Some Ideas Regarding the Biological Colonization of The …

1. INTRODUCTION

Far from being a purely theoretical science, Biology has many practical applications. This science will have a huge importance for the future of humanity. What can Biology bring to mankind? There are three main answers:

Health Biological sciences will play an important role in fighting various infectious agents (viruses, bacteria), in curing other diseases (cancer, for example) and in "repairing" wounded tissues, thus increasing peoples life expectancy.

Food Considering the rapid demographic growth, the traditional food sources will become insufficient for feeding Earths population. Biologists will have the duty to search for organisms that are more nourishing and easier to be cultivated (algae, crustaceans etc.), and also to improve the species already cultivated, in order to increase their productivity, their nutritiousness and their resistance to pests.

Space While the human demographical growth is unlimited, our planets resources are limited. Mankind will have to conquer and colonize the extraterrestrial space. We know that none of the planets in our Solar System has the natural conditions necessary to human colonization. The solution is to modify these conditions and to gradually implant terrestrial life forms on these planets, in order to create habitats for the future colonists.

This essay is regarding the latter subject.

The idea of implanting terrestrial life on other planets (a process called

This essay will treat the case of planet Mars, the closest, from all points of view, to Earth. Also, it will focus mostly on the biological aspects of terraformation.

2. MARS: PREMISES FOR TERRAFORMATION

A. Natural conditions

Mars belongs to the group of the luric planets, together with Mercury, Venus and Earth. From all the planets of the Solar System, it is situated at the shortest distance from Earth. Its diameter is slightly larger than half of our planets diameter. Its orbit is exterior to Earths orbit. The rotation period is of 24 hours and 40 minutes (a martian day is almost equal to a terrestrial one) and the duration of the revolution movement (the martian year) is 687 days. Mars has seasons, like our planet. Because the distance from the Sun is longer, Mars receives only 43% of the sunlight that reaches Earth. The gravitational force is 38% of the terrestrial one. The planet has no magnetic field and no tectonic activity. There is, instead, some volcanic activity.

The atmosphere is extremely rarefied, having a pressure of only 7.4-10

The average temperature is about -60C, but temperatures can vary between -75C and +25C, according to the latitude and season. By comparison, the average temperature on Earth is about +15C.

The quantity of ultraviolet radiations that reaches the surface of Mars is much larger than on Earth, being deadly for almost any life form.

The relief forms are inequaly distributed on the surface of the planet. The southern hemisphere has high altitudes, with many impact craters, volcanic mountains and three large depresions: Hellas, Argyre and Isidis (probably huge craters). The northern hemisphere has, predominantly, low altitudes. There are two polar caps composed of frozen water and carbon dioxide. There is no liquid water on the planets surface.

The upper layer of the martian crust, a few kilometers thick, is called regolith and is composed of rocks, dust and ice. It is, probably, porous (due to the low gravity). The entire planets surface is covered with a red dust.

The samples taken by the Mars Pathfinder mission from the surface, together with the analyses of several meteorites, of martian origin, show the following chemical composition:

Probably, the analyses must be redone for K2O and MnO2. This composition is similar to that of the terrestrial rocks, except for the iron compounds, much more abundant on Mars. In the primary rocks iron is found in its reduced form (Fe2+), and in the soil, in its oxidized form (Fe3+). The predominant minerals at the surface are haematite (Fe2O3), jarosite (KFe3(OH)6(SO4)2), goethite (FeO(OH)). It seems that the upper layer of the regolith contains oxidizing agents.

Apparently, the environmental conditions on Mars are improper to any living organisms. However, there are more and more evidence that indicate these conditions were not always the same. Most scientists think that, in the past, there was liquid water on Mars and, obviously, the temperatures were higher and the atmosphere was denser. This poses a problem: where and why most of the martian atmosphere disappeared? There are two theories. One of them says that the planet lost its atmosphere due to violent impacts with other celestial bodies (comets, asteroids). In this case the atmospheric gases were lost in space and trying to recompose the martian atmosphere would be almost impossible with our current technical means. The second theory says that the atmosphere was slowly eroded, during geological eras, by the solar wind, after the volcanic activity slowed down, causing the atmospheric gases to stop recycling. This way, most of the gases would have infiltrated, under various forms, into the martian crust. If this theory is true, there is a big chance that the planets atmosphere could be modified, allowing the implantation of life on Mars.

