Theosophy speaks of a meteoric veil surrounding the earth . The meteoric veil is said to be many scores of miles thick and to consist partly of dust rising up from the earth but mainly of interplanetary and interstellar dust – most of it very fine, but including larger bodies. The dust originates from disintegrated moons, planets, and stars.
The meteoric veil partly acts as a protective shield, screening earth, for example, from the terrific energy of the sun. In addition, solar energies reaching the earth arouse electromagnetic currents in this thick shell of meteoric dust. The electromagnetic interchanges between the earth and its meteoric veil help to produce various meteorological phenomena, including storms, lightning, precipitation, droughts, changes in temperature, and the auroras, and they also generate some 70% of the earth’s heat. The varying influx of cosmic dust is connected with the succession of glacial and warm periods, and associated expansions and contractions of the atmosphere.
Every globe of a planetary chain is surrounded by a meteoric veil during its active periods, or globe rounds. Mars (i.e. its visible globe D), which is currently in a state of dormancy or obscuration between its third and fourth rounds, has only a very thin shell of meteoric matter surrounding it because the forces of attraction holding the meteoric masses together have been relaxed. Mercury has a thicker meteoric veil around it, as it is currently coming out of obscuration to begin its seventh round, while Venus has an even denser veil surrounding it, being in its seventh round. Saturn’s rings are a thickening of its meteoric veil in the plane of its equator.
2. The KH letter
The earliest theosophical reference to the earth’s meteoric veil is found in a letter written by mahatma Kuthumi (KH), received by A.P. Sinnett in October 1882 . In it he writes: ‘Earth’s magnetic attraction of meteoric dust, and the direct influence of the latter upon the sudden changes of temperature especially in the matter of heat and cold, is not a settled question to the present day, I believe.’
Ranyard’s article begins by giving several examples of magnetic, metallic particles of probable meteoric origin being collected from basalt rock, snow and ice, the surface of tall buildings, deep-sea clays, and the atmosphere. Much of what KH’s letter says about contemporary scientific views and discoveries regarding meteoric dust is in fact taken from Ranyard’s article, as the following quotations show:
In 1876 Mr. John Murray published a paper ... in which he gave an account of his examination of the deposits found at the bottom of the oceans and seas visited by H.M.S. Challenger. In many of the deep sea clays Mr. Murray found numerous magnetic particles, some of which he extracted by means of a magnet carefully covered with paper. ... Mr. Murray concluded that the particles had a cosmic origin. ...
There can be little doubt that in the course of a year millions of meteors enter the Earth’s atmosphere. A few of the larger masses reach the Earth’s surface, but by far the greater number appear to be consumed in the higher atmosphere. The above observations show that minute particles of iron frequently reach the Earth’s surface without having undergone any change such as might be expected to result from their passage through the air in an incandescent state. ...
There can be little doubt that the air up to a great height above the Earth’s surface is impregnated with dust. ...
Much evidence has been collected ... which tends to show that many of the larger meteoric masses enter the Earth’s atmosphere with velocities which indicate that they are moving in hyperbolic orbits, and consequently do not belong to the solar system. It seems therefore probable that at all events a certain proportion of the meteoric dust is derived from sources outside the solar system. The Earth and planets, as they are carried along with the Sun in his motion through space, would thus receive a larger proportion of meteoric matter on their northern than on their southern hemispheres, and I would suggest, as a theory worthy of consideration, that this may account for the preponderating mass of the continents in the northern hemisphere of the Earth ...
Gaseous matter is probably continually being added to the atmosphere. ... The total amount of the atmosphere must either be increasing or decreasing. Such an increase or decrease would in time serve to account for great changes of temperature at the Earth’s surface. If we suppose the Earth to pass through a region of space where there are comparatively few meteors, the height of the atmosphere would in the course of time be greatly decreased, and we should have a temperature at the sea level corresponding to the present temperature of our mountain-tops. In the language of geologists, a glacial epoch would be the result. If, on the other hand, the Earth passed through a region of space rich in meteors, containing occluded carbonic acid gas, the atmosphere would increase in depth, and a period like the carboniferous period might be the result, in which a semi-tropical vegetation might again flourish on the coast of Greenland.
