what is the younger dryas boundary

If you imagine the surface of the Earth as like a cake, the Younger Dryas

Boundary is the layer that was frosted onto its surface 12,800 years ago, subsequently covered by other layers over the millennia. What caused the Oldest Dryas?

Full Answer

What is the Younger Dryas boundary layer?

Multiple meteor air bursts and/or impacts are claimed to have produced the Younger Dryas (YD) boundary layer (YDB), depositing peak concentrations of platinum, high-temperature spherules, meltglass, and nanodiamonds, forming an isochronous datum at more than 50 sites across about 50 million km 2 of Earth 's surface.

What is the Younger Dryas (YD)?

The temperatures dropped massively entering into a near-glacial period where it was cold and windy and this is what is known as the Younger Dryas (YD).

When did the Younger Dryas end and the modern climate begin?

A second abrupt climatic warming event, approximately 11,600 years ago, marked the end of the Younger Dryas and the beginning of the Holocene Epoch (11,700 years ago to the present) and Earth ’s modern climate. In this second warming interval, average global temperatures increased by up to 10 °C (18 °F) in just a few decades.

What caused the Younger Dryas?

The current theory is that the Younger Dryas was caused by significant reduction or shutdown of the North Atlantic "Conveyor", which circulates warm tropical waters northward, in response to a sudden influx of fresh water from Lake Agassiz and deglaciation in North America.

What is the Younger Dryas and why is it important?

The Younger Dryas is a period significant to the study of the response of biota to abrupt climate change and to the study of how humans coped with such rapid changes.

What is the Younger Dryas interval?

Younger Dryas, also called Younger Dryas stadial, cool period between roughly 12,900 and 11,600 years ago that disrupted the prevailing warming trend occurring in the Northern Hemisphere at the end of the Pleistocene Epoch (which lasted from 2.6 million to 11,700 years ago).

What did the Younger Dryas event cause?

This climate event, called the Younger Dryas by scientists, marked the beginning of a decline in ice-age megafauna, such as mammoth and mastodon, eventually leading to extinction of more than 35 genera of animals across North America.

Are we in an ice age?

We are in an interglacial period right now. It began at the end of the last glacial period, about 10,000 years ago. Scientists are still working to understand what causes ice ages. One important factor is the amount of light Earth receives from the Sun.

Why is it called Younger Dryas?

This near-glacial period is called the Younger Dryas, named after a flower (Dryas octopetala) that grows in cold conditions and that became common in Europe during this time. The end of the Younger Dryas, about 11,500 years ago, was par- ticularly abrupt.

Will there be another ice age?

The onset of an ice age is related to changes in the Earth's tilt and orbit. The Earth is due for another ice age now but climate change makes it very unlikely.

How warm was Medieval Warm Period?

The Medieval Warm Period was approximately 1 °C warmer than present, and the Little Ice Age 0.6 °C cooler than present, in central Greenland.

What ended the last Ice Age?

New University of Melbourne research has revealed that ice ages over the last million years ended when the tilt angle of the Earth's axis was approaching higher values.

How long was the last ice age?

Striking during the time period known as the Pleistocene Epoch, this ice age started about 2.6 million years ago and lasted until roughly 11,000 years ago. Like all the others, the most recent ice age brought a series of glacial advances and retreats.

Was the Younger Dryas triggered by a flood?

It is widely believed that this cold event was triggered by a flood of fresh water that poured into the northern Atlantic (1) and disrupted the thermohaline ocean circulation (2).

What is the Younger Dryas quizlet?

- Younger Dryas is characterized by abrupt changes in climate. - oxygen isotope from the Greenland ice core shows an abrupt temperature drop 12,800 years ago, 1300 years of cool climate, and sudden warming 11,500 years ago (not just a single climatic event)

Will there be another ice age?

The onset of an ice age is related to changes in the Earth's tilt and orbit. The Earth is due for another ice age now but climate change makes it very unlikely.

Where did the Younger Dryas come from?

The first evidence of the Younger Dryas came from ice cores taken from European maritime environments dating to the late Pleistocene. The ice cores showed that the warming process produced abrupt wholesale melting of late Pleistocene glaciers. Subsequent examination of terrestrial plants and pollen in the cores indicated that forests were replaced by tundra vegetation during a cool period.

What was the Younger Dryas event?

