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Geochronology is the science of determining the age of rocks, fossils, and sediments, within a certain degree of uncertainty inherent to the method used. A variety of dating methods are used by geologists to achieve this,^[1][2] and schemes of classification and terminology have been proposed.^[3] The approach of using several methods is preferred for best results (by consilience).

Geochronology is different in application from biostratigraphy, which is the science of assigning sedimentary rocks to a known geological period via describing, cataloguing and comparing fossil floral and faunal assemblages. Biostratigraphy does not directly provide an absolute age determination of a rock, but merely places it within an interval of time at which that fossil assemblage is known to have coexisted. Both disciplines work together hand in hand however, to the point they share the same system of naming rock layers and the time spans utilized to classify layers within a strata.

The science of geochronology is the prime tool used in the discipline of chronostratigraphy, which attempts to derive absolute age dates for all fossil assemblages and determine the geologic history of the Earth and extraterrestrial bodies.

Dating methods[link]

Radiometric dating[link]

By measuring the amount of radioactive decay of a radioactive isotope with a known half-life, geologists can establish the absolute age of the parent material. A number of radioactive isotopes are used for this purpose, and depending on the rate of decay, are used for dating different geological periods. More slowly decaying isotopes are useful for longer periods of time, but less accurate in absolute years. With the exception of the radiocarbon method, most of these techniques are actually based on measuring an increase in the abundance of a radiogenic isotope, which is the decay-product of the radioactive parent isotope.^[5][6][7] Two or more radiometric methods can be used in concert to achieve more robust results.^[8] Most radiometric methods are suitable for geological time only, but some such as the radiocarbon method and the ⁴⁰Ar/³⁹Ar dating method can be extended into the time of early human life^[9] and into recorded history.^[10]

Some of the commonly-used techniques are:

• Radiocarbon dating. This technique measures the decay of carbon-14 in organic material and can be best applied to samples younger than about 60,000 years.^[11]
• Uranium-lead dating. This technique measures the ratio of two lead isotopes (lead-206 and lead-207) to the amount of uranium in a mineral or rock. Often applied to the trace mineral zircon in igneous rocks, this method is one of the two most commonly used (along with argon-argon dating) for geologic dating. Uranium-lead dating is applied to samples older than about 1 million years.
• Uranium-thorium dating. This technique is used to date speleothems, corals, carbonates, and fossil bones. Its range is from a few years to about 700,000 years.
• Potassium-argon dating and argon-argon dating. These techniques date metamorphic, igneous and volcanic rocks. They are also used to date volcanic ash layers within or overlying paleoanthropologic sites. The younger limit of the argon-argon method is a few thousand years.
• Electron spin resonance dating (ESR dating)

Cosmogenic Nuclide Geochronology[link]

A series of related techniques for determining the age at which a geomorphic surface was created (exposure dating), or at which formerly surficial materials were buried (burial dating). Exposure dating uses the concentration of exotic nuclides (e.g. ¹⁰Be, ²⁶Al, ³⁶Cl) produced by cosmic rays interacting with Earth materials as a proxy for the age at which a surface, such as an alluvial fan, was created. Burial dating uses the differential radioactive decay of 2 cosmogenic elements as a proxy for the age at which a sediment was screened by burial from further cosmic rays exposure.

Luminescence dating[link]

Luminescence dating techniques observe 'light' emitted from materials such as quartz, diamond, feldspar, and calcite. Many types of luminescence techniques are utilized in geology, including optically stimulated luminescence (OSL), cathodoluminescence (CL), and thermoluminescence (TL). Thermoluminescence and optically stimulated luminescence are used in archaeology to date 'fired' objects such as pottery or cooking stones, and can be used to observe sand migration.

Incremental dating[link]

Incremental dating techniques allow the construction of year-by-year annual chronologies, which can be fixed (i.e. linked to the present day and thus calendar or sidereal time) or floating.

• Dendrochronology
• Ice cores
• Lichenometry
• Varves

Magnetostratigraphy[link]

Magnetostratigraphy determines age from the pattern of magnetic polarity zones in a series of bedded sedimentary and/or volcanic rocks by comparison to the magnetic polarity timescale. The polarity timescale has been previously determined by dating of seafloor magnetic anomalies, radiometrically dating volcanic rocks within magnetostratigraphic sections, and astronomically dating magnetostratigraphic sections.

Correlation of marker horizons[link]

Tephra horizons in south-central Iceland. The thick and light-to-dark coloured layer at the height of the volcanologists hands is a marker horizon of rhyolitic-to-basaltic tephra from Hekla.

Marker horizons are stratigraphic units of the same age and of such distinctive composition and appearance, that despite their presence in different geographic sites, there is certainty about their age-equivalence. Fossil faunal and floral assemblages, both marine and terrestrial, make for distinctive marker horizons.^[12] Tephrochronology is a method for geochemical correlation of unknown volcanic ash (tephra) to geochemically-fingerprinted, dated tephra. Tephra is also often used as a dating tool in archaeology, since the dates of some eruptions are well-established.