It was doubted by scientists whether the fact of our earth passing through a region of space in which there are more or less of meteoric masses has any bearing upon the height of our atmosphere being increased or decreased, or even upon the state of weather. But we think we could easily prove it; and since they accept the fact that the relative distribution and proportion of land and water on our globe may be due to the great accumulation upon it of meteoric dust; snow – especially in our northern regions – being full of meteoric iron and magnetic particles; and deposits of the latter being found even at the bottom of seas and oceans, I wonder how Science has not hitherto understood that every atmospheric change and disturbance was due to the combined magnetism of the two great masses between which our atmosphere is compressed! I call this meteoric dust a ‘mass’ for it is really one. High above our earth’s surface the air is impregnated and space filled with magnetic, or meteoric dust, which does not even belong to our solar system. Science having luckily discovered, that, as our earth with all the other planets is carried along through space, it receives a greater proportion of that dust matter on its northern than on its southern hemisphere, knows that to this are due the preponderating number of the continents in the former hemisphere, and the greater abundance of snow and moisture. Millions of such meteors and even of the finest particles reach us yearly and daily and all our temple knives are made of this ‘heavenly’ iron, which reaches us without having undergone any change – the magnetism of the earth keeping them in cohesion. Gaseous matter is continually added to our atmosphere from the never ceasing fall of meteoric strongly magnetic matter, and yet it seems with them still an open question whether magnetic conditions have anything to do with the precipitation of rain or not! ...
I was under the impression that science was aware that the glacial periods as well as those periods when temperature is ‘like that of the carboniferous age’ – are due to the decrease and increase or rather to the expansion of our atmosphere, which expansion is itself due to the same meteoric presence?
KH also writes: ‘It is now several years that I had an opportunity of reading the deductions of science upon this subject; therefore, unless I go to the trouble of catching up what I may have remained ignorant of, I do not know the latest conclusions of Science.’
It is not very likely that KH would have found a copy of Phipson’s book or Ranyard’s article in the libraries of the Buddhist monasteries in Tibet and India where he often stayed.* We know from the Mahatma Letters that he sometimes researched subjects clairvoyantly,1 and he could have used a technique employed by H.P. Blavatsky when writing her two major works: she was able to summon up before her inner eye, sometimes with the masters’ assistance, the astral counterparts of published writings on a particular topic.2 KH mentions his ‘bad habit’ of never forgetting what he has seen or read, and says ‘I have a habit of often quoting, minus quotation marks – from the maze of what I get in the countless folios of our Akasic libraries, so to say – with eyes shut’; he says that Blavatsky once called him a ‘brain pirate’ because of this.3 The way in which Ranyard’s phrases and ideas are woven into KH’s letter would be consistent with KH having written from memory.
KH mentions the possible link between the amount of dust accreted by the earth and the varying height of the atmosphere, but does not specify the mechanisms involved. He also mentions that gaseous matter is constantly being added to the atmosphere (through the vaporization of meteoric dust) – and this is the mechanism Ranyard invokes to explain the suggested link
It is interesting to note that the discovery that dust particles recovered from the seafloor during the expedition of the HMS Challenger from 1872 to 1876 were extraterrestrial in origin was the first recognition that, in addition to being bombarded with meteorite-sized objects, the earth also accumulates substantial amounts of submillimetre-sized particles (micrometeorites).
KH’s statements quoted above suggest that when he speaks of meteoric dust he means exactly that: meteoric dust. Some theosophical writers, however, have taken the view that KH was not really referring to dust at all. Charles Ryan suggested that KH’s references to ‘meteoric dust’ and a ‘meteoric continent’ around the earth might be ‘clumsy and unsatisfactory terms’ that he was forced to resort to for want of any better western terms.
Since KH spoke of the meteoric continent’s role in generating the earth’s heat, Ryan believed KH was really referring to unexpectedly ‘hot’ atmospheric layers, including what is now called the ionosphere. Ryan, Henry Edge, and Alan Stover drew attention to scientific discoveries, from the late 1920s onwards, of heated layers in the atmosphere at various altitudes, e.g. a warm zone of ozone with a temperature of 90°C at an altitude of 65 to 80 km, and temperatures of over 1000°C above 80 km.*5 G. de Purucker was more cautious, saying that there was only a limited correspondence between such findings and theosophical teachings on the meteoric veil.
