Sources
- Aitken, M.J. (1990). Science-based Dating in Archaeology. London: Longman. ISBN 978-0-582-49309-4.
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Before Present (BP) or "years before present (YBP)" is a time scale used mainly in archaeology, geology, and other scientific disciplines to specify when events occurred relative to the origin of practical radiocarbon dating in the 1950s. Because the "present" time changes, standard practice is to use 1 January 1950 as the commencement date (epoch) of the age scale, with 1950 being labelled as the "standard year". The abbreviation "BP" has been interpreted retrospectively as "Before Physics", [1] [2] which refers to the time before nuclear weapons testing artificially altered the proportion of the carbon isotopes in the atmosphere, which scientists must account for. [3] [4]
In a convention that is not always observed, many sources restrict the use of BP dates to those produced with radiocarbon dating; the alternative notation "RCYBP" stands for the explicit "radio carbon years before present".
The BP scale is sometimes used for dates established by means other than radiocarbon dating, such as stratigraphy. [5] [6] This usage differs from the recommendation by van der Plicht & Hogg, [7] followed by the Quaternary Science Reviews , [8] [9] both of which requested that publications should use the unit "a" (for "annum", Latin for "year") and reserve the term "BP" for radiocarbon estimations.
Some archaeologists use the lowercase letters bp, bc and ad as terminology for uncalibrated dates for these eras. [10]
The Centre for Ice and Climate at the University of Copenhagen instead uses the unambiguous "b2k", for "years before 2000 AD", often in combination with the Greenland Ice Core Chronology 2005 (GICC05) time scale. [11]
Some authors who use the YBP dating format also use "YAP" ("years after present") to denote years after 1950. [12]
SI prefix multipliers may be used to express larger periods of time, e.g. ka BP (thousand years BP), Ma BP (million years BP) and many others. [13]
Radiocarbon dating was first used in 1949. [14] [15] Beginning in 1954, metrologists established 1950 as the origin year for the BP scale for use with radiocarbon dating, using a 1950-based reference sample of oxalic acid. According to scientist A. Currie Lloyd:
The problem was tackled by the international radiocarbon community in the late 1950s, in cooperation with the U.S. National Bureau of Standards. A large quantity of contemporary oxalic acid dihydrate was prepared as NBS Standard Reference Material (SRM) 4990B. Its 14C concentration was about 5% above what was believed to be the natural level, so the standard for radiocarbon dating was defined as 0.95 times the 14C concentration of this material, adjusted to a 13C reference value of −19 per mil (PDB). This value is defined as "modern carbon" referenced to AD 1950. Radiocarbon measurements are compared to this modern carbon value, and expressed as "fraction of modern" (fM). "Radiocarbon ages" are calculated from fM using the exponential decay relation and the "Libby half-life" 5568 a. The ages are expressed in years before present (BP) where "present" is defined as AD 1950. [16]
The year 1950 was chosen because it was the standard astronomical epoch at that time.[ citation needed ] It also marked [3] the publication of the first radiocarbon dates in December 1949, [17] and 1950 also antedates large-scale atmospheric testing of nuclear weapons, which altered the global ratio of carbon-14 to carbon-12. [18]
Dates determined using radiocarbon dating come as two kinds: uncalibrated (also called Libby or raw) and calibrated (also called Cambridge) dates. [19] Uncalibrated radiocarbon dates should be clearly noted as such by "uncalibrated years BP", because they are not identical to calendar dates. This has to do with the fact that the level of atmospheric radiocarbon (carbon-14 or 14C) has not been strictly constant during the span of time that can be radiocarbon-dated. Uncalibrated radiocarbon ages can be converted to calendar dates by calibration curves based on comparison of raw radiocarbon dates of samples independently dated by other methods, such as dendrochronology (dating based on tree growth-rings) and stratigraphy (dating based on sediment layers in mud or sedimentary rock). Such calibrated dates are expressed as cal BP, where "cal" indicates "calibrated years", or "calendar years", before 1950.
Many scholarly and scientific journals require that published calibrated results be accompanied by the name (standard codes are used) of the laboratory concerned, and other information such as confidence levels, because of differences between the methods used by different laboratories and changes in calibrating methods.
Conversion from Gregorian calendar years to Before Present years is by starting with the 1950-01-01 epoch of the Gregorian calendar and increasing the BP year count with each year into the past from that Gregorian date.
