0.0
In three years, the temperature in Greenland fell
2.68
by 10 degrees Celsius.
4.8
Not over a decade.
6.16
Not over a century.
7.82
Three years.
9.359
Three years.
11.019
This happened approximately 12,900 years ago.
15.4
The evidence is preserved in the layered ice
18.339
of the Greenland Ice Sheet in the GISP
21.46
-2 and GRIP course extracted by international research
24.96
teams in the 1990s.
26.82
The cooling was global.
28.76
North America dropped three degrees.
31.28
Europe
32.0
dropped between two and six.
34.0
The planet's climate did not slowly degrade.
37.039
It collapsed.
40.12
The event is called the Younger Dryas.
43.1
It lasted approximately 1,300 years.
47.159
During that
48.159
interval, the Woolly Mammoth, the American Mastodon, the
52.039
Sabertooth Tiger, the Giant
54.1
Grounslaw, and the Giant Mastodon were all destroyed.
54.96
And most of the rest of the Pleistocene
57.259
megafauna of North America disappeared.
59.84
The Clovis people, the dominant human culture of
63.28
the continent,
64.0
vanished from the archaeological record at the same
66.739
boundary.
67.9
For over 50 years, geologists, paleoclimatologists,
73.06
and archaeologists have tried to determine what caused
76.859
it.
77.26
In 2007, a research consortium proposed an answer
81.4
that would, if true, change the entire chronology
84.5
of the late Pleistocene.
86.04
The answer was a cosmic impact.
89.76
What followed was 18 years of evidence,
92.92
counter-evidence, vindication, retraction, and a single Greenland
97.7
crater that briefly looked like
99.719
the smoking gun and then turned out to
102.0
be 58 million years old.
104.64
This is Fragment Zero, Case File 44,
108.26
the planet's most consequential climate event in the
111.34
last 20,000 years and the open question
113.959
that
114.319
geology has not been able to close.
116.42
How would you understand what was lost?
118.68
You have to understand what an ice core
120.9
is.
121.9
When snow falls on Greenland, it does not
124.859
melt.
125.359
It accumulates.
126.819
Each year's snow is buried by the next
129.439
year's snow, and over centuries the lower
131.84
layers compress into ice.
133.759
Air bubbles trapped between snowflakes preserve a sample
137.759
of the
138.039
atmosphere from the year the snow fell.
140.219
Chemical impurities— dust, sulfate from distant volcanism,
144.319
volcanoes, sea salt from coastal storms, soot from
147.58
continental fires, isotopes of oxygen
150.3
that record temperature, are locked into the ice
153.319
in chronological order, layer by layer,
156.039
year by year.
157.74
A Greenland ice core is a vertical timeline.
160.759
The top is recent, the bottom is older
163.74
than human civilization.
165.34
The Greenland Ice Sheet Project.
167.28
Two core, drilled at a remote station called
170.9
Summit between 1989 and 1993, extends 3,053
176.259
meters into the ice.
177.62
The deepest layers it sampled formed over 100
180.479
,000 years ago.
182.02
When researchers in Boulder, Copenhagen, and Bern read
185.36
the GISP-2 record, they found that
188.039
at a depth corresponding to approximately 12,834
191.78
years before the present, something
193.96
extraordinary happened.
195.5
The oxygen isotope record.
197.259
The ratio that records mean annual temperature dropped
200.0
sharply.
200.759
The transition was not smooth.
202.939
It happened, in geological terms, instantaneously.
206.62
A subsequent reanalysis, using high-resolution layer counting,
210.599
determined that the cooling
211.939
at Greenland was complete within three to four
214.699
years.
215.58
For comparison, the climate change caused by the
219.099
1815 eruption of Mount Tambora, the
221.759
largest volcanic event in recorded history, which produced
225.06
the so-called year without
226.62
a summer of 1816, cooled the global average
229.78
temperature by about half a degree Celsius
232.159
for one year.
234.17
The Younger Dryas Onset cooled Greenland by 10
237.439
degrees and held it there for over a
239.62
millennium.
240.77
Whatever happened at 12,900 years before present
244.219
was an order of magnitude larger than anything
247.18
geology has documented within the human historical record.
252.86
The ecological consequences are cataloged in the bone
256.319
record.
