What conditions on the young Earth would be necessary for the formation and continuance of life? The presence of water would be an obvious one. The Earth’s surface environment, recorded in geologic formations over the approximately 4 billion years, appears to have been maintained within a relatively narrow range in which liquid water was stable. Though the sun was so dim billions of years ago that the young planet should have frozen, it remain largely covered with liquid water because the early Earth was dominated by oceans, which lacked plants and algae—once considered to be plants. Moreover, the extant continents were much smaller, which increased the area of darker water and thus resulted in a lower planetary albedo effect. (The “albedo effect” is the electromagnetic radiation reflected back into space by the white surface of a growing ice sheet; albedo is Late Latin for whiteness, from the Latin albus, white.) Consequently, the absorption of a higher fraction of the incoming solar radiation, in combination with only slightly higher concentrations of greenhouse gases, probably carbon dioxide and methane, provided the Earth with a mild climate. In short, environmental niches in which life first emerged and later evolved on the Earth have undergone dramatic changes in response to evolving tectonic/geochemical cycles, biophysical events, as well as increases in the sun’s luminosity of about 25 to 30 percent over the Earth’s history.1
Another requirement for the occurrence and continuation of life on planet Earth was the generation of a large-scale magnetic field strong enough to protect Earth and its emerging life from the full force of the solar wind and its stream of charged particles—intense x-rays and high-energy ultraviolet emissions ejected from the upper atmosphere of the sun. A torrent of these particles from the young sun would have irradiated early life, as well as degraded the upper atmosphere and stripped away the water reserves, like it did to the upper atmosphere and water on both Venus and Mars over the ages.
In the year 1859, however, Irish chemist, Sir John Tyndall (August 2, 1820–December 4, 1893), discovered that carbon dioxide absorbs infrared energy in Earth’s atmosphere. Tyndall’s work built on that of Jean Baptiste Joseph Fourier (21 March 21, 1768–May 16, 1830), a French mathematician and physicist, who postulated that Earth’s surface temperature is a balance between energy from the Sun (“light rays” striking earth) and that emitted by Earth (“dark rays” reflected back into space, which are today increasingly intercepted and trapped by atmospheric carbon dioxide). Fourier is also generally credited with the discovery of the atmospheric “greenhouse effect.” It was, however, Tyndall who discovered that this balance is determined by the composition of the atmosphere, notably the concentration of carbon dioxide and aqueous vapor. The quantitative relationship between the concentration of carbon dioxide and its infrared absorption is now well established.2 But, this relationship depends on the Earth’s protective, magnetic field.
OUR MAGNETIC SHIELD
Earth’s magnetic field is generated by the swishing of molten iron deep in the planet’s outer core, where the motion caused a slight deflection, or curvature, in the molten iron, the “coriolis effect,” which helps to create a pattern in the movement of molecules. This perpetual movement leads to the formation of the “geodynamo” (literally, Earth generator), wherein the self-sustaining, physical motion of the molecules in the fluid of Earth’s out core is converted into magnetic energy.
Earth’s magnetic field, which emerged from its core about 3.45 to 3.5 billion years ago (just a billion or so years after the planet formed), was not yet strong enough to shield life from the sun’s deadly rays. During Archaean Era, from 3.8 to 2.5 billion years ago, the boundary in space, where the magnetic field meets the solar wind, was about 18,641 miles or less from Earth. Today, however, the “stand-off” boundary (termed “magnetopause”) between the magnetic field and the high-energy winds from the sun is 37,282 miles into outer space on the sunward side of Earth and much further on the other side. Although life as we know it depends on the relative stability of this border, it can shift in response to extreme energetic outbursts from the sun. (Archaea, from early Greek for “ancient things,” is the period when life first appeared on Earth, roughly 3.5 billion years ago, at which time it consisted of bacterial life forms and persisted thus for more than one billion years.)
