Paleolightning
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Paleolightning refers to the remnants of ancient lightning activity studied in fields such as
historical geology Historical geology or palaeogeology is a discipline that uses the principles and methods of geology to reconstruct the geological history of Earth. Historical geology examines the vastness of geologic time, measured in billions of years, and inve ...
, geoarchaeology, and fulminology. Paleolightning provides tangible evidence for the study lightning activity in Earth's past and the roles lightning may have played in Earth's history. Some studies have speculated that lightning activity played a crucial role in the development of not only Earth's early atmosphere but also early life. Lightning, a non-biological process, has been found to produce biologically useful material through the
oxidation and reduction Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
of inorganic matter. Research on the impact of lightning on Earth's atmosphere continues today, especially with regard to feedback mechanisms of lightning-produced nitrate compounds on atmospheric composition and global average temperatures. Detecting lightning activity in the geologic record can be difficult, given the instantaneous nature of lightning strikes in general. However,
fulgurite Fulgurites (), commonly known as "fossilized lightning", are natural tubes, clumps, or masses of sintered, vitrified, and/or fused soil, sand, rock, organic debris and other sediments that sometimes form when lightning discharges into ground. ...
, a glassy tube-like, crust-like, or irregular mineraloid that forms when lightning fuses
soil Soil, also commonly referred to as earth or dirt Dirt is an unclean matter, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty. Common types of dirt include: * Debri ...
, quartz sands,
clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...
, rock, biomass, or
caliche Caliche () is a sedimentary rock, a hardened natural cement of calcium carbonate that binds other materials—such as gravel, sand, clay, and silt. It occurs worldwide, in aridisol and mollisol soil orders—generally in arid or semiarid regions ...
is prevalent in electrically active regions around the globe and provides evidence of not only past lightning activity, but also patterns of
convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the conve ...
. Since lightning channels carry an electric current to the ground, lightning can produce
magnetic fields A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
as well. While lightning-magnetic anomalies can provide evidence of lightning activity in a region, these anomalies are often problematic for those examining the magnetic record of rock types because they disguise the natural magnetic fields present.


Lightning and early Earth

The atmospheric composition of early Earth (the first billion years) was drastically different from its current state. Initially,
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
and
helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
compounds dominated the atmosphere. However, given the relatively small size of these elements and the warmer temperature of Earth compared to other planets at the time, most of these lighter compounds escaped, leaving behind an atmosphere composed mainly of
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
,
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
,
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
and
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
with small concentrations of hydrogen compounds and other gases. The atmosphere was transitioning from a reduction atmosphere (an atmosphere that inhibits oxidation) to one of
oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
, similar to our current atmosphere. The origin of life on Earth has been a matter of speculation for quite some time. Living things did not spontaneously appear, so some sort of biological or even non-biological process must have been responsible for the generation of life. Lightning is a non-biological process, and many have speculated that lightning was present on early Earth. One of the most famous studies that investigated lightning on the early Earth was the Miller–Urey experiment.


Miller–Urey experiment

The Miller–Urey experiment sought to recreate the early Earth atmosphere within a laboratory setting to determine the chemical processes that ultimately led to life on Earth. The basis of this experiment was leveraged on Oparin's hypothesis, which assumed that some organic matter could be created from inorganic material given a reduction atmosphere. Using a mixture of water,
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
,
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
, and
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
in glass tubes, Miller and Urey replicated the effects of lightning on the mixture using
electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials d ...
s. At the conclusion of the experiment, as much as 15 percent of the carbon from the mixture formed organic compounds, while 2 percent of the carbon formed
amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...
s, a necessary element for the building blocks of living organisms.


Volcanic lightning on early Earth

The actual composition of the atmosphere of the early Earth is an area of great debate. Varying amounts of certain gaseous constituents can greatly impact the overall effect of a particular process, which includes non-biological processes such as the buildup of charge in
thunderstorm A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorms are some ...
s. It has been argued that volcano-induced lightning in the early stages of Earth's existence, because the volcanic plume was composed of additional "reducing gases", was more effective at stimulating the
oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
of organic material to accelerate the production of life. In the case of volcanic lightning, the lightning discharge almost exclusively occurs directly within the volcanic plume. Since this process occurs fairly close to ground level, it has been suggested that volcanic lightning contributed to the generation of life to a greater extent than lightning produced within clouds that would lower positive or negative charge from a cloud to the ground. Hill (1992) quantified this enhanced contribution by examining estimated hydrogen cyanide (HCN) concentrations from volcanic lightning and "general lightning". Results showed that HCN concentrations for volcanic lightning were an order of magnitude larger than "general lightning". Hydrogen cyanide is yet another compound that has been linked to the generation of life on Earth. However, given that the intensity and amount of volcanic activity during the early stages of Earth's development is not fully understood, hypotheses regarding past volcanic activity (e.g., Hill, 1992) are usually based on present-day observed volcanic activity.


