Some human communities are also native to rainforests, although both they and their environment are being displaced by other humans who have grown accustomed to drier and more open (savanna) conditions. The displacement of humans may at least be offset in some ways if local peoples are given a share of the benefits of development, but for the non-human primate inhabitants, there is no trade at all: They simply cease to be viable when their habitat is lost, and end up starving to death, contracting diseases, or are decimated when they try to survive by stealing food from humans who may also be struggling. Examples of non-human primates associated with (but not necessarily limited to) tropical rainforests:
There has been a lot of research over many decades on ape intelligence, and the consensus seems to be that the most intelligent non-human primates are the chimpanzees (chimps), although gorillas are considered a close second if not more or less comparable. Both can learn simplified sign language to a degree and show many of the standard indicators of self-awareness, but in recent years have been surpassed by bottlenose dolphins in how far this is thought to go.
Still, there are complications in making such assessments, given that apes are a lot more like humans - and thus their thinking is more likely to resemble ours - so comparing two or more non-technological intelligences to each other presents difficulties. For instance, apes may use sticks to collect ants for food or smash nuts with hard objects, so some researchers label this "tool use," but dolphins do not live in an environment conducive to that type of object-manipulation - and yet they are highly able to learn to manipulate objects in captivity, and show creativity in adapting the techniques they learn unparalleled among non-human animals. Nonetheless, great apes are quite advanced relative to other large mammals.
In particular, great apes have been shown not only to learn nouns and verbs of sign language, but to transmit these signs to their children. Syntactic understanding is not on the level that dolphins have shown - e.g., not as advanced in creatively interpreting instructions or understanding abstractions - but shows clearly that thought on some level is taking place. Some videos on ape intelligence:
The next biome we will look at is the tropical dry forest - forested areas in the tropics and subtropics that experience a significant dry season. The biota share some overlap with both tropical rainforests and savannas, but the vegetation is less dense and the colors somewhat muted, with the addition of some types of trees with adaptations against the dry season. Temperatures are still quite warm year-round, so the main environmental challenge to the biosphere is the seasonal drought that interrupts otherwise frequent rainfall.
One consequence of this, and one of the biggest distinctions is that many trees are deciduous (they shed leaves seasonally), so during the dry season a dry forest will look somewhat bare and brown, but will still have green here and there. For the same reason, the branches on the trees may be skinnier and the forest may seem "threadbare" in comparison to a rainforest. Moss is far less represented, and the ground beneath the canopy is dustier - at least in the dry season. In terms of fauna, it serves as a bridge between the rainforest and drier biomes. Some distinctive images:
Savannas are considered a single biome in general, but are also divided into two categories based on whether the climate is temperate or tropical/subtropical. In both cases the land is more or less flat and semi-arid to semi-humid, with sparse trees, marshes, shrubs, and grasses. The African savanna is notable for being the epicenter of non-human mammalian life, where huge numbers of species live and interact, and also the birthplace of the hominid line, where our ancestors left the trees and adapted to moving long distances across the open land. These biomes are home to enormous densities of insect life and birds, as well as large migratory herbivores and the predators that hunt them.
You may have seen or heard of the famous Battle at Kruger video, where a three-way brawl between bison, lions, and crocodiles at South Africa's Kruger National Park was captured and uploaded to Youtube - a real lesson in savanna politics:
The Mediterranean vegetation biome is characteristic of the Northern Mediterranean coast, and also happens to be commonplace where I live, in Southern California. It comprises chaparral scrublands and semi-arid woodlands, which experience dry, hot summers and mild winters with a moderate level of rainfall.
It's not especially colorful or diverse compared to forests and savannas, but it's mild and pleasant enough that humans have ironically become the biome's most obtrusive inhabitants, driving out (or at least thinning out) many of the native species such as hares, foxes, coyotes, and cougars. It is, for lack of a better term, a low-maintenance biome that provides some natural ambiance and agricultural potential - things that bona fide deserts fail to provide - without the drawbacks of more verdant climates (e.g., wood rot, animals getting into food stores, the health detriments of cold dampness, lots of bugs, etc). So we can say this is Earth nature's mediocrity - its comfortable middle ground where nothing is especially profound or complicated.
Toward the forested end of the spectrum, Mediterranean vegetation tends toward trees that can handle a more measured amount of rainfall, such as eucalyptus - but also hardier versions of more commonplace trees and woody bushes. Toward the semi-arid end, plants become smaller, generally more drab, and more prickly to avoid being eaten. The mammals are represented by rodents and a few, relatively small predators (excepting cougars) competing with birds-of-prey and rattlesnakes for some of the same food. Views:
The steppe is a more or less flat, semi-arid continental environment that is actually a type of savanna, but is typified by highland plains with grasses and shrubs. Unlike savanna in general, steppe is treeless, can be cold, and errs on the side of desert rather than wetland. There is not much to see on a steppe, although large herbivores may migrate through it, along with rodents, birds-of-prey, carrion eaters, and small predators.
Deserts and xeric shrublands are a distinct family of biomes characterized by increasingly severe lack of water in the environment. At the more benign end of the spectrum, there is complete overlap with Mediterranean and savanna, and the plant life transitions smoothly from those categories into committed desert vegetation (e.g., succulents). At the furthest extreme, there is no appreciable plant or animal life, but only a few oases that cling to survival amid virtual moonscape.
We have now come full circle, from the frigid desert wastelands of the poles to the dunefield infernos of the subtropics - from hell to hell - and along the way traveled through a multitude of paradises and a few muddled purgatories. We have seen an infinitesimal fragment of the lifeforms that cascade across the face of this world, and all in a razor-thin span of the surface of a single planet in one solar system.
So now I would like to show you something that illustrates beyond the power of words exactly what life is - what we all are, and indeed what we together become. As you watch the below video of a flock of birds, and see its tendrils reaching out and recombining, reach out your own arm and realize that the same thing is happening in you. I recommend going to full screen:
