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>> JOINING ME NOW IS DR. VICTOR POLYAK, A
RESEARCH SCIENTIST, AS WELL AS DR. YEMANE ASMEROM, A
PROFESSOR AT THE EARTH AND PLANETARY SCIENCES
DEPARTMENT AT UNM. SO, LET ME UNDERSTAND THIS
CORRECTLY. I GUESS THERE'S SOME NEW
EVIDENCE AS TO WHAT, OR WHO KILLED THE WOOLLY MAMMOTH?
>> WE STUDY PALEOCLIMATE USING CAVE FORMATIONS,
MOSTLY STALAGMITES. BY DOING THIS, WE CAN
RECONSTRUCT VERY ACCURATE AND HIGH RESOLUTION RECORDS.
IN THIS RECORD, WE CAN SEE THAT THE TRANSITION
REPRESENTED VERY FAST DRYING OF THE SOUTHWEST.
IT'S ALSO A PERIOD WHEN MEGAFAUNA IN NORTH AMERICA
WENT EXTINCT. WE CAN SEE THAT CLIMATE
STARTED DRYING ABOUT 14 AND A HALF THOUSAND YEARS AGO,
AND THIS DRYING CONTINUED FOR AT LEAST 1500 YEARS.
WE INTERPRET THAT THIS DRYING PERIOD WAS LARGELY
RESPONSIBLE FOR THE EXTINCTION OF THESE LARGE
MAMMALS. >> THAT'S RIGHT HERE IN NEW
MEXICO THIS COULD BE DERIVED.
>> THAT CAME FROM FORT STANTON CAVE IN CENTRAL NEW
MEXICO. FOR THIS TYPE OF RESEARCH,
USING STABLE ISOTOPES, WE PREFER TO HAVE SAMPLES THAT
WERE COLLECTED FAR INTO A CAVE, WHERE THE RELATIVE
HUMIDITY STAYS STABLE AT ABOUT 100% ALL THE TIME.
AND THIS PARTICULAR CAVE IS THE THIRD LONGEST CAVE IN
NEW MEXICO, AND IT'S GROWING.
WE COLLECTED OUR SAMPLES FROM AN AREA THAT'S ABOUT
ONE MILE INTO THE CAVE. >> DR. ASMEROM, DO YOU
CONCUR WITH THIS? >> I THINK TO PUT IT IN
BROAD CONTEXT, THE FASCINATION WITH MEGAFAUNA
ITSELF IS VERY INTERESTING, BUT IT'S ALSO AT THE TIME
THAT HUMANS ESSENTIALLY STARTED TO OCCUPY THE
CONTINENT. SO IT HAS, YOU KNOW, VERY
BROAD IMPLICATIONS FOR THE CLIMATE DYNAMICS AND THE
EVOLUTION OF HUMAN CULTURE, AND THEN ALSO, OF COURSE,
THE FAUNA ITSELF. THIS MEGAFAUNA BASICALLY
BECAME EXTINCT AT ABOUT THE SAME TIME THAT HUMANS WERE
ESSENTIALLY ARRIVING ON THE CONTINENT, AND THE QUESTION
HAS ALWAYS BEEN: DID HUMAN KILLING DO IT, OR WAS IT
CLIMATE? AND THEN RECENTLY, WAS IT
SOME ASTEROID THAT IMPACTED THE EARTH AT THE BEGINNING
OF THE YOUNGER DRIERS? >> SO WHICH IS IT?
OR IS IT A COMBINATION? >> WELL, AGAIN, THE BIG
ISSUE IS THAT WHEN PEOPLE ARE TALKING ABOUT CLIMATE,
THERE WAS NOT REALLY A WELL-DOCUMENTED CLIMATE
HISTORY. SO IT WAS ALL IN THE ABSENCE
OF A VERY WELL-DOCUMENTED CLIMATE HISTORY.
>> NOW WE HAVE IT. >> NOW WE HAVE IT,
PRECISELY, BECAUSE WE HAVE THESE ARCHIVES THAT WE CAN
PRECISELY DATE, YOU KNOW, WITH UNCERTAINTIES, IN THE
RANGE OF LESS THAN A HUNDRED YEARS.
>> THAT'S AMAZING, LESS THAN A HUNDRED YEARS.
>> THAT'S RIGHT. SO WE CAN DATE THAT FOR THE
FIRST TIME, YOU KNOW. WE DON'T HAVE ANY OTHER
ARCHIVE THAT WE CAN DATE THAT WELL IN CONTINENTS FOR
THAT TIME. >> REALLY?
>> YES. SO I THINK WE WOULD LIKE TO
ARGUE THAT, IN FACT, CLIMATE WAS THE MAIN FACTOR FOR THE
DEMISE OF THE MEGAFAUNA. BUT I THINK IMPORTANTLY,
ALSO, IN THAT IS THE CONTEXT IN WHICH THIS WAS OCCURRING.
AS I SAID, HUMANS WERE JUST ARRIVING ON THE CONTINENT.