Nitrogen fixation and lightning

Nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
, the most abundant gas in our atmosphere, is crucial for life and a key component to various biological processes. Biologically usable forms of nitrogen, such as nitrates and
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
, arise via biological and non-biological processes through
nitrogen fixation Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmo ...
. One example of a non-biological process responsible for nitrogen fixation is lightning. Lightning strikes are short-lived, high-intensity electrical discharges that can reach temperatures five times hotter than the surface of the Sun. As a result, as a lightning channel travels through the air,
ionization Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecul ...
occurs, forming nitrogen-oxide (NOx) compounds within the lightning channel. Global production as a result of lightning is around 1–20 Tg N yr−1. Some studies have implied that lightning activity may be the "greatest contributor to the global nitrogen budget", even larger than the burning of fossil fuels. With anywhere between 1500 and 2000
thunderstorms A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorms are somet ...
and millions of lightning strikes occurring daily around the Earth, it is understandable that lightning activity plays a vital role in nitrogen fixation. While nitrogen oxide compounds are produced as a lightning channel travels toward the ground, some of those compounds are transferred to the
geosphere There are several conflicting usages of geosphere, variously defined. It may be taken as the collective name for the lithosphere, the hydrosphere, the cryosphere, and the atmosphere. The different collectives of the geosphere are able to exchange ...
via wet or dry deposition. Variations of nitrogen in terrestrial and oceanic environments impact
primary production In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through ...
and other biological processes. Changes in primary production can impact not only the
carbon cycle The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. Carbon is the main component of biological compounds as well as a major componen ...
, but also the
climate system Earth's climate system is a complex system having five interacting components: the atmosphere (air), the hydrosphere (water), the cryosphere (ice and permafrost), the lithosphere (earth's upper rocky layer) and the biosphere (living things). '' ...
.


The lightning-biota climatic feedback

The lightning-biota climatic feedback (LBF) is a negative feedback response to
global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
on a time scale of hundreds or thousands of years, as a result of increased concentrations of
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
compounds from lightning activity deposited into biological
ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...
s. A zero-dimension Earth conceptual model, which took into account global temperature, soil available nitrogen, terrestrial vegetation, and global atmospheric
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
concentration, was used to determine the response of global average temperatures to increased concentrations from lightning strikes. It was hypothesized that as a result of increasing global average temperatures, lightning production would increase because increased evaporation from oceans would promote enhanced
convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the conve ...
. As a result of more numerous lightning strikes,
nitrogen fixation Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmo ...
would deposit more biologically useful forms of nitrogen into various
ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...
s, encouraging
primary production In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through ...
. Impacts on primary production would affect the
carbon cycle The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. Carbon is the main component of biological compounds as well as a major componen ...
, leading to a reduction in atmospheric carbon dioxide. A reduction in atmospheric carbon dioxide would result in a negative feedback, or cooling, of the
climate system Earth's climate system is a complex system having five interacting components: the atmosphere (air), the hydrosphere (water), the cryosphere (ice and permafrost), the lithosphere (earth's upper rocky layer) and the biosphere (living things). '' ...
. Model results indicated that, for the most part, the lightning-biota climatic feedback retarded positive perturbations in atmospheric carbon dioxide and temperature back to an "equilibrium" state. Impacts of the lightning-biota climatic feedback on curbing anthropogenic influences on atmospheric carbon dioxide concentrations were investigated as well. Using current levels of atmospheric carbon dioxide and rates of increase of atmospheric carbon dioxide on a yearly basis based on the time of the article, the lightning-biota climatic feedback once again showed a cooling effect on global average temperatures, given an initial perturbation. Given the simplified nature of the model, several parameters (
ozone Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...
produced by lightning, etc.) and other feedback mechanisms were neglected, so the significance of the results is still an area of discussion.