Differences between chronostratigraphy and geochronology[link]

It is important not to confuse geochronologic and chronostratigraphic units.^[13] Geochronological units are periods of time, thus it is correct to say that Tyrannosaurus rex lived during the Late Cretaceous Epoch.^[14] Chronostratigraphic units are geological material, so it is also correct to say that fossils of the genus Tyrannosaurus have been found in the Upper Cretaceous Series.^[15] In the same way, it is entirely possible to go and visit an Upper Cretaceous Series deposit - such as the Hell Creek deposit where the Tyrannosaurus fossils were found - but it is naturally impossible to visit the Late Cretaceous Epoch as that is a period of time.

See also[link]

• Age of the Earth
• List of geochronologic names
• Thermochronology
• Closure temperature
• Arthur Holmes
• Fritz Houtermans
• Alfred O. C. Nier
• Thomas Edvard Krogh

References[link]

Further reading[link]

• Lowe, J.J., and Walker, M.J.C. (1997), Reconstructing Quaternary Environments (2nd edition). Longman publishing ISBN 0-582-10166-2
• Smart, P.L., and Frances, P.D. (1991), Quaternary dating methods - a user's guide. Quaternary Research Association Technical Guide No.4 ISBN 0-907780-08-3
• Geochronology bibliography Talk:Origins Archive

External links[link]

• International Commission on Stratigraphy

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Clifford Lee "Cliff" Burton (February 10, 1962 – September 27, 1986) was an American musician, best known as the bass guitarist for the American heavy metal band Metallica.

Burton joined the band in 1982 and performed on its debut studio album, Kill 'Em All. He performed on two more Metallica albums, Ride the Lightning and Master of Puppets, both of which met with major commercial and critical success. Burton was known for his "lead bass" approach, in which the bass played a melodic and soloist role, in addition to holding down the harmonic and rhythmic foundation of the band.

On September 27, 1986, Burton died when the band's tour bus over-turned in rural southern Sweden. Burton was posthumously inducted into the Rock and Roll Hall of Fame with Metallica on April 4, 2009.

Early Life[link]

Burton was born on February 10, 1962, in Castro Valley, California to Jan and Ray Burton. He had two elder siblings, Scott and Connie. Burton's interest in music began when his father introduced him to classical music and he began taking piano lessons. In his teenage years, Burton had an interest in rock, classical and eventually heavy metal. He began playing the bass at age 13, after the death of his brother. His parents quoted him as saying, "I'm going to be the best bassist for my brother."^[1] He practiced up to six hours per day (even after he joined Metallica). Along with classical and jazz, Burton's other early influences varied from southern rock, country and blues.^[2]

Career[link]

While still a student at Castro Valley High School, Burton formed his first band called EZ-Street. The band took its name from a Bay Area topless bar. Other members of EZ Street included future Faith No More guitarist "Big" Jim Martin and future Faith No More and Ozzy Osbourne drummer Mike Bordin. Burton and Martin continued their musical collaboration after becoming students at Chabot College in Hayward, California. Their second band, Agents of Misfortune, entered the Hayward Area Recreation Department's Battle of the Bands contest in 1981. Their audition was recorded on video and features some of the earliest footage of Burton's trademark playing style. The video also shows Burton playing parts of what would soon be two Metallica songs: his signature bass solo, "(Anesthesia) Pulling Teeth", and the chromatic intro to "For Whom the Bell Tolls".^[2] Burton joined his first major band, Trauma, in 1982. Burton recorded the track "Such a Shame" with the band on the second Metal Massacre compilation.

In 1982, Trauma traveled to Los Angeles to perform at the Whisky a Go Go.^[2] Among those in attendance were James Hetfield and Lars Ulrich, both members of Metallica, which had formed the previous year. Upon hearing, as Hetfield described it, "this amazing shredding" (which later became "(Anesthesia) Pulling Teeth"), the two went in search of what they thought was an amazing guitar player. When they learned that what they had heard was a bass solo by Burton, they decided to recruit him for their own band. They asked him to replace departed bassist Ron McGovney, and since Burton thought that Trauma was "starting to get a little commercial",^[3] he agreed. The idea of having to move to Los Angeles did not sit well with him, and said he would join only if the band would relocate from Los Angeles to his native San Francisco Bay Area.^[2] Metallica, eager to have Burton in the band, left their origin of Los Angeles to make a home in El Cerrito,^[4] a town located across the bay from San Francisco.

Burton's first recording with Metallica was the Megaforce demo. A demo tape the band had made prior to Burton's joining, No Life 'til Leather, managed to come into the hands of John Zazula, owner of Megaforce Records.^[5] The band relocated to Old Bridge, New Jersey and quickly secured a recording contract with Zazula's label.^[5] Its debut album, Kill 'Em All, features Burton's famous solo piece, "(Anesthesia) Pulling Teeth", which showcased his use of effects, such as a wah-wah pedal.