B. Resources for terraformation

Planet Mars has, under various forms, all the chemical elements necessary to life.

Water

The most obvious water reserves on Mars are located in the polar caps. According to some estimations, these contain around 5,000 km3 of water (equivalent to a 4 cm layer on the entire planets surface).

It seems that other water reserves exist in some stratified deposits (alternate layers of dust and ice) in the territories around the caps.

Apparently, there are, in the regolith, in the regions situated north and south of 40 latitude (North and, respectively, South), ice lenses (somehow similar to the terrestrial permafrost).

Squires and Carr (1986) estimated the total water quantity in the caps and regolith to the equivalent of a 13-100 m thick layer of liquid water on the entire planet.

Also, liquid water is supposed to exist in the lithosphere. Wittome says that the regolith, due to its porous structure, allowed water to infiltrate. This means that in the regions situated at more than 40 latitude, at a few kilometers depth, there sholud be thermal waters, at very high pressures. A recent model of the hydrological cycle on Mars (Clifford, 1993), shows that in the lower areas of the planet, there could be subterranean waters, at artesian pressures. Also, some minerals should contain water.

Carbon

It is known that the polar caps contain solid carbon dioxide. Some of this sublimates during the martian summer and solidifies in the winter, causing variations of the caps area. Initially, it was thought that most of the southern cap was made of CO2 (estimated to the equivalent of 10-100 mbar of gaseous CO2). However, recent data show that this cap is composed mostly of water.

Also, it is estimated that the regolith contains large amounts of CO2. Zent et al. mentioned the equivalent of 30-40 mbar, while other estimations indicate as much as 300 mbar. Some chemical tests showed that the martian regolith is capable of absorbing large quantities of CO2.

On Mars, carbon is also found in carbonates (of calcium, iron, magnesium etc.). It was observed the existence of layered deposits (calcium carbonate sediments). It is supposed that these are located in former lakes and evaporation basins. Such deposits were also discovered in Valles Marineris (a huge canyon system). Based on the low value of the Ca/Si ratio in the regolith, Warren (1987) says that there are large amounts of CaCO3 on Mars (there is only a little calcium in the regolith because most of it is concentrated in carbonates). According to some estimations, the carbonate reserves should contain the equivalent of 30 mbar of gaseous CO2. The presence of CO2 is extremely important for modifying the environmental conditions on Mars, as it will be shown below.

Nitrogen

Nitrogen is a vital element for every organism, being an important part of the composition of proteins, nucleic acids and other organic substances. The quantity of this element on Mars is unknown. This poses a big problem to those interested in the possibility of terraforming the planet. The atmospheric dinitrogen quantity is very small (2.7% of the atmosphere). Still it is preconized the existence of substantial amounts of nitrates in the regolith (according to some estimations, the equivalent of 300 mbar of gaseous N2), in former evaporation basins from the equatorial regions, together with the presence of underground ammonia deposits. Analyses done on martian basaltic meteorites show that these contain an amuont of nitrates and phosphates larger than the terrestrial basaltic rocks (scientists tried the experimental cultivation of some plants on soils containing martian meteoritic rocks, with spectacular results). Generally, it is accepted that there are important nitrate reserves on Mars, but their quantity is unknown.

Organic matter

Some specialists think there are some organic material deposits located at 3-40 meters below the planets surface (Bullock et al., 1994) or in the polar zones (Bada and McDonald, 1995).

In space, large amounts of organic compounds (especially hydrocarbons) are found in celestial bodies called carbonaceous chondrites (meteorites, asteroids, satellites). Still, it appears that on the planets surface there are no organic substances. This fact is probably due to the strong oxidizing agents in the upper layer of the regolith, that quickly oxidized the hydrocarbons, forming CO2. That is why, if there really is organic material on Mars, it should be found buried in the regolith. Also, the two natural satellites of the planet, Phobos and Deimos, belong to the carbonaceous chondrite class.

Recently, the Mars Express probe discovered some methane emissions of unknown origin.

Other elements

According to spectrometric analyses, sulphur is found in the martian "soil" in 10-100 times higher concentrations than on Earth. It is found in the form of sulphates (like jarosite), extremelly abundant on Mars. On Earth, large reserves of sulphur compounds are associated with volcanic activity.