*A high temperature need not imply intense, sensible heat. Temperature is a measure of the average speed (or kinetic energy) of atoms and molecules; the faster they move, the higher the temperature. The quantity of heat depends not just on the speed of atoms and molecules but also on their concentration in a given volume of space.7 Although particles etc. in the upper atmosphere are very energetic, they are relatively few and widely separated – so it is far from ‘hot’ up there!
Blair Moffett suggested a very different interpretation of KH’s remarks:
Making allowance for the lack of suitable technical language in the 1880s to describe such phenomena, the words of K.H. strongly suggest the Van Allen radiation belts. Or, more accurately, the cause of those belts: enormous relatively permanent strata of magnetized meteoric matter or dust that function as traps for radiation from the sun and outer space.
The earth has two radiation belts (the inner belt was discovered by Van Allen in 1958). These doughnut-shaped zones are centred on the equator and are occupied by appreciable numbers of energetic protons and electrons trapped in the earth’s magnetic field high above the sensible atmosphere; they screen out high-energy particles continuously bombarding our planet. The inner belt extends from 650 to 6300 km above the terrestrial surface and the outer belt from about 10,000 to 65,000 km.
The above quotation from Moffett is somewhat contradictory. The first sentence implies that KH spoke of ‘meteoric dust’ for want of a better term, whereas the second sentence takes his references to ‘meteoric dust’ at face value and suggests that this dust may actually help to form the radiation belts. To equate the ‘meteoric continent’ with the Van Allen belts seems unwarranted, but could meteoric dust play a role in their formation? The inner belt is believed to be produced by cosmic-ray ions from outer space colliding with atoms of the atmosphere, and the outer belt is thought to be produced by the solar wind (the stream of charged particles emitted by the sun) colliding with and being trapped by the earth’s magnetosphere.9 The official view is that, far from helping to form the radiation belts, meteoric dust tends to reduce them as the dust particles absorb the radiation belt particles.
Terms like ‘ions’ (in the sense of dissociated atoms), ‘plasma’ (in the sense of an ionized gas), ‘cosmic rays’, and ‘solar wind’ did not exist in the 1880s, and the expression ‘magnetic matter’ may refer to such phenomena, as well as to more ethereal states of matter.11 But ‘meteoric dust’ is a very specific term, and KH’s remarks on the subject, as well as later comments by De Purucker, generally seem to be meant quite literally, and should therefore be compared with current knowledge about dust concentrations within and beyond the earth’s atmosphere. Referring to the term ‘meteoric continent’, De Purucker points out that ‘continent’ is being used in its original Latin sense of ‘to contain’ or ‘to enclose’ – the earth being enclosed within a shell of meteoric dust. He also says that ‘meteoric continent’ can refer to astral matter as well as physical matter; the astral earth provides a matrix, as it were, for the physical earth and its operations.
There is some ambiguity in theosophical writings as to where exactly the meteoric veil lies. It is sometimes said to exist above the earth’s atmosphere, which is ‘compressed’ between the ‘continent’ of meteoric matter and the body of the earth. But KH also says that ‘High above our earth’s surface the air is impregnated and space filled with magnetic, or meteoric, dust’. This suggests that the meteoric veil refers to dust concentrations both within the atmosphere and above it. But even this is ambiguous as the earth’s atmosphere gradually thins with height, and has no well-defined upper boundary.
In the latter half of the 19th century, the atmosphere was thought to extend to a height of about 70 km before its properties become significantly affected by the extreme rarefaction of the air. However, several scientists argued that there must be some kind of atmosphere – possibly even an envelope of electricity – extending to an even greater altitude, estimated at 320 or even 800 km.