After the period ended, an interval of rapid global warming increased average temperatures to levels comparable to those of the present day. The Younger Dryas was named after Dryas octopetala, a pale yellow wildflower of the rose family, typical of cold open Arctic environments. Younger Dryas event. The Younger Dryas event was characterized by ...

What was the ice sheet that formed during the Pleistocene era?

During the Pleistocene Epoch, extensive ice sheets and other glaciers formed repeatedly on large landmasses. The Younger Dryas, one of several very abrupt climatic changes that took place near the end of the late Pleistocene, was preceded by a sudden warming interval beginning approximately 14,700 years ago. This interval, the Bølling-Allerød interstadial, saw the rapid retreat of the immense Pleistocene ice sheets. A second abrupt climatic warming event, approximately 11,600 years ago, marked the end of the Younger Dryas and the beginning of the Holocene Epoch (11,700 years ago to the present) and Earth ’s modern climate. There is evidence that this warming was quite rapid; Greenland ice-core samples suggest that local temperatures increased by up to 10 °C (18 °F) in just a few decades.

How long did the Dryas period last?

Younger Dryas, also called Younger Dryas stadial, cool period between roughly 12,900 and 11,600 years ago that disrupted the prevailing warming trend occurring at the end of the Pleistocene Epoch (which lasted from 2.6 million to 11,700 years ago). The Younger Dryas was characterized by cooler average temperatures that returned parts ...

How much did the Younger Dryas warm?

The total warming at the end of the Younger Dryas was about 10 4 °C (18 7.2 °F). Radiocarbon dating of glacial moraines and measurements of oxygen isotopes in ice cores indicate that the cooling during the Younger Dryas occurred worldwide. Evidence of advancing continental ice sheets coincident with the Younger Dryas is reported from ...

What caused the sudden shutdown of the thermohaline circulation in the Atlantic basin?

For example, during the Younger Dryas event ( see below) a gradual increase in the release of fresh water to the North Atlantic Ocean led to an abrupt shutdown of the thermohaline circulation in the Atlantic basin. Abrupt climate shifts are of great societal concern, for any such shifts in…

How cold was Greenland during the Younger Dryas?

Isotope data from GISP2 suggests that Greenland was approximately 15 °C (27 °F) colder during the Younger Dryas than it is today and that the sudden warming that ended the Younger Dryas took about 40 to 50 years. The total warming at the end of the Younger Dryas was about 10 4 °C (18 7.2 °F).

What is the Younger Dryas Stadial?

The Younger Dryas Stadial is a time of extreme cold and tundra conditions which followed the Lateglacial Interstadial and immediately preceded the sudden warming at the onset of the present interglacial. Again, the Younger Dryas is a period whose fauna is largely known from radiocarbon dates on individual bones rather than from discrete assemblages. A site that would have been critical to a much better understanding of the fauna and environment of this time is Chelm's Combe Shelter, Cheddar, Somerset, but, sadly, this important locality was destroyed by quarrying.

Where are the Younger Dryas cold events?

South America is probably the continent where discussions about the presence or absence of a Younger Dryas cold event have been most lively. Most of these conflicting glacial, palynological, and paleoentomological records are from Chile and Argentina, but several records also exist from more northerly areas such as the central Andes and in the Amazon Basin ( Clapperton, 1993 ). Paleoclimatic interpretations of these data sets and the chronology of the records seem to have been the two main obstacles for finding a common Younger Dryas signal. The hitherto best dated series of South American cooling events come from two sites at 41° S in Chile and Argentina ( Hajdas et al., 2003) dated to ca. 11 500–10 200 14 C years BP (ca. 13 400–12 000 cal. years BP). This implies that any South American equivalent to the Younger Dryas overlapped half of the European Allerød warm period and half of the Younger Dryas cooling. It should, however, also be remembered that the data sets analyzed and discussed, were formed during a climatically very dynamic time period. Large differences should, therefore, be expected between the Amazon Basin at the Equator and Tierra del Fuego in the south, the Atlantic coast in the east, and the high Andes in the west. The debate was also fueled by reports of well-dated so-called Younger Dryas glacial advances in New Zealand ( Denton and Hendy, 1994) with mean 14 C ages of 11 000 14 C years BP. In light of the already existing knowledge that such ages predate the North Atlantic Younger Dryas cooling, it would have been more appropriate to regard these dates as evidence for ‘Allerød glacial advances in the Southern Hemisphere.’ Time is also needed to build-up glacier ice and form the moraines. The concept of pre-Younger Dryas glacial advances in New Zealand is now generally accepted ( Shulmeister et al., 2005 ), and detailed dating of a climate reversal in Kaipo bog, with an age of 13 600–12 600 cal. years BP ( Hajdas et al., 2006 ), shows that this cooling most likely triggered any glacial advances.