Spectrometric analyses for phosphorus could not be effectuated, but it is thought that this is abundant, as the composition of martian meteorites show.

Other elements, like iron, manganese, potassium etc., exist in large quantities on Mars.

Additional chemical and mineralogical analyses are needed in order to know the exact quantities and locations of the various substances necessary to ecopoiesis.

C. Conditions necessary to life

To the proper going of metabolic activities of terrestrial organisms, envinronmental temperatures higher than 0C are required, although there are organisms that can resist for a long time at negative temperatures. It is known that during the martian summer, in the equatorial regions, temperatures can grow up to +25C, but this is not enough.

Generally the atmospreric pressure should be higher than 10 mbar, although some plants and anaerobic bacteria can withstand pressures below one millibar. The partial pressure of CO2 must exceed 0.15 mbar (on Mars, it is much higher than this limit). O2 partial pressure must be higher than 1 mbar. Many anaerobic and even aerobic microorganisms can grow in pure CO2 atmospheres. Some cyanobacteria and algae like Cyanidium sp. or Scenedesmus sp. produce, by photosynthesis, the oxygen needed for their respiration and, in the dark periods, they become anaerobic (Seckbach, 1970). It was found out that in the cyanobacterial and algal colonies grown at high CO2 concentrations will appear mutants that require larger and larger concentrations of this gas (Spalding et al., 1983; Marcus et al., 1986). This way mutants could be selectionated for colonizing Mars. Plants need, for photosynthesis, 20-210 mbar of O2 (mythochondrial enzymes need oxygen) but can be adapted to as little as la 0.1 mbar. Nitrogen fixing bacteria can begin their activity at 5-10 mbar of N2. The solar light that received by Mars is more than sufficient for photosynthesis.

For humans, requirements are much higher. The atmosphere must have a mass three times larger than the terrestrial one, in order to compensate the low gravity. The atmospheric pressure must exceed 500 mbar (on Earth it is around 1,013 mbar, at the sea level). CO2 partial pressure needs to be below 10 mbar (otherwise, it becomes toxic). O2 pressure must be between 130 and 300 mbar (too little oxygen causes hypoxia, too much, causes combustion). Additionally 300 mbar of buffer-gas are needed. This is necessary to prevent combustion, due to the presence of O2 in the atmosphere. The ideal buffer-gas is N2 (on Earth, it constitutes more than three quarters of the atmosphere), but, between certain limits, it can be replaced by He, Ar, Ne, Kr,Xe, CH4, H2O, CO, HCN, SF6.

3. ECOPOIESIS

The terraformation of a planet has two stages. The first stage was called by specialists ecopoiesis or ecosynthesis and its finality is the implantation of the first life forms on the planet and the creation of self-regulating anaerobic ecosystems. The second stage is the true terraformation and consists of creating an aerobic biosphere that will allow humans to colonize the planet.

As shown above, the main factors that prevent life implantation on Mars are too low atmospheric pressure, too low temperatures, lack of a protection against ultraviolet radiation, lack of liquid water on the planets surface. For all these problems there is only one solution: greenhouse effect.

The greenhouse effect is based on the property of certain gases (called greenhouse gases) to retain the solar heat reflected by the planets surface. The solar radiation directly heats the surface. Without greenhouse gases, a large part of the resulting heat would be lost in space. The greenhouse gases absorb it, heat the atmosphere, the atmosphere heats furthermore the planetary crust and the cycle goes on.

The best-known greenhouse gas is CO2. This constitutes most of the martian atmosphere, but it is insuficient because of the low atmospheric pressure (although it appears that, indeed, Mars is going through a warming process). Still, as shown above, CO2 is, probably, quite abundant on Mars, either as carbonic ice or as carbonate deposits.

Ecopoiesis on Mars could be realized by a human mechanical intervention that would produce a chain reaction. An artificial heating would release CO2, that, through the greenhouse effect, would release other quantities of CO2, H2O (water vapor is a greenhouse gas), maybe NH3 etc.