The lowest, thinnest, and densest atmospheric layer is the troposphere, whose upper boundary (the tropopause) ranges in height from 18 km in the tropics to 6 km in the polar regions. Most meteorological phenomena occur in the troposphere, which accounts for about 80% of the atmospheric mass. The lower 50 km of the atmosphere, comprising the troposphere and stratosphere, contains over 99% of the atmospheric mass. The outermost layer of the atmosphere, known as the exosphere, extends over a thousand kilometres above the earth, before fading into the interplanetary medium.
As explained in section 4, the earth’s gravitational attraction and its motion through space result in a constant influx of meteoroids* of different sizes. The zone between about 110 and 80 km altitude is known as the meteor region, as the air becomes sufficiently dense to cause high-velocity meteors to burn up, leaving fiery trails in the night sky. Many meteoric dust particles also melt and evaporate in this zone. The densest belt of cosmic dust occurs at an altitude of about 85 km, near the top of the mesosphere.
*Meteoroids are any small solid objects moving in interplanetary space, generally smaller than an asteroid and larger than a molecule. They are known as meteors when passing through the atmosphere and as meteorites if they reach the earth’s surface intact.
3. Atmosphere and heat
The atmosphere consists of 78% nitrogen, 21% oxygen, and small amounts of argon, water vapour, carbon dioxide, ozone, and other gases. Water vapour is believed to play a major role in regulating air temperature because it absorbs solar energy and thermal radiation from the planet’s surface. The troposphere contains 99% of the water vapour in the atmosphere; the water vapour content decreases rapidly with altitude, resulting in an average vertical temperature decrease of 6°C per km. The stratosphere contains little water vapour but about 90% of the ozone in the atmosphere; the ozone layer is located at altitude of 20-30 km. Ozone absorbs solar ultraviolet radiation, thereby heating the stratosphere. In the mesosphere gases are thin and concentrations of ozone and water vapour are negligible, with the result that the temperature drops to -120°C at the mesopause. In the thermosphere the gases are even thinner, but the temperature rises to about 2000°C at the top of the layer, 700 km above earth’s surface, due to the absorption of intense solar radiation by the limited amount of remaining molecular oxygen.
KH says that the heat the earth receives by radiation from the sun is at most one third of the amount it receives directly from the mass of meteoric dust above its surface. He also states: ‘The absorption of Solar Forces by the earth is tremendous; yet it is, or may be demonstrated that the latter receives hardly 25 per cent. of the chemical power of its rays, for these are despoiled of 75 per cent. during their vertical passage through the atmosphere at the moment they reach the outer boundary of “the aerial ocean.” And even those rays lose about 20 per cent. in illuminating and caloric power – we are told by science.
According to modern science, 50% of the solar radiation reaching earth passes through the atmosphere to the planet’s surface: the atmosphere transmits 33% of incoming radiation, and an additional 17% reaches the surface as scattered energy. However, solar radiation accounts for only one third of the energy reaching the surface; sky radiation accounts for two thirds. Of the energy received by the atmosphere, 77% comes from earth, and only 13% from direct absorption of solar radiation. However, the sole ultimate energy source driving the atmosphere is believed to be the sun.
Conventional science’s understanding of the sun and of the earth’s atmosphere and energy balance is bound to be defective given that it takes no account of the subtler, ethereal grades of matter-energy that form the substratum of the physical world. Alternative approaches are being developed by a number of independent ‘ether scientists’. For instance, Paulo and Alexandra Correa – building on the pioneering experimental and theoretical work of Nicola Tesla, Wilhelm Reich, and Harold Aspden – have reached a number of conclusions diametrically opposed to those of orthodox science.
According to textbook science, the sun emits electromagnetic radiation (including ultraviolet, visible, and infrared radiation), which travels through the vacuum of space as transverse waves at the speed of light, and this radiation is then partially filtered and transformed when it enters the earth’s atmosphere. The Correas, on the other hand, argue that the sun mainly emits aether* radiation, which travels through space as longitudinal waves, not limited by the speed of light, and that on entering the earth’s atmosphere aether energy interacts with physical matter to produce electromagnetic radiation (photons).5 They also demonstrate that official chemistry fails to explain the basic atmospheric cycle of oxygen, ozone, and water, and show how the creation of electrons and photons from aether energy can resolve the problem – a process accompanied by the release of heat.
