Ferromagnetic crystals (magnetite?) in human tissue

In recent years, a variety of animals have been found which are able to synthesize the ferromagnetic mineral magnetite (Fe3O4). Lowenstam (1962) originally recognized biogenic magnetite in the radular teeth of a primitive marine mollusc, the chiton (Polyplacophora), and since then it has been identified as a precipitate in several magnetically sensitive organisms, including honey bees (Gould, Kirschvink & Deffeyes, 1978), homing pigeons (Walcott, Gould & Kirschvink, 1979) and in magnetotactic bacteria (Frankel, Blakemore & Wolfe, 1979). Zoeger, Dunn & Fuller (1980) also report a localized concentration of magnetite in dolphin heads, although magnetosensory behavioural experiments have not as yet been done on them. Magnetite is biologically unique because it is both ferromagnetic and conducts electricity like a metal; consequently it interacts strongly with magnetic and electric fields. Due to the numerous industrial and research environments which expose people to artificially intense electromagnetic conditions, it is of importance to know whether or not this material might exist in human tissue. Kirschvink & Gould (1980) have argued that there are probably one or more non-sensory metabolic functions for magnetite from which specialized magnetoreceptors could have evolved; consequently one might expect to find small amounts of magnetite in all animals, including humans. In an attempt to partially answer this question, I searched for magnetic remanence in four intact human adrenal glands which had been removed during autopsy and were frozen quickly in non-magnetic containers. Results of this analysis are shown on Fig. 1. Indeed, there is a measurable amount of high-coercivity ferromagnetic material present which appears to be finely disseminated throughout the tissue. Between 1 and 10 million single-domain magnetite crystals per gram would be necessary to account for the observed magnetic remanence. Although these measurements do not uniquely identify the crystal phase as magnetite, no other ferromagnetic minerals have ever been observed as biologic precipitates. Positive identification, of course, awaits the development of magnetic separation techniques capable of isolating and purifying these submicroscopic crystals. Barnothy & Sümegi (1969) have shown that mouse adrenals are particularly prone to degeneration in moderately strong magnetic fields; this effect might be due to the presence of magnetite

The Earth's Worst Climate Disaster

Scientists, environmentalists, and the wiser members of the political class worry today about global climate change. Will rising tides plunge Tokyo, London, and New York beneath the ocean’s waves? Will meltwater pouring off of North America shift the circulation of the North Atlantic Ocean and plunge Europe into an Ice Age? Yet, as worrisome as these prospects are, the Earth has faced far greater climatic catastrophes in the past. The greatest among these was the Paleoproterozoic Snowball Earth event, which 2.3 billion years ago smothered the planet with a blanket of ice for tens of millions of years

The identification and biogeochemical interpretation of fossil magnetotactic bacteria

Magnetotactic bacteria, which most commonly live within the oxic-anoxic transition zone (OATZ) of aquatic environments, produce intracellular crystals of magnetic minerals, specifically magnetite or greigite. The crystals cause the bacteria to orient themselves passively with respect to the geomagnetic field and thereby facilitate the bacteria’s search for optimal conditions within the sharp chemical gradients of the OATZ. The bacteria may also gain energy from the redox cycling of their crystals. Because magnetotactic bacteria benefit from their magnetic moments, natural selection has promoted the development of traits that increase the efficiency with which the intracellular crystals impart magnetic moments to cells. These traits also allow crystals produced by magnetotactic bacteria (called magnetofossils when preserved in sediments) to be distinguished from abiogenic particles and particles produced as extracellular byproducts of bacterial metabolism. Magnetofossils are recognizable based on their narrow size and shape distributions, distinctive morphologies with blunt crystal edges, chain arrangement, chemical purity, and crystallographic perfection. This article presents a scheme for rating magnetofossil robustness based on these traits. The magnetofossil record extends robustly to the Cretaceous and with lesser certainty to the late Archean. Because magnetotactic bacteria predominantly live in the OATZ, the abundance and character of their fossils can reflect environmental changes that alter the chemical stratification of sediments and the water column. The magnetofossil record therefore provides an underutilized archive of paleoenvironmental information. Several studies have demonstrated a relationship between magnetofossil abundance and glacial/interglacial cycles, likely mediated by changes in pore water oxygen levels. More speculatively, a better-developed magnetofossil record might provide constraints on the long-term evolution of marine redox stratification. More work in modern and ancient settings is necessary to explicate the mechanisms linking the abundance and character of magnetofossils to ancient biogeochemistry

Paleoproterozic Icehouses and the Evolution of Oxygen Mediating Enzymes: The Case for a Late Origin of Photosystem -- II

Two major geological problems regarding the origin of oxygenic photosynthesis are: (1) identifying a source of oxygen predating biological oxygen production and capable of driving the evolution of oxygen tolerance, and (2) determining when oxygenic photosynthesis evolved. One solution to the first problem is the accumulation of photochemically-produced H2O2 at the surface of glaciers and its subsequent incorporation into ice. Melting at the glacier base would release H2O2, which interacts with seawater to produce O2 in an environment shielded from the lethal levels of ultraviolet radiation needed to produce H2O2. Answers to the second problem are controversial and range from 3.8 to 2.2 Ga. A skeptical view, based on metals that have redox potentials close to oxygen, argues for the late end of the range. The preponderance of geological evidence suggests little or no oxygen in the late Archaean atmosphere (< 1 ppm). The main piece of evidence for an earlier evolution of oxygenic photosynthesis comes from lipid biomarkers. Recent work, however, has shown that 2-methylhopanes, once thought to be unique biomarkers for cyanobacteria, are also produced anaerobically in significant quantities by at least two strains of anoxygenic phototrophs. Sterane biomarkers provide the strongest evidence for a date ≥2.7 Ga but could also be explained by the common evolutionary pattern of replacing anaerobic enzymes with oxygen-dependent ones. Although no anaerobic sterol synthesis pathway has been identified in the modern biosphere, enzymes that perform the necessary chemistry do exist. This analysis suggests that oxygenic photosynthesis could have evolved close in geological time to the Makganyene Snowball Earth Event and argues for a causal link between the two