How do we know this? By analyzing volcanic rocks from the Kaapvaal Craton (a region near the southern tip of Africa, which hosts the relatively pristine, early Archean crust), scientists found that some of the rocks were magnetized 3.45 billion years ago, which roughly coincides with the direct evidence of the first life on Earth, about 3.5 billion years ago. When these rocks solidified, a number of infinitesimal bits of iron-containing magnetite—embedded as inclusions in tiny crystals of quartz inside the molten rock—aligned themselves with Earth’s magnetic field, thereby acting like recording devices, which captured the strength and configuration of the ancient magnetic field. Although the rocks themselves had undergone some chemical changes throughout the eons, the quartz acted as the perfect, protective capsule for the magnetite.3
THE CHEMISTRY OF LIFE
The chemistry of life is the chemistry of reduced organic compounds, which makes the discovery of the worldwide, deep-sea, hydrothermal-vent systems profoundly important because of the way it informs our view the geological, geochemical, and ecological history of the Earth. (Hydrothermal is from the Greek hydr “water” + thermos “hot”) If we could go back in time and visit primordial Earth, we would likely find an active system of hydrothermal vents in areas where the sea floor is spreading because they probably arose as soon as liquid water accumulated on the Earth, more than 4.2 billion years ago.
Hydrothermal vents are volcanic areas, where seawater seeps into small cracks, which can penetrate a mile or more deep into the Earth’s crust, such as the hydrothermal vent three miles below the surface in a deep-sea canyon called the “Cayman Trough.” There, temperatures can reach 750 degrees Fahrenheit, which makes the water hot enough to melt lead. As a result, scalding, mineral-rich fluid is expelled from a geyser on the seafloor into the fridge, deep ocean, creating a smoke-like effect, which leaves behind towering chimneys of multicolored, mineral deposits and thick collections of fluorescent-blue microorganisms thriving in the slightly cooler waters around the chimneys. The amazing pressure—500 times stronger than the Earth’s atmosphere—keeps the water from boiling.
Although the basis of this ecosystem is chemical-eating bacteria, which use the hydrogen sulphide and methane erupting from the vents as food, there are also lush colonies of such organisms as blind shrimp, giant white crabs, and large red-lipped tubeworms that seem to lack a digestive system.
Because these under-sea vents are sources of numerous elements and organic compounds, which are transferred into the seawater, they can support life without oxygen or photosynthesis. (Photosynthesis is the process by which green plants convert incident light to chemical energy and synthesize organic compounds from inorganic compounds, especially carbohydrates from carbon dioxide and water, with the simultaneous release of oxygen.)
Instead, the microorganisms supported by these hydrothermal vents are termed “chemolithoautotrophs,” from the Greek chemikos, (“of or pertaining to juices”), lithos (“rock”), auto (“self”), and trophos (“one who feeds.”) Thus, chemolithoautotrophs, which belong to the domain of Bacteria, are literally “eaters of rock,” from which they use inorganic molecules as their source of energy. As such, they are critical in the biogeochemical (= biological + geological + chemical) cycling of many important elements, such as sulfur and potassium, which ultimately become nutritional constituents for more complex forms of life once released from the bedrock of which they were a part.4 Moreover, geochemical data reveal novel microbial processes, such as the formation of ethane and propane, which were previously assumed to be thermochemical (from the Greek thermos, “hot” + chemical) reactions of fossilized organic material.5 Today, these submarine hydrothermal vents are geochemically reactive habitats that harbor rich, microbial communities. As well, the seabed is a diverse environment that ranges from the desert-like areas of the deep seafloor to the rich oases that are present at seeps, vents, and the deposition of food islands, such as a dead whale or waterlogged, sunken tree.6
THE ATOMIC INTERCHANGE
“Nothing is wasted in our seas; every particle is used over and over again, first by one creature, then by another. In the spring, our ocean waters are deeply stirred and bring to the surface a rich supply of minerals ready for use by new life.”—Rachel Carson
Not surprisingly, the communities that arise when a whale dies, such as the female California gray whale, and sinks to the bottom of the ocean display underwater versions of the classical stages of succession and change seen in terrestrial ecosystems. But instead of grasses and forbs giving way to shrubs, which yield to trees that mature into a forest, dead whales first nourish such scavengers as hagfish, then bone-eating zombie worms, and eventually clams, which use inorganic chemicals for sustenance.
A California gray Whale washed up on an Oregon beach in the early 1970s.
In this first stage (which some researchers term the “mobile-scavenger stage”) a whale is largely intact, but has hundreds of hagfish feeding on it. These eel-shaped fish, each about sixteen inches long, use their sharp, rasping teeth to scrape bits of meat off the carcass. They also grip a whale with their mouths, tie themselves in a knot, and use their bodies to loosen chunks of flesh. In addition, Pacific sleeper sharks grab the whale and twist their whole bodies back and forth, back and forth, until they finally rip off a piece of flesh.