*Several ether scientists prefer the spelling ‘aether’, to distinguish this subtler energy-substance from the volatile liquid known as ‘ether’. In theosophy, ‘aether’ is often reserved for grades of nonphysical matter higher than the etheric grades directly involved in the manifestation of physical matter and forces.
Mainstream science is unable to explain what light (electromagnetic radiation) really is. It tries to conceal its ignorance behind the profound-sounding term ‘wave-particle duality’. All this means is that light sometimes displays properties expected of particles (photons), and sometimes properties expected of waves. Since mainstream science has abolished the ether there is actually nothing for the waves to wave in, but that does not seem to worry orthodox scientists.
Referring to the conflict between the corpuscular (particle) and undulatory (wave) theories of light in her own day, Blavatsky stated that occult science did not reject the undulatory theory but that it required ‘completion and rearrangement’. She stressed that light was associated with ethereal matter, quoted approvingly from scientists who contended that the sun emitted ethereal energy, and mentioned the role of the earth’s atmosphere in the transformation of incoming solar energies. G. de Purucker says that solar radiation interacts with the meteoric veil encircling earth to produce electromagnetic currents in the atmosphere, which play back and forth between earth and sky (especially the meteoric veil). Solar rays and electricity themselves are neither hot nor cold, but arouse vibratory activity in whatever they touch or pass through, which we may sense as light or heat.
Modern science recognizes that electromagnetic interchanges take place between earth and various constituents of the atmosphere. Atmospheric matter reradiates the energy it receives from solar radiation; cloud bases and atmospheric gases (such as carbon dioxide), for example, radiate infrared (heat) radiation. The earth’s land and ocean surfaces reradiate infrared energy to the atmosphere, where most of it is absorbed by water vapour and carbon dioxide and reradiated to earth.
Regarding Ranyard’s argument that if the earth passed through a region of space rich in meteors containing ‘carbonic acid gas’ (i.e. carbon dioxide), the atmosphere would increase in depth, producing global warming, astronomer Bill Napier comments: ‘the carbon dioxide budget of the Earth’s surface is so enormous that that contained in meteoroidal material is unlikely to be relevant: even in cometary material it’s at the few percent level’. Moreover, because gases are compressible, adding gas to the atmosphere will not necessarily increase its volume. For the height of the atmosphere to change significantly, a substantial change in its composition or temperature is required.*9 Since nitrogen and oxygen together make up 99% of the atmospheric mass, the influx of meteoric dust is unlikely to bring about major changes in atmospheric composition.
*The height of the atmosphere is of the order h = RT/µg where R is the gas constant, T is temperature (in kelvins), µ is molecular weight, and g is the earth’s surface gravity. In cgs units, with R = 8.3 x 107, g = 10ł, T = 300, and µ = 30, we get a characteristic height of about 8 km, which agrees well with the depth of the troposphere. Since R and g are fixed, changes in h must come through changes in T or µ.
Dust can however have a major impact on global temperature , which would cause the lower atmosphere to expand or contract slightly. Even today the tropopause height varies with latitude, season, and weather; it is higher at the equator than at the poles, and higher in summer than in winter. In addition, since 1980 the tropopause has risen about 20 metres, and this has been attributed to the expansion of the troposphere due to the buildup of greenhouse gases (global warming), and the contraction of the stratosphere due to ozone depletion.
4. Scientific findings
On the morning of 14 December 1807, a huge fireball flashed across the southwestern Connecticut sky and rocks were reported falling to earth. Two Yale professors went to investigate and finally concluded that the rocks were of extraterrestrial origin – i.e. meteorites. When President Thomas Jefferson, who was also a scientist, heard their report, he allegedly said, ‘Gentlemen, I would rather believe that two Yankee professors would lie than believe that stones fall from heaven.’ Science has come a long way since then!