Several mathematical models of a greenhouse effect on Mars were done. One of them, created by McKay et al., show that an artificial temperature growth of only 4C could sustain a chain reaction, causing the southern polar cap to completely melt down (an initial 25C impulse would be needed). The release of 800 mbar CO2 in the atmosphere would bring the average temperature on the planet to 250 K (-25C), compared to the actual 213 K (-60C). Releasing 2 bar CO2 would increase the temperature to 273 K (0C), and 3 bar CO2, to 280 K. The last estimations of the southern caps composition infirm the presence of such large amounts of CO2, but the model remains valid. The sublimation of the CO2 from the polar caps would be followed by the release of this gas from the regolith (where CO2 is more abundent than in the caps). An additional 10C increase is required (Zubrin, McKay), producing a chain reaction. Other amounts of CO2 can be released from the carbonate reserves, using more aggressive methods, as shown below.

Even if McKays previsions would prove to be too optimistic, temperatures on Mars would still increase enough to allow the colonization of terrestrial organisms. The presence, in the atmpsphere, of several hundred millibars of CO2 would have many effects. First, the total atmospheric pressure would increase to acceptable values. Then, the atmospheric temperature would increase, allowing the existence (temporary or even permanent) of liquid water, at least in the equatorial regions. Finally, an ozone layer would appear and it would absorb most of the deadly radiations that reach the surface. In the upper layers of the atmosphere, under the action of ultraviolet radiation, carbon dioxide, goes through a simple splitting reaction, producing ozone.

Linda and James Graham show that all that life needs in order to be implanted on Mars is 90-300 mbar CO2 and 2 mbar O3 (for protection against radiation). These objectives are perfectly realizable.

If the theory of ecopoiesis, shown above, is rather simple, its practical realization is more problematic. Several solutions were proposed:

A. Orbital mirrors

The artificial heating of the polar caps and of the regolith could be done by placing large mirrors on the planets orbit. These would reflect the sunlight towards certain areas on the planet (especially the southern cap), triggering the greenhouse effect.

A mirror with a diameter of 20 meters was already placed in orbit around Earth in the 1980s (the "Znamia" project) in order to illuminate Russias northern territories during the polar night. It is preconized the launch, in the next future, of a mirror of 200 meters in diameter, with the same purpose. Most of the specialists say that a mirror that would heat enough the southern cap must have at least 125 kilometers in diameter (and a mass of about 200,000 tons). It would be built of aluminized mylar. The technology for building it is known, being the same as for producing the "solar sails" (that, in the future, will be used for the propulsion of spaceships). Its ideal location would be a stationary one, at the equilibrium point between the solar winds force and the planets gravitation.

Building such a mirror is not such a big problem (it would be the equivalent of Earths aluminium production for five days) but transporting it to the martian orbit is. Perhaps it should be built of small modules or replaced with many small mirrors. Using simultaneously more heating methods would greatly reduce the mirror's necessary dimensions.

B. Nuclear explosions

Using nuclear weapons to release carbon dioxide seems to be a easier solution for our current technological possibilities. Also, this would, finally, give Earths huge atomic arsenals a real utility for mankind.

Nuclear warheads could be used in two ways. First, they could be detonated at the planets surface, in the polar zones, in order to melt the caps. According to some estimations, it would be sufficient if, during four martian years (about seven terrestrial years), at the beginning of each martian spring, a nuclear warhead of 20 kilotons (thus, not a very powerful one) would be detonated in a dusty area near the southern cap, for the entire cap to melt. This would cumulate the direct effects of the explosions heat with the creation of dust storms that would cover the cap, reducing its albedo (this aspect will be discussed below). Probably, these estimations are too optimistic, but the idea is valid.

Second, subterranean nuclear explosions could be used to release greenhouse gases (CO2 and water vapor) from the carbonate deposits and from the "permafrost". Detonating nuclear warheads in nitrate deposits would release N2 and O2.

This solution is criticized for two main aspects. The first is the quantity of radiations that would appear after the explosions and that would make vast regions of the planet inhospitable to life. Yet, there are many ways of reducing the radioactive contamination. Using thermonuclear warheads (based on hydrogen fusion), that produce less radiations than fission weapons and detonating them, mostly, underground, would limit the afffected area. Also, it sould be considered the fact that terraformation would be a long process that will take, probably, tens of thousands of years. In this time, radioactivity would be greatly reduced, so that the future human colonists would not be affected. The second aspect, more problematic, is the number of nuclear warheads needed, which, according to some estimations, would be to big compared to the available atomic weapons.

