The document discusses two main theories for what caused the extinction of the dinosaurs: 1) The Alvarez hypothesis proposes that a massive meteorite impact 66 million years ago filled the atmosphere with debris and drastically altered the climate. Evidence for this includes an iridium layer and the Chicxulub impact crater in Mexico. 2) However, some scientists argue volcanic activity from the Deccan Traps in India, which erupted between 60-65 million years ago, could have emitted gases that changed the climate. Supporters note climate changes predated the impact and point to volcanism as a more frequent potential cause of extinction.

1. Why did the dinosaurs go extinct?
One of the most well-known theories for the death of the dinosaurs is the Alvarez hypothesis,
named after the father-and-son duo Luis and Walter Alvarez. In 1980, these two scientists
proposedthe notionthat a meteorthe size of a mountainslammedintoEarth 66 millionyears
ago, filling the atmosphere with gas, dust, and debris that drastically altered the climate.
Theirkeypiece of evidence isanoddlyhighamountof the metal iridiuminwhat’sknownasthe
Cretaceous-Paleogene,orK-Pg,layer—thegeologicboundary zonethatseemstocapanyknown
rock layers containing dinosaur fossils. Iridium is relatively rare in Earth's crust but is more
abundantin stonymeteorites,whichledthe Alvarezstoconclude thatthe mass extinctionwas
causedby an extraterrestrial object.The theorygainedevenmore steamwhenscientistswere
able to link the extinction event to a huge impact crater along the coast of Mexico’s Yucatán
Peninsula. At about 93 miles wide, the Chicxulub crater seems to be the right size and age to
account for the dino die-off.
In2016, scientistsdrilledarockcore insidetheunderwaterpartof Chicxulub,pullingupasample
stretching deep beneath the seabed. This rare peek inside the guts of the crater showed that
the impact would have been powerful enough to send deadly amounts of vaporized rock and
gases into the atmosphere, and that the effects would have persisted for years. And in 2019,
paleontologistsdigginginNorthDakotafounda treasure trove of fossilsextremelyclose tothe
K-Pg boundary, essentially capturing the remains of an entire ecosystem that existed shortly
before the mass extinction. Tellingly, the fossil-bearing layers contain loads of tiny glass bits
called tektites—likely blobs of melted rock kicked up by the impact that solidified in the
atmosphere and then rained down over Earth.
Volcanic fury
However, other scientists maintain that the evidence for a massive meteor impact event is
inconclusive, and that the more likely culprit may be Earth itself.
Ancient lava flows in India known as the Deccan Traps also seem to match nicely in time with
the endof the Cretaceous,withmassive outpouringsof lavaspewingforthbetween 60 and 65
millionyearsago.Today,the resultingvolcanicrockcoversnearly200,000 square milesinlayers
that are inplacesmore than6,000 feetthick.Suchavast eruptive eventwouldhave chokedthe
skieswithcarbondioxide andothergasesthatwouldhavedramaticallychangedEarth’sclimate.
Proponentsof thistheorypointto multiplecluesthatsuggestvolcanismisabetterfit.For one,
some studies show that Earth’s temperature was changing even before the proposed impact
event. Other research has found evidence for mass die-offs much earlier than 66 millionyears
ago, with some signs that dinosaurs in particular were already in a slow decline in the late
Cretaceous.What’smore,volcanicactivityisfrequentonthisplanetandisaplausible culpritfor
otherancientextinctions,whilegiant meteorstrikesare muchmore rare. Thisall makessense,
supporters say, if ongoing volcanic eruptions were the root cause of the world-wide K-Pg
extinctions.