256.6
At sites across North America, Clovis kill sites
260.779
in Arizona, Murray Springs, Lake Theo,
263.86
the La Brea Tar Pits in California, the
266.319
bones of the Great Pleistocene fauna stop appearing
269.139
in the sediment column at the Younger Dryas
271.48
boundary.
272.1
The species that vanished include Mammuthus columbi, the
275.42
Colombian mammoth, ranging across
277.1
the southern United States, Mammuthus primigenius, the woolly
280.959
mammoth, across Alaska and the
282.819
Yukon, Mammut americanum, the American mastodon.
286.24
Small-sized mammoth, large-sized mammoth, large-sized
286.579
mammoth, large-sized mammoth,
286.579
Mammuthus cam belli, Ab viable, long-lished abalone,
286.68
long- presenting, Mammuthus Shmeledon
287.06
fatalis, the saber-toothed cat, Megalonix the giant
290.379
ground sloth, Camelops the Western
292.519
camel, Equus the New World horse, Glyptotherium the
296.079
armored armadillo relative, the size of
298.3
a small car, 35 genera of large North
302.079
American mammals went extinct in a window so
305.459
narrow
305.98
that paleontologists initially had difficulty resolving it at
310.36
all.
310.86
The bones are present in the layers below
313.439
the Younger Dryas boundary and absent above
316.12
it.
316.579
The transition is, in many sections, less than
319.74
10 centimeters of sediment.
322.08
Above the bones, in many of these sites,
324.699
geologists noted a thin, dark layer of charcoal
327.72
-rich sediment that they began calling the black
330.68
mat.
331.18
The black mat appears across roughly 10 million
334.339
square kilometers of the North American continent.
337.62
Its composition includes high concentrations of carbon, soot,
341.62
and ash.
342.68
It is the signature of an enormous burning
345.12
event.
345.439
Continent-scale wildfires, occurring at the precise stratigraphic
350.279
moment that the megafauna disappeared and the climate
353.459
collapsed.
355.779
In 2007, a group of researchers led by
359.24
Richard Firestone, a nuclear chemist at Lawrence Berkeley
362.439
National Laboratory,
363.86
published a paper in the Proceedings of the
366.16
National Academy of Sciences titled,
368.439
Evidence for an Extraterrestrial Impact, 12,900 Years
372.98
Ago That Contributed to the Megafaunal Extinction.
375.439
The paper proposed a specific mechanism.
381.259
A comet, or asteroid, had broken apart in
384.579
the atmosphere above the Laurentide Ice Sheet.
387.22
The kilometers-thick ice covering most of Canada
390.5
and the northern United States at the end
393.199
of the Pleistocene.
394.54
The impact had not produced a single large
397.519
crater.
398.24
It had produced a swarm of airbursts and
401.379
surface fragments distributed across the continent.
404.72
The impact had not produced a single large
405.42
crater.
405.439
Resulting energy ignited continental-scale fires, producing the
409.399
black mat.
410.18
The heat and dust loaded into the upper
413.18
atmosphere blocked solar radiation, triggering the rapid
417.18
Younger Dryas cooling.
419.06
The shock waves and fires, the evidence Firestone
422.12
and his co-authors marshaled, was substantial.
424.74
At the precise Younger Dryas boundary layer in
427.899
25 sites across North America and Europe,
430.579
they identified concentrations of materials associated with cosmic
434.92
impacts, microscopic
436.339
spherules of melted glass formed when impact heat
439.86
vaporizes silicate rock, magnetic microspherules,
444.74
carbonspherules, nanodiamonds, vanishingly small diamond crystals that form
450.18
only under
451.019
the extreme pressure and temperature conditions of an
453.779
extraterrestrial impact, iridium, the
457.36
element that defines the Cretaceous-Paleogene boundary.
460.199
The argument had a name, the Younger Dryas
465.779
Impact Hypothesis.
467.22
The research consortium that continued to publish in
470.259
support of it called themselves
471.92
the Comet Research Group.
473.819
Over the next decade, they would publish dozens
476.48
of papers documenting the boundary layer markers
479.04
at sites in North America, Europe, the Middle
481.839
East, South America, and Antarctica.
484.839
If the hypothesis was correct, it represented the
488.5
most consequential cause of the Cretaceous-Paleogene
490.18
event in the history of human civilization, coinciding
493.899
with the disappearance of the
495.18
dominant human culture of the Americas and the
497.939
most rapid climate event in the geological
500.42
record.