C. Greenhouse gas production

Another solution is the artificial enrichment of the martian atmosphere in greenhouse gases. There are greenhouse gases much more efficient than carbon dioxide: halocarbons, ammonia, methane. Releasing these in the atmosphere in sufficient quantities would heat the planet and would sublimate the carbon dioxide, triggering the chain reaction necessary to ecopoiesis.

Halocarbons

Chlorofluorocarbons (CFC), responsible of destroying the ozone layer on Earth, are extremely strong greenhouse gases. It is estimated that a very small concentration of CFC, of one part in a million, would be enough to heat the atmosphere with 60C.

Yet, they are useless on Mars, for two reasons. First, they would destroy the ozone layer, the only defense against radiations. Second, ultraviolet radiations photolise CFC. The life of CFC would be very short (estimations indicate something between a few days and several tens of years) and they should be produced continously.

Releasing these gases in the martian atmosphere would mean their production in situ and, thus, the existence on Mars of the necessary industrial instalations. The main problem is finding raw materials. Fluorine can be extracted from minerals like apatite and fluorite and then, in reaction with atmospheric CO2 would form PFC. It was calculated that, in order to release a quantity of halocarbons sufficient for raising the temperature by 5C, an energy of around 1,315 MW is needed, equal to that produced by an ordinary nuclear power plant (Zubrin, McKay).

Ammonia

Ammonia is a strong greenhouse gas. It is unlikely that it could be produced, in short time and in sufficient quantities, on Mars. It could be "imported" from other regions of the Solar System. Comets and some asteroids contain large amounts of ammonia.

Deviating these celestial bodies towards Mars would be a problem. Although not far from the planets orbit there is a large asteroid belt, it would be easier that asteroids containing NH3 to be brought from the regions beyond Pluto, because their revolution speed is lower and they are easier to deviate. Some of the ammonia that they contain could be used for propulsion. It was calculated that for transporting an asteroid of 10 billion tons (2.6 kilometers in diameter) constituted entirely of NH3 and situated at a distance of 12 astronomical units, four 5,000 MW thermonuclear propellers (tested since the 1960s) would be enough. These would heat the asteroid, sublimating 8% of the ammonia quantity and using it for propulsion.

The transport would take ten years and would increase the temperature on Mars by 3C. In order to avoid causing great damage to the planet, the asteroid should not be crashed directly into the planets surface, but aerobraked.

Yet, the practical realisation of such transports would be quite difficult at the current technological level. Also, it is extermely improbable that an asteroid would be formed entirely of ammonia. Known asteroids and comets do not contain more than 10% ammonia.

Methane

Methane can be, in theory, "imported" from the Solar System, just like ammonia.

Finding a hydrogen source for this reaction would be problematic.

D. Using thermal waters

As shown above, the martian regolith is porous, due to the low gravitational force and, thus, permeable to water. This caused liquid water (which in the past was, probably, abundant on Mars) to infiltrate at various depths in the planets crust. Water temperature and pressure are high at great depths. Wittome says that at 6 km depth there should be water reserves at 300C. Also, colder water should exist at one kilometer depths, in the regions beyond 40 of latitude, especially in the Tharsis zone and, maybe, in Valles Marineris. If Cliffords model was correct, the lowlands (mostly in the northern hemisphere) could have accesible subterranean waters.

In order to exploit these water reserves, drilling is required. Thermal waters could be used in many ways. They could be transported by pipelines to the ice deposits in the regolith contributing to their melting and releasing CO2. Acidified thermal waters could be used for dissolving carbonate deposits, forming CO2, and nitrate deposits, forming N2 and O2.

Due to its enormous pressure, water could be let to flush in the atmosphere, vaporizing itself (because of its high temperature and low atmospheric pressure) and coming back at the surface as snow. Due to impurities contained by subterranean water, this snow would have a darker colour and, if it falls on the polar caps, it would help reducing their albedo and melting them.

Thermal waters could be used for producing the electricity needed by other installations necessary to ecopoiesis (drills, PFC factories etc.).

Finally, if thermal waters were directed to the bottom of a crater or of a depression in the crust, a lake would appear. These lakes would be covered by an ice crust and, below it, liquid water. If such lakes were located in the equatorial regions, it would be possible that, during the summer, they would not be frozen. In these lakes, living organisms could be introduced, preparing them for the moment when the natural conditions at the surface would be suitable to life. There are cyanobacteria and unicellular algae that can grow and photosynthesize even under thin ice crusts. Various chemosynthesizing organisms could grow in these lakes. The existence of artificial thermal springs would favorize the growth of microorganisms, such as methanogen bacteria, that prefere this kind of habitats and that would produce methane, a strong greenhouse gas.