What caused the Younger Dryas?

Although the Younger Dryas was most likely triggered by changes in the North Atlantic, it would be surprising if this event was not felt by the climate system of the Southern Hemisphere; the large impact of the Younger Dryas on the Northern Hemisphere climate ought to have been propagated, in one way or another, into some of the driving mechanisms for the Southern Hemisphere climate system.

Where did the Dryas cooling occur?

A Younger Dryas cooling occurred along the northwest margin of North America (Kienast and McKay, 2001;

What are the climatic effects of the YD?

Climatic effects of the YD are geographically complex: areas close to the North Atlantic cooled dramatically but regions located farther away show reduced effects, and parts of North America actually warmed in response to increasing northern hemisphere insolation ( Berger and Loutre, 1991; Shakun and Carlson, 2010 ).

What is the YD in the Northern Hemisphere?

The YD is a cold phase which lasted in northern hemisphere from about 12.9 to 11.7 cal. ka BP (ca. 11.0–10.0 14 C ka BP). In Québec, the Saint-Narcisse Moraine ( Figs. 47.1, 47.4, 47.6 and 47.7) was traditionally correlated with this episode ( LaSalle and Elson, 1975; Occhietti, 1980 ), but north of the Saint-Narcisse Moraine, a new outline of ice-front features (Mars-Batiscan Moraine, Figs. 47.1, 47.4, 47.6 and 47.7 ), initially named the Batiscan moraine ( Bolduc, 1995 ), was compared by this author to one of the Salpausselkä moraines of Finland ( Sauramo, 1929; Saarnisto and Saarinen, 2001 ). This ice-front feature was also previously noted in the Charlevoix area, close to the Mars River ( Govare, 1995 ). Robert (2001) has shown that several outlines of glacial features, younger than the Saint-Narcisse Moraine, can be followed as far 100 km west of the Batiscan moraine, at least until the Saint-Maurice River.

When did the ice margin retreat?

In most areas, the ice margin lingered on close to the present coastline until the end of the PBO at 11.4 ka BP when a subsequent phase of abrupt warming occurred ( Björck et al., 1997; Kobashi et al., 2008; Rasmussen et al., 2008). Figure 50.4 shows a selection of dates for the regional onset of ice-margin retreat from the coastal areas based on C14 dates from marine molluscs and lake sediments from coastal lakes (from compilations by Funder and Hansen, 1996; and Bennike and Björck, 2002, supplemented with newer results from Jennings et al., 2006; Sparrenbom et al., 2006b; Hall et al., 2008; Long et al., 2008a; Wagner et al., 2010; Larsen et al., in press ). Radiocarbon dating of this time interval is precarious because of C14 plateaux and, for marine organisms, because of the varying reservoir effects as a consequence of changing ocean circulation ( Björck, 2007; Cao et al., 2007 ). Nonetheless, the lack of a uniform ice-marginal response and the consistently younger ages for warming in lakes and marine environments indicate that the Younger Dryas event and the abrupt warming at its end did not have a profound influence on the ice-sheet margin as a whole, as otherwise expected and modelled ( Weidick et al., 2004; Roberts et al., 2009; Simpson et al., 2009 ). This shows that the response of the ice margin to temperature change is not just a direct function of temperatures, and it underlines the necessity of including field observations in modelling. Also the neighbouring ice sheet on Svalbard lacks distinct traces of Younger Dryas cooling ( Mangerud and Landvik, 2007 ).

Where is the Younger Dryas impact?

In 2018, some researchers interpreted the undated Hiawatha Glacier impact crater in Greenland as evidence for the Younger Dryas impact event due to its location. Two papers were published dealing with an "extraordinary biomass-burning episode" associated with the Younger Dryas Impact.

When were the younger dryas discovered?

The Younger Dryas was first recognized in Denmark in 1901 by Hartz and Mithers, although the term was not created until 1912. However, there were several speculative hypotheses connecting cometary impacts with climatic events dating to about the correct time (circa 10000 BCE) that predate the discovery of the Younger Dryas.

Where are the black mats found?