502.6
Then, in 2018, a separate research team discovered
506.92
something that initially appeared to settle
509.339
the question entirely.
510.98
A Danish-led consortium analyzing high-resolution radar
515.22
data of the Greenland Ice Sheet identified
518.039
a perfectly circular bedrock depression beneath the Hiawatha
522.299
Glacier in northwestern Greenland.
524.34
The depression was 31 kilometers across.
527.84
It had the morphology, the central peak, the
531.22
elevated rim, the disturbed bedrock of an
534.399
impact crater.
535.84
The team flew aerial surveys.
538.2
They drilled meltwater samples from rivers flowing out
541.48
from under the ice.
542.679
The meltwater contained shocked quartz grains, partially melted
546.679
granite fragments, and elevated
548.539
platinum concentrations.
550.24
The crater was real.
551.84
The initial dating estimate, based on the youth
555.539
of the overlying ice and the freshness
557.72
of the bedrock deformation, suggested the impact had
560.94
occurred within the past 100,000 years.
564.519
12,900 years before present is within 100
568.82
,000 years.
570.299
The Hiawatha crater became, briefly, the most discussed
574.34
feature in impact geology.
576.24
If it had formed at the Younger Dryas
578.44
boundary, it was the smoking gun the comet
580.98
research
581.299
group had spent 11 years arguing for.
584.08
A 31-kilometer crater is consistent with an
587.08
impactor of approximately 1 kilometer in diameter,
590.08
a body large enough to ignite continental fires,
593.039
eject enough debris to perturb the
595.179
atmosphere, and trigger climate collapse at exactly the
598.12
magnitude observed.
599.559
For four years, scientists waited for a precise
603.019
date on the Hiawatha impact.
607.0
In March of 2022, the geological survey of
611.279
the Hiawatha crater revealed that the crater
611.279
was a natural history museum.
611.659
The National Geological Survey of Denmark and Greenland,
613.44
in collaboration with the Natural
615.259
History Museum of Denmark and Sweden's Geological Survey,
619.139
published the result of two independent
621.519
dating analyses.
623.3
The first was argon, argon dating of sand
626.679
grains from sediment downstream of the crater.
629.419
The second was uranium-lead dating of zircon
632.98
crystals from impact melt rock recovered from
635.919
the meltwater.
636.679
Both methods returned the same answer to within
640.019
statistical uncertainty.
641.259
The Hiawatha crater formed 57.99 million years
646.559
ago, plus or minus 0.54 million.
650.72
Late Paleocene During an interval when Greenland was
654.519
covered
654.899
in temperate forest, when there was no ice
657.159
sheet, when the early ancestors of modern
659.519
primates were just beginning to diversify, approximately 57
663.639
,977,000 years before any
667.779
human being existed.
669.879
Brandon Johnson
671.259
An impact modeler at Purdue University and a
673.759
co-author of the dating paper, told the
676.059
journal Science that the result, quote, probably means
679.84
it is safe to put the Younger Dryas
681.899
impact hypothesis back to rest for a while.
684.799
The crater is real.
686.46
It is one of the 25 largest known
689.059
impact structures on the planet.
691.1
It is just 60,000 times too old
693.779
to be relevant to the question it had
695.519
appeared to answer.
698.22
The Hiawatha date eliminated the most physically significant
701.24
impact data in the history of
701.259
the Hiawatha crater.
701.539
The Hiawatha crater is one of the most
701.539
highly compelling pieces of evidence for the impact
703.379
hypothesis.
704.46
The next three years would test whether the
707.0
rest of the case could survive.
708.96
In 2025, the journal Scientific Reports, a peer
714.159
-reviewed, open-access journal published
716.419
by the Nature Group, retracted a 2021 paper
719.94
authored by members of the Comet Research Group.
722.96
The paper had claimed that the Bronze Age
725.58
city of Tell el-Hammam, located near the
728.46
Dead Sea,
729.159
had been destroyed by a cosmic airship.
731.259
Waters interspersed with water within the Standing Valley
737.74
of Ibulaa and after three
740.519
Premiere of Streia del Gano waterfall hollowed by
741.5
sparks contain is indeed a strong wind.