The inner solar system is enveloped by a tenuous cloud of dust known as the zodiacal cloud. It comprises dust bands associated with asteroid families, dust trails associated with short-period comets, and a ring of asteroidal dust locked in resonance with the earth’s orbit.2 Most interplanetary dust particles are thought to be derived from asteroid collisions and cometary activity, but the relative contribution made by these two sources is a matter of controversy. Other dust sources include interstellar dust grains, ejecta from impacts on the moon and Mars, and collisions in the inner solar system and the Kuiper Belt beyond Pluto. Most dust particles in the inner solar system move in prograde (counterclockwise) orbits (as do the planets), and gradually spiral in towards the sun.
The reflection of sunlight from the zodiacal cloud is believed to give rise to the zodiacal light – a very faint cone of light in the sky, visible in the east just before sunrise and in the west just after sunset; on very clear nights the glow extends along the ecliptic (the plane of the earth’s orbit around the sun). Reflected sunlight also produces the gegenschein (’counter glow’), a bright, diffuse patch in the night sky directly opposite the sun.
The motion of the sun and planets through the interstellar medium results in a stream of interstellar gas and dust grains moving through the solar system in the opposite direction to the sun’s motion. Interstellar dust is also entering the solar system from several other directions. In 1992/93, the Ulysses spacecraft detected a stream of very small interstellar grains near Jupiter coming from the approximate direction of the galactic centre (where star densities are largest), and at certain times in the solar cycle these particles are expected to reach earth. By contrast, radiation pressure and interaction of charged dust grains with the interplanetary magnetic field prevent even smaller interstellar grains from penetrating far into the solar system. Ion trails of larger dust particles have been detected entering the earth’s atmosphere at velocities that significantly exceed the solar system escape velocity, identifying these particles as interstellar.
The earth itself is surrounded by a substantial cloud of interplanetary and interstellar dust, stretching, in decreasing density, for 150,000 km or so before fading out to the usual density of the interplanetary medium. An estimated 40,000 tonnes of cosmic dust currently rains down on earth every year.5 Dust particles are continuously entering the atmosphere, and then take up to several years to reach the earth’s surface. They span a range of sizes from submicron* to millimetres in diameter, and a range of velocities from 11.1 km/s (earth escape velocity) to 72 km/s (solar system escape velocity). Submillimetre cosmic dust accounts for most of the extraterrestrial matter being accreted by the earth. The most spectacular manifestations of dust influx to the earth are meteor showers and the far rarer and more intense meteor storms, caused by the earth’s passage through narrow streams of debris (meteor streams) left in the wake of short-period comets or earth-crossing asteroids.
All extraterrestrial material that impacts the earth’s atmosphere is accreted, but only a fraction survives as solid matter. Most of the extraterrestrial particles impacting the top of the atmosphere are around 200 µm in diameter. Many of the particles this size and larger undergo extensive melting and vaporization, and ablate at altitudes of between about 75 and 110 km. Meteor vapour is believed to recondense to form submicron particles that eventually attach to larger atmospheric particles before reaching the earth’s surface. While larger and faster particles generally melt or partly vaporize, smaller and slower particles tend to survive atmospheric entry. Objects in the centimetre to metre range are slowed by atmospheric friction and survive impact, yielding the meteorites that have been collected at the earth’s surface. Objects larger than a few tens of metres hit the earth’s surface at high velocities and are largely melted or vaporized, leaving impact craters. Meteoroids are composed mainly of iron, magnesium and silicon oxides, with carbon occasionally present in substantial amounts.
One of the factors affecting how much interplanetary material the earth sweeps up is the inclination of the earth’s orbit to what is known as the invariable plane of the solar system (defined as: the plane through the centre of mass of the solar system perpendicular to the angular momentum vector of the solar system). This is the plane in which most interplanetary dust tends to concentrate, and it approximately coincides with the orbital plane of Jupiter.
The current location of the celestial north pole, ecliptic north pole, and invariable-plane north pole. It is theorized that planetary gravitational influences cause the ecliptic poles (the two points in space perpendicular to the plane of the earth’s orbit) to circle the poles of the invariable plane with a period of 70,000 years, while the inclination of the ecliptic in relation to the invariable plane oscillates between 0.8° and 2.6° over a period of about 100,000 years. Its current inclination is 1.58°; its last maximum was about 30,000 years ago, and it is expected to decrease to a minimum in about 20,000 years.
