Leonard David's INSIDE OUTER SPACE

Credit: NOVA

Noted asteroid expert, Clark Chapman, a senior scientist (retired) from the Southwest Research Institute in Boulder, Colorado, has assessed a recent NOVA broadcast that had Sir David Attenborough guiding viewers on a search for clues that could provide an unprecedented snapshot of what happened in the dinosaurs’ final moments on Earth.

The evening of 5/11/2022 “Nova” (WGBH) broadcast a two-hour special, narrated by David Attenborough, telling a “Just So” story about the “last day” of the Cretaceous period.  This was first published in the March 29, 2019 issue of The New Yorker.   An introduction had been published in the Proceedings of the National Academy of Sciences, but the promised follow-on peer-reviewed articles with actual evidence have not been published yet, so far as I can tell.  (A “Scientific Reports” article published this past December tries to deduce the season of the impact (spring), but shies away from demonstrating any paleontological evidence about what happened on the “last day.”)   Despite lack of peer-reviewed focus on the “last day,” this didn’t stop the BBC and now PBS from giving a high profile to this story (e.g. front-page story in a recent Washington Post story).

Amateur paleontologists to credible professionals

The first hour of Nova doesn’t even get to the day that Chicxulub was formed.  Although there are brief segments showing an artist’s poor conception of an asteroid heading toward Earth, it doesn’t arrive until the second hour.  When asteroid astronomy is briefly mentioned, it is done badly.  The graphics have it first nearly hitting Mars, which is pure fiction.  Most of the words and all of the graphics show that Near-Earth Asteroids are bumped into Earth-approaching orbits when they collide with each other, although Jupiter’s gravity is briefly mentioned.

European Space Agency astronaut Tim Peake took this image from the International Space Station of the Yucatan Peninsula – site of the Chicxulub impact crater.
Credit: Tim Peake/ESA/NASA

The first hour is devoted to paleontological work in the Hell Creek formation in North Dakota, where dinosaur fossils have been discovered for over a century.  It shows Robert DePalma and associates scraping away in the mud and finding petrified animal bones and skin.  Meanwhile, Attenborough narrates fancy graphics showing dinosaurs walking around in a rain-forest landscape.  DePalma was an amateur paleontologist, who became a belated graduate student during most of his studies.  There are about a dozen other commentators during the two-hours, ranging from another amateur paleontologist to credible professionals in several fields, most of them sticking to their areas of expertise without explicitly endorsing the “last day” story. 

For instance, Cathy Plesko of Los Alamos Natl. Lab talks about results of her numerical modeling of giant impacts.  There are limits to what can be gleaned from paleontological studies and Attenborough’s script strays far into the realm of speculation.  We are told that certain male dinosaurs were “loners”, that some probably dug in sandy soils for roots, and that another species generally laid two eggs at once (despite an earlier explanation that the number of fossilized dinosaur eggs found worldwide number little more than half-a-dozen).  Some paleontologists and archaeologists love to speculate on stories beyond what can be robustly proved by analysis of their excavations, and that was the tone of the first hour’s script.

Minimal evidence

The last half of the second hour was all about the general worldwide environmental horrors during the minutes, days, and months following the impact.  There were extravagant graphics and videos depicting scenarios that have been discussed for decades…little was new here, though there was an unusual emphasis on the far-flung effects of seismicity.

It was the first half of the second hour where the focus was on “the last day,” and purported evidence (and dramatic artistic videos) of what might have happened to individual animals that wound up dying on that day and later fossilized. 

One wishes that the evidence would be published in a scientific journal, because one cannot expect a popularized documentary to go into the necessary detail.  But it struck me as being minimal evidence and extremely unlikely to be true.  The chief evidence seems to be some tiny spherules caught in a petrified fish’s gills.  Of course, the Cretaceous–Paleogene( K/Pg) boundary layer is made up of such spherules, but they also result from meteorite falls all the time.  And spherules are produced by volcanic and industrial processes, among others.  The proponents of “the last day” hypothesis are clearly hoping to find a dinosaur that died on the day of the impact.  They find a plausible specimen, they think, but finally conclude that it probably died weeks or months earlier.  Given that dating of the K/Pg event has an uncertainty of tens of thousands of years (as one commentator on the program mentions), there’s no reason to think that the particular dinosaur didn’t die 30,000 weeks before the final day.

Credit: NASA/Don Davis

One spherule contains a tiny inclusion that is rich in iron and nickel.  It is offered as proof that the spherule contains an unmelted particle from the asteroid that struck on that day.  Earlier in the program, it is stated that a carbonaceous asteroid created Chicxulub, and carbonaceous chondrites typically contain only a few percent of siderophile material.  Regardless, while iron-rich material is consistent with many meteorite compositions, it is hardly proof of extraterrestrial origin.  A diagram is briefly shown that suggests that spherules in Hell Creek have the same compositions as known K/Pg spherules.  The context and origin of the diagram aren’t shown, but it is hardly surprising that such spherules are in Hell Creek.  One video actually shows a small animal (a contemporary mouse?) crawling out of an exposure of the K/Pg boundary layer in Hell Creek.

Public fascination

All of this may not be important, despite public fascination with “the last day.” For sure there was a last day, even though it can’t be timed within tens-of-thousands of years.  And it isn’t known what fraction of animals and plants were killed on that day worldwide (or in North Dakota), nor how many weeks or decades it took for whole species to be rendered extinct.There may have been a tsunami or otherwise turbulent waters in North Dakota that day, to account for evidence of “tumbled” fossils, but then there are many large thunderstorms every year, and many giant floods every century (like the Red River Flood in 1997), in North Dakota.  I consider the “Just So” story to be “possible” but extremely unlikely.  I have to admit that editors of Attenborough’s script seem to have ensured that nothing about the “last day” is said to be a certain fact.  Attenborough often uses words like “possible”, “likely”, “might have”, and so on.  And one commentator repeatedly cautions the viewers that science has “uncertainties.”  But the impression the viewer is left with, after the two hours of being awed by all the Computer Generated Imagery (CGI) of dinosaurs, is that the whole “last day” story has a fifty-fifty, or similar, chance of being true, whereas it seems to me to have an extremely tiny probability of being true from the evidence so far presented.

— Review by Clark Chapman