In all, some 38 species of scavengers have been observed in an open feast during this stage, and they do a good job, when you consider that a whale’s soft tissue accounts for approximately ninety percent of its weight. In fact, one whale, which weighed just over a ton (about 2,200 pounds), had the bulk of its flesh devoured in less than eighteen months.
A shark took a bite out of the whale.
The second or “enrichment opportunist stage” is composed of smaller organisms scavenging the “leftovers.” These secondary scavengers include snails, amphipods that look like shrimp, and segmented worms. Around one whale, which had been on the ocean bottom for almost two years, every 1.2 square yards of sediment hosted as many as 45,000 individuals, which says nothing about the microbes.
At times, huge-celled bacteria form long filamentous lines that appear to the naked eye as a pale bacterial mat, which looks like it had snowed. There is also a segmented worm, affectionately called “snowboarding worm,” that leaves a trail as it eats its way through the bacterial mat. In addition, many other segmented worms, called “polychaetes” (polys = Greek for “many” + chaet = New Latin for “bristle”), show up during this second stage. Although related to earthworms, those species that congregate around whale carcasses are much more diverse than their terrestrial cousins.
Finally, there are bone-eating “zombie worms,” which get their nutrition by sending a tangle of green, root-like coils into the whales bones. Inside of this green tangle reside rod-shaped bacteria that break down the complex, organic compounds of which the whale’s skeleton is composed.
When the hordes of wee creatures have reduced the whale to nothing but a pile of bones, the third stage begins, which is termed the “chemoautotrophic stage.” Many of the larger organisms that comprise this stage carry their own sulfide-metabolizing bacteria, such as the vesicomyid clams (vesicoz, which is Latin for “bladder” + mydos, which is the Greek word for “decay”). These clams don’t eat in the usual sense, but rather get their nutriments from sulfide-metabolizing bacteria that live in their gills. There is also a species of mussel that can amass a population of more than 10,000 individuals on the skeleton of a single whale, in addition to which there is a species of polychaete worm, which forms such dense colonies around whale skeletons they resemble lawns of “orange grass.”
The fourth and final stage is called the “reef stage,” because, with the nutritional component exhausted, the community shifts to undersea animals that require craggy structures as habitat. At this point, a whale’s skeleton acts much like anchorage.
The carcass of a whale settling to the ocean bottom offers as much food as would normally be delivered by the regular rain of detritus in 2,000 years. Moreover, some whale carcasses in the third stage are still bristling with chemoautotrophs after seventy to eighty years of resting on the deep-ocean floor.7
A whale that dies and sinks to the ocean floor is therefore critical to the long-term structural and functional health of the bottom-dwelling organisms, and so the ocean. The ocean, in turn, is an interactive, organic whole defined not by its respective parts, but rather by the interdependent functional relationships of those parts in creating the whole—the intrinsic value of each piece and its complimentary function. The sunken body of a dead whale slowly decomposing for nearly a century, while it enriches the deep ocean is part of Nature’s rollover accounting system in that re-investments of biological capital in the Nature’s health plan are mediated, as it were, through the atomic interchange.
And yet, even today, the deep oceans of the world remain mysterious and little known. For example, deep seas include some of the most extreme ecosystem conditions on Earth, such as the deep hypersaline basins of the Mediterranean; these super salty, acidic, sulfurous, and permanently oxygen-starved (anoxic) basins lie in the deep waters of the Mediterranean. These permanently anoxic systems are inhabited by a huge, largely unexplored diversity of microbial life.
Although several single-celled organisms can live under permanently anoxic conditions, and a few multi-celled organisms can survive temporarily in the absence of oxygen, it has heretofore been accepted that multi-cellular organisms cannot spend their entire life cycles in the absence of free oxygen. However, three new genera of minute, multi-cellular animals, which have been placed in their own phylum (Loricsifera), have been found living in the sediments of the deep, anoxic, hypersaline L’Atalante basin of the Mediterranean. These organisms provided the first evidence that multi-cellular life can exist throughout its entire life cycle in deep-ocean sediments that are permanently devoid of molecular oxygen. They appear to succeed through an obligatory anaerobic metabolism (one free of oxygen), in much the same manner as single-celled organisms do.8 Nevertheless, whether we understand it or not, whether we accept it or not, “the evolution of Earth’s atmosphere is linked tightly to the evolution of its biota.”9
Series on Biodiversity:
1. (1) Minik T. Rosing, Dennis K. Bird, Norman H. Sleep, and Christian J. Bjerrum. No Climate Paradox Under the Faint Early Sun. Nature, 464 (2010):744-747 and (2) Sid Perkins. Dark Ocean Kept Early Earth Warm Under A Faint Sun. Science News, 177 (2010):11.