Metallica's first album, Kill 'Em All, was originally titled Metal Up Your Ass, but the music censors didn't like the title and forced the band to change it. After the band learned of the change, Cliff said "Just kill 'em all, man," ^[6] which gave the band members an idea for the new title. Metallica's debut album was released in 1983.

The band's second studio album, Ride the Lightning, showcased the band's increasing musical growth.^[7] Burton's songwriting abilities were growing, and he received credit on six of the album's eight songs.^[8] Burton's playing style and use of effects is showcased on two tracks: the chromatic intro to "For Whom the Bell Tolls", and the "lead bass" on "The Call of Ktulu".

The increase of musicianship on Ride the Lightning caught the attention of major record labels.^[5] Metallica was signed to Elektra Records, and began working on its third album, Master of Puppets, which is considered by most critics to be a landmark album in both thrash and the whole of metal.^[9] Burton is featured heavily on a number of tracks, most notably the instrumental "Orion", which again featured Burton's lead bass playing style. The album also contained Burton's favorite Metallica song "Master of Puppets".^[10] Master of Puppets was the band's commercial breakthrough,^[11] but it would be Burton's final album with Metallica.

Burton's final performance was in Stockholm, Sweden, at the Solnahallen Arena on September 26, 1986.^[12]

Death[link]

Memorial stone near the crash site, next to Master of Puppets CD.

During the European leg of the Damage Inc. tour in support of Master of Puppets, the band complained that the sleeping cubicles on their tour bus were unsatisfactory and uncomfortable. To decide who received pick of the bunks, Kirk Hammett and Burton drew cards.^[13] On the evening of September 26, 1986, Burton won the game with an Ace of Spades, thereby getting the first choice of bunk and pointed at Hammett and exclaimed "I want your bunk!" Hammett replied "Fine, take my bunk, I'll sleep up front, it's probably better up there anyway". Burton was sleeping shortly before 7 am on September 27 when, according to the driver, the bus skidded off the road (the E4, 2 miles north of Ljungby),^[14] and flipped into the grass in Ljungby Municipality, near Dörarp in rural southern Sweden.^[15] Burton was thrown through the window of the bus, which fell on top of him. They tried to save him and managed to lift the bus up a little using a crane. But, before they could retrieve him, the weight of the bus became too much and the bus slipped off the crane and landed on the ground again.

James Hetfield later stated that he first believed the bus flipped because the driver was drunk. Hetfield stated that he walked long distances down the road looking for black ice and found none. Local freelance photographer Lennart Wennberg, who attended the crash scene the following morning, later asked in an interview about the likelihood that black ice caused the accident, said it was 'out of the question' because the road was dry and the temperature around two degrees Celsius (37 degrees Fahrenheit). This was confirmed by police who found no ice on the road. Ljungby detective Arne Pettersson was reported in a local newspaper to have said the tracks at the accident site were exactly like ones seen when drivers fall asleep at the wheel. However, the driver stated under oath that he had slept during the day and was fully rested; his testimony was confirmed by the driver of a second tour bus that was carrying the band's crew and equipment.^[14] The driver was determined not at fault for the accident and no charges were brought against him.^[16]

Legacy[link]

Burton was cremated and his ashes scattered at the Maxwell Ranch.^[13] At the ceremony, the song "Orion" was played. The lyrics "...cannot the Kingdom of Salvation take me home" from "To Live Is to Die" are written on Burton's memorial stone. Shortly after Burton's death, Jason Newsted from Flotsam and Jetsam became Metallica's new bassist; a position he held until January 2001.

A memorial for Burton in Ljungby, Sweden

The best-known non-Metallica tribute to Burton is the song "In My Darkest Hour" by thrash metal band Megadeth. According to Dave Mustaine, after hearing of Burton's death, he sat down and wrote the music for the song in one sitting. The lyrics, however, are unrelated to Burton's death. Mustaine was Metallica's lead guitarist in the early days and was a close friend of Burton at the time. Mustaine said that the dark atmosphere of the song was inspired by Burton's death.^[17]

On October 3, 2006, a memorial stone was unveiled in Sweden near the scene of the fatal crash. It is located by the parking lot to Gyllene Rasten.

Contemporary thrash metal band Anthrax dedicated its album Among the Living to him, as did Metal Church with The Dark.

On April 4, 2009, Burton was posthumously inducted into the Rock and Roll Hall of Fame, with the rest of Metallica. During the ceremony, the induction was accepted by his father, Ray Burton, who shared the stage with the band and mentioned that Cliff's mother was actually Metallica's biggest fan.

A biography, To Live Is to Die: The Life and Death of Metallica's Cliff Burton, written by Joel McIver, was published by Jawbone Press in June 2009. Hammett provided the book's foreword.^[18]

Discography[link]

References[link]

External links[link]

Biography portal

Wikimedia Commons has media related to: Cliff Burton

• Metallica.com - The Official Metallica Website
• Cliff In Our Minds memorial website
• Arron's Tribute To Cliff Burton