For example, 1000 BP corresponds to 950 AD, 1949 BP corresponds to 1 AD, 1950 BP corresponds to 1 BC, 2000 BP corresponds to 51 BC.
| Gregorian year | BP year | Event |
|---|---|---|
| 9701 BC | 11650 BP | End of the Pleistocene and beginning of the Holocene epoch [20] |
| 4714 BC | 6663 BP | Epoch of the Julian day system: Julian day 0 starts at Greenwich noon on January 1, 4713 BC of the proleptic Julian calendar, which is November 24, 4714 BC in the proleptic Gregorian calendar [21] : 10 |
| 2251 BC | 4200 BP | Beginning of the Meghalayan age, the current and latest of the three stages in the Holocene era. [22] [23] |
| 45 BC | 1994 BP | Introduction of the Julian calendar |
| 1 BC | 1950 BP | Year zero in ISO 8601 |
| AD 1 | 1949 BP | Beginning of the Common Era and Anno Domini, from the estimate by Dionysius of the Incarnation of Jesus |
| 1582 | 368 BP | Introduction of the Gregorian calendar [21] : 47 |
| 1950 | 0000 AP | Epoch of the Before Present dating scheme [24] : 190 |
| 2024 | 0074 AP | Current year |
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Radiocarbon dating is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon.
Dendrochronology is the scientific method of dating tree rings to the exact year they were formed in a tree. As well as dating them, this can give data for dendroclimatology, the study of climate and atmospheric conditions during different periods in history from the wood of old trees. Dendrochronology derives from the Ancient Greek dendron, meaning "tree", khronos, meaning "time", and -logia, "the study of".
Carbon-14, C-14, 14C or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic matter is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues (1949) to date archaeological, geological and hydrogeological samples. Carbon-14 was discovered on February 27, 1940, by Martin Kamen and Sam Ruben at the University of California Radiation Laboratory in Berkeley, California. Its existence had been suggested by Franz Kurie in 1934.
Willard Frank Libby was an American physical chemist noted for his role in the 1949 development of radiocarbon dating, a process which revolutionized archaeology and palaeontology. For his contributions to the team that developed this process, Libby was awarded the Nobel Prize in Chemistry in 1960.
The Huelmo–Mascardi Cold Reversal (HMCR) is a cooling event in South America between 11,400 and 10,200 14C years BP. This cooling began about 550 years before the Younger Dryas cooling in the Northern Hemisphere, and both periods ended at about the same time.
Absolute dating is the process of determining an age on a specified chronology in archaeology and geology. Some scientists prefer the terms chronometric or calendar dating, as use of the word "absolute" implies an unwarranted certainty of accuracy. Absolute dating provides a numerical age or range, in contrast with relative dating, which places events in order without any measure of the age between events.
The Holocene calendar, also known as the Holocene Era or Human Era (HE), is a year numbering system that adds exactly 10,000 years to the currently dominant numbering scheme, placing its first year near the beginning of the Holocene geological epoch and the Neolithic Revolution, when humans shifted from a hunter-gatherer lifestyle to agriculture and fixed settlements. The current year by the Gregorian calendar, AD 2024, is 12024 HE in the Holocene calendar. The HE scheme was first proposed by Cesare Emiliani in 1993, though similar proposals to start a new calendar at the same date had been put forward decades earlier.
Laacher See, also known as Lake Laach or Laach Lake, is a volcanic caldera lake with a diameter of 2 km (1.2 mi) in Rhineland-Palatinate, Germany, about 24 km (15 mi) northwest of Koblenz, 37 km (23 mi) south of Bonn, and 8 km (5.0 mi) west of Andernach. It is in the Eifel mountain range, and is part of the East Eifel volcanic field within the larger Volcanic Eifel. The lake was formed by a Plinian eruption approximately 13,000 years BP with a Volcanic Explosivity Index (VEI) of 6, on the same scale as the Pinatubo eruption of 1991. The volcanic discharge observable as mofettas on the southeastern shore of the lake is a sign of dormant volcanism.
The Baltic Ice Lake is a name given by geologists to a freshwater lake that evolved in the Baltic Sea basin as glaciers retreated from that region at the end of the last ice age. The lake's existence was first understood in 1894. The lake existed between about 16,000 and 11,700 years ago with well defined evidence from the warming of the Bølling–Allerød Interstadial to the period of cooling called the Younger Dryas before the Holocene, the onset of which is close in time to the end of the ice lake. The lake drained into the raising world ocean on two occasions and when water levels became the same on the second, with a sea level passage in the Billingen region of southern Sweden, it became the Yoldia Sea.
Wiggle matching, also known as carbon–14 wiggle-match dating (WMD) is a dating method that uses the non-linear relationship between 14C age and calendar age to match the shape of a series of closely sequentially spaced 14C dates with the 14C calibration curve. A numerical approach to WMD allows one to assess the precision of WMD chronologies. The method has both advantages and limitations for the calibration of individual dates. High-precision chronologies are needed for studies of rapid climate changes. Andrew Millard refers to wiggle matching as a way of dealing with the flat portion of the carbon 14 calibration graph that is known as the Hallstatt plateau, named after the Hallstatt culture period in central Europe with which it coincides.