741.6
goin It was the second retraction of a
745.179
Comet Research Group paper from Scientific Reports
747.84
in three years.
749.039
The first, in 2023, had concerned a separate
753.019
set of putative impact markers from a different
755.74
site.
756.419
Independent statisticians who had requested the raw data
759.879
for reanalysis refused to re-arrange
761.259
reported that key figures in the retracted papers
763.759
showed evidence of selective sample inclusion
766.539
and post-hoc curve fitting, patterns inconsistent with
770.399
the conclusions the authors had drawn from
772.419
them.
772.94
The retractions did not, by themselves, falsify the
776.96
Younger-Dryas impact hypothesis.
779.0
They concerned auxiliary applications of the hypothesis to
782.779
other proposed impact events.
784.659
But within the geological community, they had a
787.74
chilling effect on the broader research program.
789.899
Reviewers became more skeptical.
792.36
Funding agencies became more cautious.
794.72
Independent attempts to
796.1
replicate the original Firestone findings became more critical.
799.539
By the middle of 2025,
802.08
the Comet Research Group's continued defenders included an
805.7
active core of perhaps 30 researchers
808.08
across multiple institutions, publishing primarily in lower-impact
812.539
journals.
813.179
The broader paleoclimate
814.84
community had largely shifted to the alternative hypothesis
817.6
that the Younger-Dryas was trying to
819.879
trigger by a freshwater pulse from the collapse
822.019
of glacial lake Agassiz into the North Atlantic,
824.919
shutting down the thermal haline circulation that warms
827.879
the North Atlantic,
828.799
shutting down the thermal haline circulation.
831.519
The freshwater shutdown hypothesis explains the
835.279
cooling.
835.779
It does not, on its own, explain the
838.86
megafaunal extinction, the continental burn layer,
842.279
the platinum anomaly in the Greenland ice, or
845.259
the carbon and nanodiamond sphere rules at 25
848.48
sites
849.2
across the world.
849.86
The Younger-Dryas hypothesis did not, by themselves,
849.86
falsify the Younger-Dryas hypothesis.
849.879
The platinum spike is the part that has
854.799
not gone away.
855.98
In 2013, a team led by Mikhail Pataev
859.639
at Harvard
860.2
published a paper in PNAS titled Large PT
863.86
Anomaly in the Greenland Ice Core Points to
866.539
a Cataclysm at
867.5
the Onset of Younger-Dryas.
869.519
Their high-resolution analysis of the GISP-2
872.86
ice core at the Younger-Dryas
874.519
boundary showed that the platinum concentration in the
877.34
ice increased by a factor of approximately
879.82
100 for a period spanning roughly 21 years.
883.559
The platinum is real.
885.399
The ice is undisturbed.
887.44
The chronology is precise.
889.46
Platinum is not concentrated in continental crustal rocks.
893.62
It is concentrated in iron meteorites and in
897.019
the cores of differentiated bodies.
899.2
A 100-fold increase in atmospheric platinum deposition
903.5
over approximately two decades
905.36
is consistent with sustained input of extraterrestrial material.
909.82
Either from a single large impact distributing fragments
913.12
across the Earth or from a sustained
915.419
shower of smaller bodies, the duration is too
918.679
long to be a single instantaneous event and
921.379
too
921.539
short to be a slow natural background variation.
924.58
No alternative geological mechanism for the platinum
928.08
spike has been published.
929.58
The black mat is also real.
932.1
Its distribution across 10 million square
935.08
kilometers of North American sediment, its timing precisely
938.779
coincident,
939.82
with the Younger-Dryas boundary, and its high
942.46
concentrations of soot, charcoal, and high-temperature
945.86
combustion products are accepted by both proponents and
949.039
critics of the impact hypothesis.
951.639
The disagreement is not about whether the black
954.059
mat exists or what it indicates—massive
957.22
continental burning—but about what caused the burning.
961.12
In 2024, a team that included James Kennett,
965.019
the original co-author on the 2007 Firestone
968.059
paper, published a paper in the New York
969.799
Times.
969.82
In 2038 the paper was published in aaporvius
973.299
hundred times the name for the paper, but
975.399
the paper was not considered valid until 2004.
976.5
The paper is still currently under the spa
987.34
formal city review.