The evidence given by proponents of a bolide or meteorite impact event includes "black mats", or strata of organic-rich soil that have been identified at over 50 archaeological sites across four continents, primarily in North America and Greenland.

Is there evidence of an extraterrestrial impact at the Younger Dryas boundary?

In 2016, a report on further analysis of Younger Dryas boundary sediments at nine sites found no evidence of an extraterrestrial impact at the Younger Dryas boundary. Also that year, an analysis of nanodiamond evidence failed to uncover lonsdaleite or a spike in nanodiamond concentration at the YDB. Radiocarbon dating, microscopy of paleobotanical samples, and analytical pyrolysis of fluvial sediments " [found] no evidence in Arlington Canyon for an extraterrestrial impact or catastrophic impact-induced fire." Exposed fluvial sequences in Arlington Canyon on Santa Rosa Island "features centrally in the controversial hypothesis of an extra-terrestrial impact at the onset of the Younger Dryas."

How long did the Younger Dryas last?

This means that the event took place about 13,000 years ago and lasted for about 1,300 years. The temperatures dropped massively entering into a near-glacial period where it was cold and windy ...

What were the effects of the Younger Dryas?

Impacts of the Younger Dryas. The Younger Dryas event was not like any normal climate change as therefore was bound to have impacts on the world. It is said that temperature fluctuations not only occurred before and after but also during the phenomenon.

How did the YD period change?

The conditions, however, changed again soon after entering the YD period that ended after 1,300 years when the climate became warm again with Greenland recording a 10°C temperature increase in a decade. This period got its name from Dryas Octopetala which is wildflower whose leaves thrive in the cold and became common during the YD period. Apart from the fact that it is an interesting event in history, the way it ended abruptly is what amazes even more.

What caused the YD?

One of the most common explanations and also widely accepted is that water from Lake Agassiz in North America broke its bank and released freshwater into the Labrador Sea and in turn floated on the salty water. This blocked the Atlantic Meridional Overturning Circulation current which transports heat to the north using its warm waters. This blockade, therefore, led to northern Europe freezing. This is also the Thermohaline Circulation (THC) disruption where the North Atlantic froze while the South Atlantic warmed up. However, this explanation is discredited because research shows a similar water release happened after the end of the YD and led to questions as to why climate was not affected similarly. It is also at the same time supported by research showing that if the Thermohaline Circulation was disrupted then less heat would reach the north from the south.

Why did the water stream change its course and go northward?

A closely related theory related to this is that the water stream changed its course and went northward caused by the melting ice sheet in North America. This, in turn, led to an increased amount of rain in the North Atlantic which sufficed to disrupt the THC.

How long did the Ice Age last?

This happened almost immediately after there was an increase of temperatures after the previous glacial period (14,500 years ago) leading to sudden warming that in turn put an end to the Ice Age period which had lasted for approximately 100,000 years.

Where is the Younger Dryas boundary?

The Younger Dryas boundary lies at the base of the YD black mat. (Comet Research Group / Author Provided)

When Did the Younger Dryas Event Occur?

The Younger Dryas impact is thought to have occurred between 10,800 to 10,900 BC. Again, it might have been caused by the Taurid meteor stream , although this time the general view is that we collided with a swarm of comet debris, rather than a single object. The impact was so devastating and covered such a wide area, that it is thought to be responsible for an entire geological age (a mini ice-age lasting 1,300 years) known as the Younger Dryas period when temperatures in the northern hemisphere were 27 degrees Fahrenheit (15 degrees Celsius) lower than they are today.

How long did the Dryas period last?

The impact was so devastating and covered such a wide area, that it is thought to be responsible for an entire geological age (a mini ice-age lasting 1,300 years) known as the Younger Dryas period when temperatures in the northern hemisphere were 27 degrees Fahrenheit (15 degrees Celsius) lower than they are today.

Why is the Younger Dryas Ice Age happening?

Traditionally, the sudden occurrence of the Younger Dryas ice age is blamed on a switch in massive oceanic circulation currents that transport vast amounts of heat around the globe. In turn, this oceanic switch is blamed on huge flows of cold and salt-free meltwater running off northern ice-sheets. But recent climate simulations suggest that, by themselves, these effects cannot account for the suddenness and magnitude of the Younger Dryas cooling, and a degree of atmospheric dusting is needed.

Was there a crater in Tunguska?