The Younger Dryas impact hypothesis (YDIH) proposes that the onset of the Younger Dryas (YD) cool period (stadial) at the end of the Last Glacial Period, around 12,900 years ago was the result of some kind of cosmic event with specific details varying between publications. The hypothesis is widely rejected by relevant experts. It is influenced by creationism, and has been compared to cold fusion by its critics due to the lack of reproducibility of results. It is an alternative to the long-standing and widely accepted explanation that the Younger Dryas was caused by a significant reduction in, or shutdown of the North Atlantic Conveyor due to a sudden influx of freshwater from Lake Agassiz and deglaciation in North America.
The Hatepe eruption, named for the Hatepe Plinian pumice tephra layer, sometimes referred to as the Taupō eruption or Horomatangi Reef Unit Y eruption, is dated to 232 CE ± 10 and was Taupō Volcano's most recent major eruption. It is thought to be New Zealand's largest eruption within the last 20,000 years. The eruption ejected some 45–105 km3 (11–25 cu mi) of bulk tephra, of which just over 30 km3 (7.2 cu mi) was ejected in approximately 6–7 minutes. This makes it one of the largest eruptions in the last 5,000 years, comparable to the Minoan eruption in the 2nd millennium BCE, the 946 eruption of Paektu Mountain, the 1257 eruption of Mount Samalas, and the 1815 eruption of Mount Tambora.
Carbon dating the Dead Sea Scrolls refers to a series of radiocarbon dating tests performed on the Dead Sea Scrolls, first by the AMS lab of the Zurich Institute of Technology in 1991 and then by the AMS Facility at the University of Arizona in Tucson in 1994–95. There was also a historical test of a piece of linen performed in 1946 by Willard Libby, the inventor of the dating method.
The Hallstatt plateau or the first millennium BC radiocarbon disaster, as it is called by some archaeologists and chronologists, is a term used in archaeology that refers to a consistently flat area on graphs that plot radiocarbon dating against calendar dates. When applied to the Scythian epoch in Eurasia, radiocarbon dates of around 2450 BP, so c. 500 BC, always calibrate to c. 800–400 BC, no matter the measurement precision. The radiocarbon dating method is hampered by this large plateau on the calibration curve in a critical period of human technological development. Just before and after the plateau, radiocarbon calibration gives precise dates. However, during the plateau the calendar date estimates obtained when calibrating single radiocarbon measurements are very broad and cover the entire duration of the plateau. Only techniques like wiggle matching can yield more precise calendar dates during this period. The plateau is named after the Hallstatt culture period in central Europe with which it coincides.
Christopher Bronk Ramsey is a British physicist, mathematician and specialist in radiocarbon dating. He is a professor at the University of Oxford and was the Director of the Research Laboratory for Archaeology and the History of Art (RLAHA) from 2014 until 2019. He is a member of Merton College, Oxford and a Bodley Fellow. His doctorate, completed in 1987, included the first successful implementation of carbon dioxide gas as a target for radiocarbon dating via accelerator mass spectrometry.
Minze Stuiver was a Dutch geochemist who was at the forefront of geoscience research from the 1960s until his retirement in 1998. He helped transform radiocarbon dating from a simple tool for archaeology and geology to a precise technique with applications in solar physics, oceanography, geochemistry, and carbon dynamics. Minze Stuiver's research encompassed the use of radiocarbon (14C) to understand solar cycles and radiocarbon production, ocean circulation, lake carbon dynamics and archaeology as well as the use of stable isotopes to document past climate changes.
Radiocarbon dating measurements produce ages in "radiocarbon years", which must be converted to calendar ages by a process called calibration. Calibration is needed because the atmospheric 14
C/12
C ratio, which is a key element in calculating radiocarbon ages, has not been constant historically.
The bomb pulse is the sudden increase of carbon-14 (14C) in the Earth's atmosphere due to the hundreds of above-ground nuclear bombs tests that started in 1945 and intensified after 1950 until 1963, when the Limited Test Ban Treaty was signed by the United States, the Soviet Union and the United Kingdom. These hundreds of blasts were followed by a doubling of the relative concentration of 14C in the atmosphere.
The Homeric Minimum is a grand solar minimum that started about 2,800 years ago and lasted around 200 years. It appears to coincide with, and have been the cause of, a phase of climate change at that time, which involved a wetter Western Europe and drier eastern Europe. This had far-reaching effects on human civilization, some of which may be recorded in Greek mythology and the Old Testament.
Paula Jo Reimer is a radiocarbon and archaeological scientist. Reimer is the former director of the 14Chrono Centre for Climate, the Environment, and Chronology at Queen's University Belfast.