988.159
After 6 years of operating,將иц0the%, years later,
989.179
the data is still public.اط҉Geo҉҉҉no҉
997.72
ĉo҉ăo҉nt҉o҉ht҉,ulo҉m҉n҉o҉҉n҉o҉ali,
999.24
as of early 2026, is this.
1002.539
Something extreme happened 12,900 years ago.
1006.779
The data are
1007.879
unambiguous on this point.
1009.679
Greenland's annual temperature fell by 10 degrees in
1012.779
less than a
1013.379
decade.
1014.039
North American megafauna underwent extinction at a rate
1017.179
not seen in any subsequent
1018.679
period of geological history.
1020.779
A continental burn layer was deposited from California
1023.7
to New York.
1024.619
The atmosphere over the northern hemisphere received approximately
1027.88
100 times its usual
1029.88
platinum loading, deposited over a period of roughly
1032.72
20 Earth years.
1034.14
A small but real
1035.38
population of impact, diagnostic markers, shocked quartz, microspherules,
1040.319
nanodiamonds,
1041.279
magnetic spherules, appear in the boundary sediment at
1044.119
multiple sunsets.
1044.839
The hypothesis
1045.96
that this combination of evidence was caused by
1048.859
a cosmic impact has produced 35 published
1051.92
peer-reviewed papers in support.
1053.9
More
1054.38
In the
1054.599
In critique, two retractions, one apparently perfectly placed
1058.64
crater that turned out to be
1060.22
60,000 times too old, and an active
1062.98
scientific debate that has now spanned 18 years
1066.0
without
1066.359
resolution.
1067.579
The hypothesis that the event was caused entirely
1070.9
by the collapse of a glacial
1072.539
lake into the North Atlantic does not, by
1075.579
itself, account for the platinum, the burn layer,
1078.619
the impact markers, or the extinction pattern.
1081.48
It accounts for the cooling.
1083.259
It is the
1084.14
consensus answer for the cooling.
1085.9
It is an incomplete answer for everything else.
1089.299
This is what the data permit us to
1091.619
say.
1092.019
A planetary-scale event occurred.
1094.819
Its mechanism
1095.799
remains formally undetermined.
1098.14
The evidence is preserved in ice cores that
1100.859
have been read,
1101.64
in sediment layers that have been mapped, and
1103.94
in the silence of the bone record across
1106.0
an entire
1106.74
continent.
1108.059
The interpretation has been disputed across multiple generations
1111.44
of researchers.
1112.799
The dispute has
1113.9
not been settled by the discovery of any
1115.9
one piece of evidence.
1117.279
It has been narrowed by the
1118.9
elimination of specific candidates.
1121.38
Hiawatha is too old.
1123.2
Tell el-Hammam was misinterpreted.
1125.44
Certain markers have not survived independent replication.
1129.259
What remains is the platinum,
1131.44
the burn layer, the extinctions, the climate collapse,
1134.4
and the absence of a single agreed
1136.38
mechanism.
1138.9
There is a reason this case continues to
1141.599
be worth tracking.
1142.44
The Younger Dryas was not the most distant
1145.619
event in Earth's climate record.
1147.22
It is among the most recent.
1149.18
It happened during the lifetimes of the immediate
1151.68
ancestors of every
1153.019
living human being.
1154.299
It occurred at the start of the geological
1156.66
period, the Holocene, in which all
1159.18
of recorded human history takes place.
1161.299
The atmospheric and oceanic systems that produced
1164.279
the rapid cooling are the same atmospheric and
1167.119
oceanic systems that govern climate today.
1169.599
Whatever mechanism initiated a ten-degree
1172.2
temperature drop in three years has not been
1174.519
excluded from the present.
1175.92
If the event was
1177.259
caused by an impact, then the relevant question
1179.88
is the frequency of such impacts.
1182.4
Modern surveys
1183.46
of near-Earth objects estimate that bodies capable
1186.279
of producing continent-scale damage
1188.44
strike the Earth on a timescale of approximately
1191.039
100,000 years.
1192.98
Within that statistical window,
1195.16
12,900 years is recent.
1197.66
Another such event is not predictable.
1200.119
It is not impossible.
1202.2
The event is the same even if it
1202.579
is a momentous event.
1202.579
But what happens if the event is caused
1203.339
entirely by a freshwater pulse from a collapsing
1206.7
glacial lake?
1207.68
The consensus mechanism.