Rock magnetism linked to human brain magnetite

Magnetite has a long and distinguished career as one of the most important minerals in geophysics, as it is responsible for most of the remanent magnetization in marine sediments and the oceanic crust. It may come as a surprise to discover that it also ranks as the third or fourth most diverse mineral product formed biochemically by living organisms, and forms naturally in a variety of human tissues [Kirschvink et al., 1992]. Magnetite was discovered in teeth of the Polyplacophora mollusks over 30 years ago, in magnetotactic bacteria nearly 20 years ago, in honey bees and homing pigeons nearly 15 years ago, but only recently in human tissue

Late Proterozoic Low-Latitude Global Glaciation: the Snowball Earth

A fundamental question of earth history concerns the nature of the Late Proterozoic glaciogenic sequences that are known from almost all of the major cratonic areas, including North America, the Gondwana continents, and the Baltic Platform. A major controversy involves the probable latitude of formation for these deposits- were they formed at relatively high latitudes, as were those of the Permian and our modern glacial deposits, or were many of them formed much closer to the equator? Arguments supporting a low depositional latitude for many of these units have been discussed extensively for the past 30 years (e.g., Harland 1964), beginning with the field observations that some of the diamictites had a peculiar abundance of carbonate fragments, as if the ice had moved over carbonate platforms. Indeed, many of these units, such as the Rapitan Group of the Canadian Cordillera, are bounded above and below by thick carbonate sequences which, at least for the past 100 Ma, are only known to have been formed in the tropical belt within about 33° of the equator (Ziegler et al. 1984). Other anomalies include dropstones and varves in the carbonates, as well as evaporites (for a complete review, see Williams 1975). Either the earth was radically different during the late Precambrian glacial episode(s), or the major continental land masses spent an extraordinary amount of time traversing back and forth between the tropics and the poles

Red Earth, White Earth, Green Earth, Black Earth

Oxygen drives the biosphere—we can’t live without it. But most scientists now agree that there was no free oxygen in the air during the earliest portion of Earth’s history. The first oxygen came from a group of bacteria—the cyanobacteria—that had developed a new method of photosynthesis. Their method was so efficient that they spread rapidly throughout the oceans of the world and overtook their less-efficient predecessors. But their success may have created a catastrophic climate disaster that plunged Earth into a global deep freeze for tens of millions of years and almost wiped out life on the planet forever. That, at least, is a scenario I have developed in collaboration with geobiology grad student Bob Kopp

Ferromagnetism in two mouse tumours

A variety of living organisms has been found recently that are biochemically able to precipitate the ferromagnetic mineral magnetite (Fe3O4). Originally discovered in the radular teeth of a primitive marine mollusc (Lowenstam, 1962), magnetite has since been reported in bacteria (Frankel, Blakemore & Wolfe, 1979), arthropods (Gould, Kirschvink & Deffeyes, 1978), and vertebrates (Walcott, Gould & Kirschvink, 1979; Zoeger, Dunn & Fuller, 1981; Walker & Dizon, 1981). Although the presence and biological origin of this material are clear, very little is yet known about the distribution or metabolic function of ferromagnetic minerals in vertebrate tissue. Magnetic remanence, which uniquely indicates the presence of ferromagnetic particles, has been previously detected in localized areas associated with the dura membranes of homing pigeons (Walcott et al. 1979) and dolphins (Zoeger et al. 1981), in pigeon neck muscles (Presti & Pettigrew, 1980), in the mid-brain of monkeys, and in human adrenal glands (Kirschvink, 1981). We report here the first discovery of anomalously high concentrations of ferromagnetic material in two strains of neoplasms, YC-8 lymphoma and Lewis lung tumour, as well as the apparent absence of such material in three human carcinomas (gastric, colon and renal)

Comment on "Constraints on biological effects of weak extremely-low-frequency electromagnetic fields"

In a recent paper, Adair [Phys. Rev. A 43, 1039 (1991)] concludes that weak extremely-low-frequency (ELF) electromagnetic fields cannot affect biology on the cell level. However, Adair’s assertion that few cells of higher organisms contain magnetite (Fe_(3)O_4) and his blanket denial of reproducible ELF effects on animals are both wrong. Large numbers of single-domain magnetite particles are present in a variety of animal tissues, including up to a hundred million per gram in human brain tissues, organized in clusters of tens to hundreds of thousand per gram. This is far more than a "few cells." Similarly, a series of reproducible behavioral experiments on honeybees, Apis mellifera, have shown that they are capable of responding to weak ELF magnetic fields that are well within the bounds of Adair’s criteria. A biologically plausible model of the interaction of single-domain magnetosomes with a mechanically activated transmembrane ion channel shows that ELF fields on the order of 0.1 to 1 mT are capable of perturbing the open-closed state by an energy of kT. As up to several hundred thousand such structures could fit within a eukaryotic cell, and the noise should go as the square root of the number of independent channels, much smaller ELF sensitivities at the cellular level are possible. Hence, the credibility of weak ELF magnetic effects on living systems must stand or fall mainly on the merits and reproducibility of the biological or epidemiological experiments that suggest them, rather than on dogma about physical implausibility