No crater was formed, and due to its remote location, it’s thought nobody was actually killed. Tunguska meteoroid impact, a fraction of the Younger Dryas event. Trees were knocked down and burned over hundreds of square kilometres. (Vizu / Public Domain )

What was the impact of the Younger Dryas?

Firestone et al., 2007, PNAS 104 (41): 16016-16021, proposed that a major cosmic impact, circa 10,835 cal. BCE, triggered the Younger Dryas (YD) climate shift along with changes in human cultures and megafaunal extinctions. Fourteen years after this initial work the overwhelming consensus of research undertaken by many independent groups, reviewed here, suggests their claims of a major cosmic impact at this time should be accepted. Evidence is mainly in the form of geochemical signals at what is known as the YD boundary found across at least four continents, especially North America and Greenland, such as excess platinum, quench-melted materials, and nanodiamonds. Their other claims are not yet confirmed, but the scale of the event, including extensive wildfires, and its very close timing with the onset of dramatic YD cooling suggest they are plausible and should be researched further. Notably, arguments by a small cohort of researchers against their claims of a major impact are, in general, poorly constructed, and under close scrutiny most of their evidence can actually be interpreted as supporting the impact hypothesis.

How did the YDB form?

Based on current data, the following is a preliminary model for formation of the YDB. A comet or asteroid, possibly a previously fragmented object that was once greater than several hundred meters in diameter, entered the atmosphere at a relatively shallow angle (>5° and<30°). Thermal radiation from the air shock reaching Earth’s surface was intense enough to pyrolyze biomass and melt silicate minerals below the flight path of the impactor. Pyrolytic products were oxidized, locally depleting the atmosphere of oxygen, and within microseconds, residual free carbon condensed into diamond-like crystal structures, carbon spherules, carbon onions, and aciniform soot. This involved a carbon vapor deposition like process similar to diamond-formation during TNT detonation. In some cases, carbon onions grew around the nanodiamonds and other nanomaterials. At the same time, iron-rich and silicate materials may have melted to form magnetic spherules. Several seconds later, depending on the height of the thermal radiation source, the air shock arrived. Nanodiamonds, magnetic spherules, carbon spherules, and other markers were lofted by the shock-heated air into the upper atmosphere, where prevailing winds distributed them across the Northern and Southern Hemispheres. We suggest that the above model can account for the observed YDB markers (Israde-Alcántaraa et al, 2012).

What are PDFs in glaciofluvial sediment?

These PDFs are straight, generally penetrative, and spaced down to less than 2 mm. Only a few are decorated by small fluid inclusions, whereas toasting occurs in some grains, i.e., a brown coloration due to intense post-shock hydrothermal alteration of the shock lamellae. The orientations of 37 PDF sets in 10 quartz grains were measured with a five-axis Leitz universal stage. Up to seven different orientations per grain were observed. This distribution is similar to the distribution observed in the central uplifts of large Canadian impact structures, where a threshold shock pressure of >16 GPa was inferred from the presence of PDFs. (Kurt H. Kjær et al Nov 2018)

How deep is the ice bed at the iceberg?

This structure is covered by up to 930 m of ice but has a clear circular surface expression. An elevated rim in the bed topography encloses the relatively flat depression with a diameter of 31.1 ±0.3 km and a rim-to-floor depth of 320 ± 70 m. In the center of the structure, the bed is raised up to 50 m above the surrounding topography, with five radar-identified peaks that form a central uplift up to 8 km wide. The overall structure has a depth-to-diameter ratio of 0.010 ± 0.002 and is slightly asymmetric, with a gentler slope toward the southwest and maximum depth in the southeast of the structure. Two winding subglacial channels, up to ~500 m deep and ~5 km wide, intersect the southeast flank of the circular structure. Before entering the structure, the northern channel merges with the southern channel and then spills over a large breach in the structure’s rim upon entering the main depression. These channels do not have a recognizable topographic expression within the structure. On the downstream side of the structure, there is a second smaller breach in the northwestern portion of the structure’s rim. Ice flows through this second breach to form the tongue-shaped terminus of Hiawatha Glacier. The present ice-sheet margin lies ~1 km past this northwestern rim, and it is the circular depression itself that contains the semicircular ice lobe that extends conspicuously beyond the straighter ice-sheet margin farther southwest. (Kurt H. Kjær et al Nov 2018)

Where do Dryas moraines occur?