1209.319
Then the precondition was the existence of an
1212.099
unstable continental ice sheet that could release
1214.819
several hundred thousand cubic kilometers of freshwater into
1218.2
the North Atlantic in a short
1219.619
interval.
1220.299
The Laurentide ice sheet that collapsed at the
1223.319
end of the Pleistocene no longer exists.
1225.98
The Greenland ice sheet, which does exist, contains
1229.259
roughly 24,000 cubic kilometers of ice,
1232.2
of ice.
1232.7
It is currently losing mass at an accelerating
1235.42
rate.
1236.16
These are not equivalent
1237.799
risks.
1238.64
They are different categories of risk.
1241.42
They produce, however, similar outputs at sufficient
1244.819
magnitude, rapid disruption of the thermal hailing circulation,
1249.0
regional cooling of multiple degrees
1251.079
within years to decades, extinction-grade ecological pressure
1255.599
on species that cannot
1257.259
adapt at that pace.
1259.16
The black mat is preserved in the sediment.
1262.18
The platinum is preserved in the
1264.38
ice.
1264.96
The megafauna are gone.
1268.5
The Comet Research Group continues to publish.
1271.839
The retractions did
1273.359
not silence them.
1274.38
The Hiawatha date did not falsify their hypothesis.
1277.94
They are arguing for
1279.42
the proposition that a specific kind of cosmic
1282.22
event happened during the time of human witnesses,
1285.119
that some component of human
1287.079
cultural memory may preserve fragmentary records of that
1290.44
event, and that the geological signature
1292.539
of such an event has been misclassified for
1295.18
over 50 years because the relevant markers were
1298.16
not
1298.339
recognized as impact-related.
1300.5
The mainstream paleoclimate community has not accepted this
1304.7
argument.
1305.359
The mainstream paleoclimate community has also not, to
1309.579
date, produced a complete
1311.16
alternative explanation that accounts for every component of
1315.18
the boundary layer evidence.
1317.079
What we know is this.
1318.94
There is a layer of sediment under our
1321.299
feet, in the southwestern
1322.92
United States, in the Carolinas, in Belgium, in
1325.88
Syria, in Patagonia, in South Africa, that
1328.92
is darker than the layers above and below.
1331.72
The layer is 12,900 years old.
1335.16
It contains
1335.88
the burned signature of forests that no longer
1338.559
exist, the bone fragments of animals whose
1341.5
lineages ended at that layer, traces of metals
1344.359
that do not concentrate in terrestrial rocks,
1346.619
and crystals deformed by pressures that do not
1349.619
naturally occur in surface geology.
1351.88
A planet does
1353.119
not record this kind of layer often.
1355.4
When it does, the explanation eventually comes.
1358.94
The Cretaceous-Paleogene boundary, which killed the non
1362.559
-avian dinosaurs 66 million years ago,
1365.44
was correctly attributed to an asteroid impact only
1368.579
in 1980, more than a hundred years after
1371.66
the boundary was first recognized.
1373.599
The Permian-Triassic extinction,
1375.96
the largest extinction in the history of human
1376.599
history, was the largest extinction in the history
1376.599
of human history, the largest in Earth's history,
1377.819
was not satisfactorily attributed
1379.539
to volcanic activity until the late 1990s, more
1383.24
than a century after the geological boundary
1385.48
was identified.
1386.66
The Younger Dryas boundary was identified in 1935.
1391.099
The Firestone hypothesis
1393.1
is 18 years old.
1394.72
The Hiawatha dating is four years old.
1397.64
The Tell el-Hammam retraction is
1399.96
one year old.
1400.9
The platinum spike has been measured but not
1403.48
explained.
1404.38
These cases close
1405.9
on geological timescales, not human ones.
1409.119
This is Fragment Zero, Case File 44.
1412.779
The Younger
1413.7
Dryas.
1414.64
Subscribe.
1415.779
Turn on notifications.
1417.72
Because the layer is real, the mechanism is
1420.9
not yet
1421.339
known, and the next time someone tells you
1424.099
a planetary catastrophe must announce itself
1426.599
in advance, you will know how long it
1429.0
takes for the announcement to be understood.
1431.259
We
1431.92
will be watching.
1433.099
We will be listening.
1434.539
The Ice has been waiting 12,900 years
1438.44
to be read.