THEIR LIFESTYLE WAS INITIALLY BASED ON HUNTING
BIG MEGAFAUNA. CLIMATE, IN A SENSE,
DETERIORATED RADICALLY IN A WAY THAT IT HADN'T DONE.
WE HAVE LOOKED AT INDICATIONS FOR THE LAST
50,000 YEARS, AND THERE HADN'T BEEN A DROUGHT THIS
BIG, THIS SUSTAINED RIGHT WHEN THEY'RE GETTING
ESTABLISHED. >> THAT HAD TO BE
CHALLENGING JUST FOR THEM. >> ABSOLUTELY.
IN FACT, AFTER THAT THEY NEVER TRULY RECOVERED THEIR
WAY OF LIFE. THEY WENT INTO THIS
SUBSISTENCE, BASICALLY, OF GATHERER AND HUNTER FOR
ALMOST 10 OR 11,000 YEARS, UNTIL ABOUT 3,000 YEARS AGO
WHEN CLIMATE RECOVERED AGAIN, AGRICULTURE WAS
INTRODUCED. AND SO THIS WAS A VERY,
VERY, VERY DRAMATIC EVENT. IT'S ALMOST KIND OF EERILY
LIKE, I THINK, SOME OF THE ISSUES WE ARE FACING; IN
THIS CASE, OF OUR OWN MAKING.
>> AND THE FACT THAT THIS COULD BE DETERMINED THROUGH
THE STALAGMITES. >> WE USE THESE VERY SHORT
LITTLE ISOTOPES OF URANIUM, THE ELEMENT URANIUM, THROUGH
A SERIES OF THE SHORT LITTLE ISOTOPES TO BECOME WET.
NOW BECAUSE OF THE TECHNOLOGY, WE HAVE THIS NEW
MACHINE, FOR EXAMPLE, THAT ALLOW US TO BASICALLY
MEASURE A FEW MILLIGRAMS OF THIS STUFF.
YOU SEPARATE THE ELEMENT OF INTEREST; IN THIS CASE, THE
ELEMENT URANIUM AND THE ELEMENT THORIUM.
AND THEN YOU PUT IT INTO THE MULTICOLLECTOR-INDUCTIVELY
COUPLED PLASMA MASS SPECTROMETER.
IT IONIZES THE SAMPLES. YOU HAVE A TEMPERATURE OF
8000 KELVIN, WHICH IS HOTTER IN SOME WAYS THAN THE
SURFACE TEMPERATURE OF THE SUN, AND THEN IT GIVES YOU
THESE IONS. YOU GET A VERY WELL RESOLVED
ISOTOPE FIX OF EACH ELEMENT OF INTEREST.
>> ONE OF THE CHALLENGES, BY INVOKING PALEOCLIMATE AS
THE CAUSE OF EXTINCTION, HAS BEEN: WHY DIDN'T THIS
HAPPEN IN THE PREVIOUS INTERGLACIAL PERIOD, OR THE
INTERGLACIAL PERIOD BEFORE THAT?
ABOUT EVERY HUNDRED THOUSAND YEARS, WE HAVE A GLACIAL
PERIOD, AND THEN WE HAVE A GLACIAL/INTERGLACIAL
TRANSITION, LIKE WE'VE SEEN FOURTEEN AND A HALF THOUSAND
YEARS AGO. SO INVOKING PALEOCLIMATE HAS
ALWAYS RUN UP AGAINST THAT PROBLEM: WHY DIDN'T THEY GO
EXTINCT DURING THIS PREVIOUS GLACIAL AND INTERGLACIAL.
WE THINK THAT THIS LAST GLACIAL PERIOD WAS MORE
INTENSE THAN PREVIOUS GLACIALS, AND THAT ON TOP
OF, YOU KNOW, A VERY RAPID GLACIAL/INTERGLACIAL
TRANSITION MAY HAVE BEEN TOO MUCH FOR A LOT OF THE LARGER
FAUNA TO RESPOND TO. >> AND PART OF THE SORT OF
CLIMATE DISCUSSION IN THE PAST, FOR EXAMPLE, IS PEOPLE
COULDN'T JUST QUITE FIGURE OUT, WAS IT TOO COLD?
SO SOME OF THE LITERATURE WAS SAYING, IT WAS THE COLD
WEATHER THAT KILLED THEM. AND THERE WERE OTHERS THAT
SUGGESTED THE DROUGHT. IN FACT, I THINK IT'S THE
DOUBLE PUNCH, BASICALLY. IN A SENSE, YOU HAVE A VERY
SEVERE GLACIAL THAT'S RESTRICTED THE RANGE IN A
PARTICULAR AREA, AND THEN AT ABOUT 14,500 YEARS AGO,
BASICALLY, YOU HAVE THE MOST SEVERE DROUGHT.