The main problem for exploiting thermal waters is that of transporting to Mars and keeping in function installations like drills, pipelines, power generators etc. There are quite many such devices needed for obtaining significant results. Knowing the exact location of the subterranean water reserves is also necessary.

E. Reducing the albedo

The word "albedo" means the amount of light reflected by a certain body. A low albedo means that the body absorbs more solar radiation and, thus, it heats more. The martian ice caps reflect much solar light. If their surface was covered with darker substances, their albedo would decrease and the ice would heat, allowing the carbon dioxide to sublimate.

The easiest way of doing so is by creating dust storms. As shown above, the planets surface is covered by a red dust (it is red because of the iron oxides). The red dust would cover areas of the polar caps, helping them to melt.

Furthermore, dust storms would have another importance for ecopoiesis. It was observed that the distribution of the small ozone quantity in the martian atmosphere varies with the season and latitude (Lindner, 1988). These variations can be as large as 40%. During the first stages of ecosynthesis, until a sufficiently thick ozone layer would be formed, these variations would let entire regions of the planet without protection against ultraviolet radiations. Dust storms, not only would help the chemical process of forming ozone, but would absorb themselves part of the radiations.

As shown above, reducing the albedo could also be done with the "dirty" snow produced by using thermal waters.

Another possibility would be reducing the general albedo of the planet. This way, Mars would absorb more solar radiations and the whole atmosphere would become warmer. This could be done by covering large areas of the martian surface with dark substances (such as hydrocarbons). As shown above, it is possible that, at various depths in the regolith, hydrocarbons would be found. However, locating and extracting them would pose big technical problems. Furthermore, their quantity is unknown and neither their lifespan in the oxidizing environment at the regoliths surface.

It would be more economical to use the planets natural satellites. These have relatively small dimensions (they are probably former asteroids) and belong to the carbonaceous chondrites class, containing ice and black rocks, rich in hydrocarbons. Temperature at their surface is around 313 K (40C). Phobos has 22 kilometers in diameter. Its revolution speed around the planet is very high. Its orbit is continously closening to the planet and, in the far future, it will crash into Mars. Deimos has only 12.6 kilometers in diameter and a much lower revolution speed. Deviating and disintegrating these satellites in the martian atmosphere, using powerful nuclear explosions, would cover large territories with dark organic material. The impact of large satellite fragments (that, as shown above, have a high temperature) with the planets surface would release certain amounts of CO2 from the regolith, ausing, this way, a slight global warming.

The resulting organic material could become food for heterotrophic microorganisms, either under this form, either as intermediary products resulted after their oxidation by the regolith (salts of the acetic, oxalic, benzenocarboxilic acids etc.).

Pure carbon (black) can be obtained by reacting carbon dioxide with hydrogen, using, as catalyzers, iron, rubidium etc.:

Again, the problem is finding a hydrogen source.

These would be the main solutions for modifying the natural conditions on Mars. Of course, many other ones were proposed. For example, building small human colonies (isolated from the environment) and developing industrial activities capable of realising ecopoiesis. These colonies would also have artificial biospheres where organisms could be prepared for colonizing the planet. However this would take a long time and would pose technical problems.

Another idea would be building satellites that would receive solar energy and send it to the polar caps under another form (laser, microwaves).

As one could observe, for each of the solutions shown above, the technical requirements are relatively large. They would be reduced by using more, or even all of these methods, simultaneously. This way, the orbital mirrors needed would be smaller, so as the number of the nuclear warheads, of the drilling installations, or the amount of artificially produced greenhouse gases.

When can ecopoiesis start? As soon as possible, strictly depending of the technical means. When it would be over? There are various estimations. Generally, it is thought that one hundred years, or even less, would be enough for the first anaerobic ecosystems to be installed on Mars. After introducing the first organisms, the global warming due to human intervention, would continue until the martian atmosphere would have an acceptable pressure and temperature for superior organisms, including humans.

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Some Ideas Regarding the Biological Colonization of The ...