Lightning in the geologic record

Indicators of lightning activity in the geologic record are often difficult to decipher. For example,
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
charcoals from the Late
Triassic The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...
could potentially be the result of lightning-induced wildfires. Even though lightning strikes are, for the most part, instantaneous events, evidence of lightning activity can be found in objects called
fulgurite Fulgurites (), commonly known as "fossilized lightning", are natural tubes, clumps, or masses of sintered, vitrified, and/or fused soil, sand, rock, organic debris and other sediments that sometimes form when lightning discharges into ground. ...
s.


Fulgurites

Fulgurites (from the
Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
''fulgur'', meaning "
lightning Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions, both in the atmosphere or with one on the ground, temporarily neutralize themselves, causing the instantaneous release of an avera ...
") are natural tubes, clumps, or masses of sintered, vitrified, and/or fused soil, sand, rock, organic debris and other sediments that sometimes form when lightning discharges into ground. Fulgurites are classified as a variety of the mineraloid
lechatelierite Lechatelierite is silica glass, amorphous SiO2, non-crystalline mineraloid. Structure Lechatelierite is a mineraloid as it does not have a crystal structure. Although not a true mineral, it is often classified in the quartz mineral group. Formati ...
. Fulgurites have no fixed composition because their chemical composition is determined by the physical and chemical properties of material struck by lightning. When lightning strikes a grounding substrate, upwards of 100 million volts (100 MV) are rapidly discharged into the ground. This charge propagates into and rapidly vaporizes and melts
silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...
-rich
quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
ose
sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class o ...
, mixed
soil Soil, also commonly referred to as earth or dirt Dirt is an unclean matter, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty. Common types of dirt include: * Debri ...
,
clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...
, or other sediments. This results in the formation of hollow and/or branching assemblages of glassy,
protocrystalline A protocrystalline phase is a distinct phase occurring during crystal growth which evolves into a microcrystalline form. The term is typically associated with silicon films in optical applications such as solar cells. Applications Silicon sol ...
, and heterogeneously
microcrystalline A microcrystalline material is a crystallized substance or rock that contains small crystals visible only through microscopic examination. There is little agreement on the range of crystal sizes that should be regarded as microcrystalline, but th ...
tubes, crusts, slags, and vesicular masses. Fulgurites are homologous to Lichtenberg figures, which are the branching patterns produced on surfaces of insulators during
dielectric breakdown Electrical breakdown or dielectric breakdown is a process that occurs when an electrical insulating material, subjected to a high enough voltage, suddenly becomes an electrical conductor and electric current flows through it. All insulating mate ...
by high-voltage discharges, such as lightning. Fulgurites are indicative of
thunderstorm A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorms are some ...
s; the distribution of fulgurites can hint at patterns of lightning strikes. Sponholz et al. (1993) studied fulgurite distributions along a north–south cross section in the south central Saharan Desert (
Niger ) , official_languages = , languages_type = National languages By examining the outcrops in which the fulgurite samples were found, Sponholz et al. (1993) could provide a relative date for the minerals. The fulgurite samples dated back approximately 15,000 years to the mid to upper
Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togeth ...
. This finding was in agreement with the
paleosol In the geosciences, paleosol (''palaeosol'' in Great Britain and Australia) is an ancient soil that formed in the past. The precise definition of the term in geology and paleontology is slightly different from its use in soil science. In geolo ...
s of the region, as this period of the Holocene was particularly wet. A wetter climate would suggest that the propensity for thunderstorms was probably elevated, which would result in larger concentrations of fulgurite. These results pointed to the fact that the climate with which the fulgurite was formed was significantly different from the present climate because the current climate of the Saharan Desert is
arid A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic. Most ...
. The approximate age of the fulgurite was determined using thermoluminescence (TL). Quartz sands can be used to measure the amount of radiation exposure, so if the temperature at which the fulgurite was formed is known, one could determine the relative age of the mineral by examining the doses of radiation involved in the process. Fulgurites also contain air bubbles. Given that the formation of fulgurite generally takes only about one second, and the process involved in the creation of fulgurite involves several chemical reactions, it is relatively easy to trap gases, such as , within the vesicles. These gases can be trapped for millions of years. Studies have shown that the gases within these bubbles can indicate the soil characteristics during the formation of the fulgurite material, which hint at the paleoclimate. Since fulgurite is almost entirely composed of
silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...
with trace amounts of
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...
and
magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
, an approximation of the total amount of organic carbon associated with that lightning strike can be made to calculate a
carbon-to-nitrogen ratio A carbon-to-nitrogen ratio (C/N ratio or C:N ratio) is a ratio of the mass of carbon to the mass of nitrogen in organic residues. It can, amongst other things, be used in analysing sediments and soil including soil organic matter and soil amendm ...
to determine the paleoenvironment.