IT'S JUST AMAZING. I MEAN, WE SEE THESE THINGS
JUST RAPIDLY RISING, AND THEN SUSTAINED FOR ANOTHER
1500 YEARS. >> AND YOU ACTUALLY HAVE A
SAMPLE OF THIS STALAGMITE? >> YES, THIS IS A SAMPLE
FROM FORT STANTON CAVE. AND IT'S A STALAGMITE THAT'S
BEEN SLICED DOWN THE CENTER. HERE IS WHAT THE EXTERIOR
LOOKS LIKE. IT'S BEEN CUT IN HALF, SO
THAT WE CAN SEE ALL THE GROWTH LAYERS.
>> LIKE A TREE, THE RINGS. >> LIKE A TREE, AND IT
GROWS UPRIGHT LIKE THIS, AND A WATER DROPLET COMES FROM
ABOVE, HITS THE TOP OF IT AND DEPOSITS A TINY BIT OF
CALCIUM CARBONATE. THIS LAYER OF CALCITE WAS
PRECIPITATED ABOUT 160,000 YEARS AGO.
AND THEN AS YOU GO UP, YOU KNOW, YOU GO UP 159,000,
158,000, UP TO 130,000 YEARS AGO WHERE THIS PARTICULAR
GLACIAL ENDED AND THE CLIMATE DRIED, AND THAT'S
REPRESENTED BY THIS GROWTH HIATUS.
THE IMPACT THEORY OF EXTINCTION OF THESE
MEGAFAUNA CALL FOR THE EXTINCTION TO HAPPEN RIGHT
AT THE BEGINNING OF THE YOUNGER DRIEST PERIOD,
13,000 YEARS AGO. OUR CARBON AND URANIUM
ISOTOPE RECORDS DO NOT SEE THIS IMPACT.
WE DON'T SEE DRASTIC CLIMATE CHANGE AT THAT TIME.
WE JUST SEE A CONTINUAL RISING OF CARBON THROUGH IT
AND UP INTO THE HALOCLINE. >> HOW DOES IT IMPACT WHAT
WE'RE EXPERIENCING TODAY CLIMATE-WISE?
>> THE FACT THAT WE HAVE A VERY COMFORTABLE SORT OF AIR
CONDITIONED, SO TO SPEAK, PLANET IS BECAUSE WE HAVE
GREENHOUSE GASES. NOW IF, IN FACT, THE
GREENHOUSE GASES LEAD TO THIS WARMING, WHICH WE LIKE,
ADDING MORE GREENHOUSE GASES WILL ALSO INCREASE THE
WARMING. THAT'S JUST SIMPLY
ELEMENTARY; RIGHT? WHAT WE DON'T UNDERSTAND,
AND I THINK THIS IS THE LEGITIMATE POINT, IS THAT TO
THE EXTENT THAT CLIMATE IS VERY PROVINCIAL, YOU HAVE TO
BE ABLE TO START TO UNDERSTAND HOW THIS GLOBAL,
AND CLIMATE CHANGE IN GENERAL, IS GOING TO IMPACT
DIFFERENT REGIONS, OBVIOUSLY, WHETHER IT'S OUR
PREDECESSORS, THE ANCESTORIAL AMERICANS, AND
THEN SUBSEQUENTLY ALL THE WAY TO THE MODERN.
IN FACT, IT'S INTIMATELY, INTIMATELY RELATED TO
CHANGES OF CLIMATE. THE KIND OF CLIMATE CHANGE
WE'VE LOOKED AT, FOR EXAMPLE, DURING THIS PERIOD
IS DRAMATIC. WE HAVEN'T SEEN ANYTHING
LIKE THAT. BUT EVEN LESS DRAMATIC
CLIMATE CHANGE, FOR EXAMPLE, DURING THE MEDIEVAL WARM
PERIOD AND THE ICE AGE CREATED HAVOC IN THIS
REGION. SO I THINK, IN A BROAD
SENSE, WHAT WE'RE DOING IS PART OF THIS GREAT EFFORT
TO, IN A SENSE, LOOK AT CLIMATE DYNAMICS.
>> WHAT KILLED THE WOOLLY MAMMOTH?
>> WE THINK ONE OF THEM WAS IMPORTANTLY, NOT THE MOST
IMPORTANT FACTORS, WAS THE DOUBLE PUNCH OF CLIMATE FROM
A VERY WET REGIONALLY RESTRICTED SETTING AS A
RESULT OF THE GLACIAL PERIOD, AND THEN IMMEDIATELY
FACED WITH THIS EXTRAORDINARY DROUGHT,
UNPRECEDENTED FOR THE LAST 50,000 YEARS THAT WE HAVE
LOOKED AT IN DETAIL, SUSTAINED OVER LONG PERIODS
OF TIME. IN TERMS OF LOOKING AT
TIMING OF EXTINCTION AND TIMING OF CLIMATE CHANGE,
THE COINCIDENCE IS JUST TOO IMPORTANT, OR TOO --
>> YOU CAN'T IGNORE IT. >> YOU CAN'T IGNORE IT.
>> THANK YOU BOTH. I THINK IT'S A FASCINATING
SUBJECT TO DELVE INTO, AND CERTAINLY ONE THAT HAS GREAT
RELEVANCE TO LIVING IN NEW MEXICO.
>> ABSOLUTELY. >> THANK YOU.