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 inves ...

geoarchaeology Geoarchaeology is a multi-disciplinary approach which uses the techniques and subject matter of geography, geology, geophysics and other Earth sciences to examine topics which inform archaeological knowledge and thought. Geoarchaeologists study ...

, 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, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...

quartz sand 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 form ...

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 Rock most often refers to: * Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids * Rock music, a genre of popular music Rock or Rocks may also refer to: Places United Kingdom * Rock, Caerphilly, a location in Wales ...

biomass Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...

, 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 convec ...

. Since lightning channels carry an

electric current An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The moving pa ...

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 early Earth is loosely defined as Earth in its first one billion years, or gigayear (Ga, 109y). The “early Earth” encompasses approximately the first gigayear in the evolution of our planet, from its initial formation in the young Solar Sy ...

(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, an ...

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 An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...

. 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 Eart ...

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 wel ...

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 was ...

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 d ...

, 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

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,

, and

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 de ...

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 am ...

s, a necessary element for the building blocks of living organisms.

Volcanic lightning on early Earth

The actual composition of the atmosphere of the

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 someti ...

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

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 Hydrogen cyanide, sometimes called prussic acid, is a chemical compound with the formula HCN and structure . It is a colorless, extremely poisonous, and flammable liquid that boils slightly above room temperature, at . HCN is produced on an ...

(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

nitrate Nitrate is a polyatomic ion A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zer ...

s and

, 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 molecule i ...

occurs, forming nitrogen-oxide (NO_x) 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 fuel A fossil fuel is a hydrocarbon-containing material formed naturally in the Earth's crust from the remains of dead plants and animals that is extracted and burned as a fuel. The main fossil fuels are coal, oil, and natural gas. Fossil fuels m ...

s. 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 someti ...

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 exchan ...

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 c ...

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 Earth's atmosphere, atmosphere of the Earth. Carbon is the main component of biological compounds as well as ...

, 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 Negative feedback (or balancing feedback) occurs when some function (Mathematics), function of the output of a system, process, or mechanism is feedback, fed back in a manner that tends to reduce the fluctuations in the output, whether caused by ...

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

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 A conceptual model is a representation of a system. It consists of concepts used to help people knowledge, know, understanding, understand, or simulation, simulate a subject the model represents. In contrast, physical models are physical object su ...

, 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 transpar ...

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 Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when humidi ...

from oceans would promote enhanced

. As a result of more numerous lightning strikes,

would deposit more biologically useful forms of nitrogen into various

s, encouraging

. Impacts on primary production would affect the

, leading to a reduction in atmospheric carbon dioxide. A reduction in atmospheric carbon dioxide would result in a negative feedback, or cooling, of the

. 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 Anthropogenic ("human" + "generating") is an adjective that may refer to: * Anthropogeny, the study of the origins of humanity Counterintuitively, anthropogenic may also refer to things that have been generated by humans, as follows: * Human im ...

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 which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

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

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 electric charge, electrically charged regions, both in the atmosphere or with one on the land, ground, temporarily neutralize themselves, causing the instantaneous ...

") 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 A mineraloid is a naturally occurring mineral-like substance that does not demonstrate crystallinity. Mineraloids possess chemical compositions that vary beyond the generally accepted ranges for specific minerals. For example, obsidian is an amor ...

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 one ...

-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 form ...

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 of s ...

, mixed

, 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 sola ...

, 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 the ...

tubes, crusts,

slag Slag is a by-product of smelting (pyrometallurgical) ores and used metals. Broadly, it can be classified as ferrous (by-products of processing iron and steel), ferroalloy (by-product of ferroalloy production) or non-ferrous/base metals (by-prod ...

s, and vesicular masses. Fulgurites are homologous to

Lichtenberg figure A Lichtenberg figure (German ''Lichtenberg-Figuren''), or Lichtenberg dust figure, is a branching electric discharge that sometimes appears on the surface or in the interior of insulating materials. Lichtenberg figures are often associated wit ...

s, 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

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 , photo = Sahara real color.jpg , photo_caption = The Sahara taken by Apollo 17 astronauts, 1972 , map = , map_image = , location = , country = , country1 = , ...

(

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 togethe ...

. 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 ar ...

. The approximate age of the fulgurite was determined using

thermoluminescence Thermoluminescence is a form of luminescence that is exhibited by certain crystalline materials, such as some minerals, when previously absorbed energy from electromagnetic radiation or other ionizing radiation is re-emitted as light upon he ...

(TL). Quartz sands can be used to measure the amount of

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...

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 Paleoclimatology (British spelling, palaeoclimatology) is the study of climates for which direct measurements were not taken. As instrumental records only span a tiny part of Earth's history, the reconstruction of ancient climate is important to ...

. Since fulgurite is almost entirely composed of

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 to ...

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 amendmen ...

to determine the paleoenvironment.

Paleomagnetism

When geologists study

, 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 k ...

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 rock ...

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

. 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 of ...

(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 th ...

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