Multiple Younger Dryas moraines of alpine glaciers also occur throughout the world, e.g., the European Alps, the Rocky Mts., Alaska, the Cascade Range, the Andes, the New Zealand Alps, and elsewhere.

What caused the Younger Dryas to melt?

The Younger Dryas interruption of the global warming that resulted in the abrupt, wholesale melting of the huge late Pleistocene ice sheets was first discovered in European pollen studies about 75 years ago. Terrestrial plants and pollen indicate that arboreal forests were replaced by tundra vegetation during a cool climate. This cool period was named after the pale yellow flower Dryas octopetella, an arctic wildflower typical of cold, open, Arctic environments. The Younger Dryas return to a cold, glacial climate was first considered to be a regional event restricted to Europe, but later studies have shown that it was a world-wide event. The problem became even more complicated when oxygen isotope data from ice cores in Antarctica and Greenland showed not only the Younger Dryas cooling, but several other shorter cooling/warming events, now known as Dansgaard-Oerscher events.

What were the most abrupt changes in the late Pleistocene?

Among these abrupt changes in climate were: (1) sudden global warming 14,500 years ago (Fig. 1) that sent the immense Pleistocene ice sheets into rapid retreat, (2) several episodes of climatic warming and cooling between ~14,400 and 12,800 years ago, (3) sudden cooling 12,800 years ago at the beginning of the Younger Dryas, and (4) ~11,500 years ago, abrupt climatic warming of up to 10º C in just a few decades. Perhaps the most precise record of late Pleistocene climate changes is found in the ice core stratigraphy of the Greenland Ice Sheet Project (GISP) and the Greenland Ice Core Project (GRIP). The GRIP ice core is especially important because the ages of the ice at various levels in the core has been determined by the counting down of annual layers in the ice, giving a very accurate chronolgoy, and climatic fluctuations have been determined by measurement of oxygen isotope ratios. Isotope data from the GISP2 Greenland ice core suggests that Greenland was more than~10°C colder during the Younger Dryas and that the sudden warming of 10° ±4°C that ended the Younger Dryas occurred in only about 40 to 50. years.

What is the significance of the multiple nature of YD moraines?

The multiple nature of YD moraines in widely separated areas of the world and in both hemispheres indicates that the YD consisted of more than a single climatic event and these occurred virtually simultaneously worldwide. Both ice sheets and alpine glaciers were sensitive to the multiple YD phases.

How did 14C and 10Be change during the YD?

14 C and 10 Be are isotopes produced by collision of incoming radiation with atoms in the upper atmosphere. The change in their production rates means that the Younger Dryas was associated with changes in the amount of radiation entering the Earth’s atmosphere, leading to the intriguing possibility that the YD was caused by solar fluctuations.

Where were the first multiple YD moraines?

Among the first multiple YD moraines to be recognized were the Loch Lomond moraines of the Scotish Highlands. Alpine glaciers and icefields in Britain readvanced or re-formed during the YD and built extensive moraines at the glacier margins. The largest YD icefield at this time was the Scotish Highland glacier complex, but smaller alpine glaciers occurred in the Hebrides and Cairngorms of Scotland, in the English Lake District, and in Ireland. The Loch Lomond moraines consist of multiple moraines. Radiocarbon dates constrain the age of the Loch Lomond moraines between 12.9 and 11.5 calendar years ago.

Did the Dryas occur before or after the YD?

The Younger Dryas was not just a single climatic event. Late Pleistocene climatic warming and cooling not only occurred before and after the YD, but also within it. All three major Pleistocene ice sheets, the Scandinavian, Laurentide, and Cordilleran, experienced double moraine-building episodes, as did a large number of alpine glaciers. Multiple YD moraines of the Scandinavian Ice Sheet have long been documented and a vast literature exists. The Scandinavian Ice Sheet readvanced during the YD and built two extensive end moraines across southern Finland, the central Swedish moraines, and the Ra moraines of southwestern Norway (Fig. 4). 14 C dates indicate they were separated by about 500 years.

Overview

The Younger Dryas impact hypothesis (YDIH) or Clovis comet hypothesis posits that fragments of a large (more than 4 kilometers in diameter), disintegrating asteroid or comet struck North America, South America, Europe, and western Asia around 12,850 years ago, coinciding with the beginning of the Younger Dryas cooling event. Multiple meteor air bursts and/or impacts are claimed to have produced the Younger Dryas (YD) boundary layer (YDB), depositing peak concentrations of platin…

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