If the dust in the zodiacal ring is confined to the invariable plane, and the earth’s inclination to it is high, the earth passes through the dust band only twice per year. But when the inclination is low, the earth stays in the dust band for the entire orbit and much more dust is accreted. Data on meteoric showers indicate that the maximum total meteoric influx to earth occurs on dates coincident with earth’s passage through the invariable plane (early July and early January). In reality, the situation is more complicated than this: there are several dust bands, and their midplanes are warped, with the degree of warping depending on the size of the particles concerned. Earth’s current orbital inclination with respect to the earth-crossing portion of dust bands composed of 4-24 µm particles ranges from just under 2° to 5°.
Dust is a major factor influencing the earth’s climate, as it affects the atmosphere’s transparency to incoming solar radiation and outgoing heat. Clouds are the most important element in reflecting solar radiation back into space, and clouds and precipitation depend on the amount of aerosols (small particles) in the atmosphere, including dust thrown up by volcanic eruptions and meteoric dust from space. Some dust particles reduce insolation by direct scattering of sunlight, but cometary particles could cause warming by injecting water into the atmosphere. Volcanic eruptions producing a large amount of aerosols over much of the earth, such as Tambora (1815), Krakatoa (1883), and Agung (1963) have caused global cooling of up to a degree for a year or two after the eruption.
Meteoric dust therefore plays a crucial role in the atmosphere by acting as nucleation sites for cloud growth, especially in the stratosphere and mesosphere where terrestrial dust has trouble reaching, except in the event of major volcanic eruptions. Meteoric dust particles provide condensation nuclei for noctilucent clouds, which form in summer time in the upper mesosphere above the polar regions (80-100 km altitude). Meteoric dust is responsible for the formation of metal atom and ion layers in the ionosphere and mesosphere, and affects the properties of the lower (D and E) regions of the ionosphere (60-150 km altitude). In the stratosphere, meteoric dust serves as condensation nuclei for sulphuric acid and water droplets, and for polar stratospheric clouds that play a critical role in the destruction of the ozone layer. Accreted dust may also affect cloud cover by modulating stratospheric electric currents.
There is evidence that the solar system is surrounded by a cloud of dust and cometary debris, probably of interstellar origin. This dust may enter the solar system under certain conditions, despite the expelling action of the solar wind. Paul LaViolette argues that volleys of cosmic rays emitted by periodic galactic core explosions could push large amounts of cosmic dust into the solar system, bringing about global warming or cooling on earth, depending on the prevailing conditions.12 The influx of interstellar dust will also increase when the solar system periodically passes through denser regions of the interstellar medium. Some ice core studies suggest that at certain times during the last ice age cosmic dust was accumulating on the earth’s surface hundreds of times faster than it does today, though this claim has been disputed.
The general belief is that over an extended timescale the accretion rate of asteroidal interplanetary dust particles (IDPs) should vary by a factor of only two or three. However, rare giant comets are the most massive bodies entering the inner solar system and are major contributors to the zodiacal cloud, generating large surges of cometary dust onto earth. Bill Napier argues that the cometary dust influx can occasionally approach a million tons per year for periods of several millennia. Moreover, since submicron particles are efficient scatterers of optical light, if earth were to pass through the coma or tail of a very large comet, enough dust might enter the upper atmosphere to darken the sun, with a catastrophic effect on photosynthesis and the food chain.
Napier speculates that the 100,000-year cycle seen in climatic records may be caused by the orbital precessions of Jupiter and Saturn, as these planets largely control the entry of short-period comets into the inner solar system. This climatic cycle, which has been dominant for the past million years, is usually attributed to variations in the eccentricity of the earth’s orbit, but this explanation faces many problems. Another alternative explanation, proposed by Muller and MacDonald, is that this cycle is due to the periodic alteration in the angle between the ecliptic and the invariable plane of the solar system.However, this explanation too has attracted criticism; for instance, earth’s orbital inclination with respect to the earth-crossing dust bands does not vary in a smooth periodic fashion.
It is thus well established that the influx of meteoric dust is a significant factor influencing the atmosphere and global climate, though major disagreements about the climate system remain.