Paleomagnetism

When geologists study paleoclimate, an important factor to examine is the magnetic field characteristics of rock types to determine not only deviations of Earth's past magnetic field, but also to study possible
tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents ...
activity that might suggest certain climate regimes. Evidence of lightning activity can often be found in the
paleomagnetic Paleomagnetism (or palaeomagnetismsee ), is the study of magnetic fields recorded in rocks, sediment, or archeological materials. Geophysicists who specialize in paleomagnetism are called ''paleomagnetists.'' Certain magnetic minerals in roc ...
record. Lightning strikes are the result of tremendous charge buildup in clouds. This excess charge is transferred to the ground via lightning channels, which carry a strong electric current. Because of the intensity of this electric current, when lightning hits the ground, it can produce a strong, albeit brief, magnetic field. Thus, as the electric current travels through soils, rocks, plant roots, etc., it locks a unique magnetic signature within these materials through a process known as lightning-induced remanent magnetization (LIRM). Evidence of LIRM is manifested in concentric magnetic field lines surrounding the location of the lightning strike point. LIRM anomalies normally occur close to the location of the lightning strike, usually encapsulated within several meters of the point of contact. The anomalies are generally linear or radial, which, just like actual lightning channels, branch out from a central point. It is possible to determine the intensity of the electric current from a lightning strike by examining the LIRM signatures. Since rocks and soils already have some preexisting magnetic field, the intensity of the electric current can be determined by examining the change between the "natural" magnetic field and the magnetic field induced by the lightning current, which generally acts parallel to the direction of the lightning channel. Another characteristic feature of an LIRM anomaly compared to other magnetic anomalies is that the electric current intensity is generally stronger. However, some have suggested that the anomalies, like other characteristics in the geologic record, might fade over time as the magnetic field redistributes. LIRM anomalies can often be problematic when examining the magnetic characteristics of rock types. LIRM anomalies can disguise the
natural remanent magnetization Natural remanent magnetization (NRM) is the permanent magnetism of a rock or sediment. This preserves a record of the Earth's magnetic field at the time the mineral was laid down as sediment or crystallized in magma and also the tectonic movement o ...
(NRM) of the rocks in question because the subsequent magnetization caused by the lightning strike reconfigures the magnetic record. While investigating the soil attributes at the 30-30 Winchester archeological site in northeastern Wyoming to discern the daily activities of prehistoric people that had once occupied that region, David Maki noticed peculiar anomalies in the magnetic record that did not match the circular magnetic remnant features of the ovens used by these prehistoric groups for cooking and pottery. The LIRM anomaly was significantly bigger than the other magnetic anomalies and formed a dendritic structure. To test the validity of the assertion that the magnetic anomaly was indeed the result of lightning and not another process, Maki (2005) tested the soil samples against known standards indicative of LIRM anomalies developed by Dunlop et al. (1984), Wasilewski and Kletetschka (1999), and Verrier and Rochette (2002). These standards include, but are not limited to: 1) Average REM (ratio between natural remanent magnetization to a laboratory standard value) greater than 0.2, and 2) Average Koenigsberger ratio (ratio between natural remanent magnetization and the natural field created by Earth's magnetic field). The findings indicated the evidence of LIRM at the archaeological site. LIRM anomalies also complicated the determination of the relative location of the poles during the late
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
from the magnetic field record of basaltic lava flows in
Mongolia Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 million, ...
. The presence of LIRM-affected rocks was determined when calculated
Koenigsberger ratio The Koenigsberger ratio is the proportion of remanent magnetization relative to induced magnetization in natural rocks. It was first described by . It is a dimensionless parameter often used in geophysical exploration to describe the magnetic chara ...
s were drastically higher than other magnetic signatures in the region.


References


External links

{{Commons category, Fulgurites
The Bibliography of Fulgurites
Lightning Historical geology Archaeological science