2. (1) Elisabeth Crawford. (1997) Arrhenius’ 1896 Model of the Greenhouse Effect In Context. Ambio, 26 (1997):6-11; (2) Jean Baptiste Joseph Fourier. http://en.wikipedia.org/wiki/Joseph_Fourier (accessed on June 28, 2010); and (3) Sir John Tyndall. A short Biography. http://www.igp-web.com/carlow/John_Tyndall.htm (accessed on June 28, 2010).
3. The foregoing discussion of the Earth’s magnetic field is based on: (1) Moira Jardine. Sunscreen for the Young Earth. Science, 327 (2010):1206–1207; (2) John A. Tarduno, Rory D. Cottrell, Michael K. Watkeys, and others. Geodynamo, Solar Wind, and Magnetopause 3.4 to 3.45 Billion Years Ago. Science, 327 (2010):1238–1240; (3) John Matson. Shields Up: Magnetized Rocks Push Back Origin Of Earth’s Magnetic Field Earth’s Churning Interior Produced A Protective Magnetic Field As Early As 3.45 Billion Years Ago, Closer To When Life Began. Scientific American. http://www.scientificamerican.com/article.cfm?id=geodynamo-start-up (accessed on March 29, 2010); (4) James Dacey. Earth’s Magnetic Field Older Than We Thought. Physics World http://physicsworld.com/cws/article/news/41929 (accessed on March 29, 2010); (5) Lisa Grossman. Shields Were Up On Early Earth. Science News, 177 (2010):12; and (6) Introduction to the Archaean. http://www.ucmp.berkeley.edu/precambrian/archaean.html (accessed on March 29, 2010).
4. The preceding discussion of the of hydrothermal vents is based on: (1) William Martin, John Baross, Deborah Kelley, and others. Hydrothermal Vents and the Origin of Life. Nature Reviews Microbiology, 6, (2008):805-814; (2) Hydrothermal Vents http://www.ceoe.udel.edu/deepsea/level-2/geology/vents.html (accessed on April 13, 2010) and (3) http://en.wikipedia.org/wiki/Hydrothermal_vent (accessed on April 13, 2010; and (4) http://abcnews.go.com/International/wireStory?id=10350645 (accessed on April 13, 2010).
5. Kai-Uwe Hinrichs, John M. Hayes, Wolfgang Bach, and others. Biological Formation Of Ethane And Propane In The Deep Marine Subsurface. Proceedings of the National Academy of Sciences USA, 103, (2006):14684–14689.
6. (1) Chris Maser and James R. Sedell. From the Forest to the Sea: The Ecology of Wood in Streams, Rivers, Estuaries, and Oceans. 1994. St. Lucie Press, Delray Beach, FL. 200 pp.; (2) G. W. Rouse, S. K. Goffredi, and R. C. Vrijenhoek, “Osedax: Bone-Eating Marine Worms with Dwarf Males,” Science 305 (2004): 668–671; (3) T. G. Dahlgren, A. G. Glover, A. Baco, and C. R. Smith, “Fauna of Whale Falls: Systematics and Ecology of Anew Polychaete (Annelida: Chrysopetalidae) from the deep Pacific Ocean,” Deep Sea Research Part I: Oceanographic Research Papers 51 (2004): 1873–1887; (4) Susan Milius, “Decades of Dinner: Underwater Community Begins with the Remains of a Whale,” Science News 167 (2005): 298–300; and (5) Bo Barker Jørgensen and Antje Boetius. Feast and famine—microbial life in the deep-sea bed. Nature Reviews Microbiology 5 (2007):770-781.
7. The foregoing discussion is based on: Susan Milius. 2005. Decades of Dinner: Underwater Community Begins with the Remains of a Whale. Science News 167:298-300.
8. Roberto Danovaro, Antonio Dell’Anno, Antonio Pusceddu, and others. The First Metazoa Living In Permanently Anoxic Conditions. BMC Biology, 2010, http://www.biomedcentral.com/1741-7007/8/30 (accessed on July 1,2010).
9. James F. Kasting. The Rise of Atmospheric Oxygen. Science 293 (2001): 819-820.
Text and Photos © by Chris Maser 2012. All rights reserved.