Tag: miocene

The song of ice and diatoms

In a previous post on this lethargic blog, I briefly touched the Antarctic extinction, the mass extinction of the fauna and flora inhabiting a whole continent, reduced to a desert of ice.

As is too often happens, I worried myself only about the macroscopic biota, and lazily forgot the microscopic lifeforms. Luckly, scientists are smarter than I am. Eveline Pinseel and coworkers have now described, in a paper on Science Advances, what happened to some of the most iconic microbial taxons – diatoms – that inhabited Antarctica (I have to thank Sylvie Coyaud for bringing this to my attention). Diatoms are special for many reasons, but mainly as being an example of microorganism with incredibly beautiful and unique shells, that readily fossilize and can be classified into prehistoric species and genera, something that it is hardly possible with many other unicellular beings (a notable exception are foraminiferans).

Extant Southern hemisphere diatoms and their extinct relatives, from Eveline et al. 2021

The study shows that in the Miocene (14-15 millions of years ago) Antarctic lakes had a rich diatom flora, with unique species so far unknown to science, but strongly related to those now present in New Zealand, Tasmania; and was overall not unlike the flora present in the contemporary Arctic. Temperatures, now hovering around -12° C, were around +5 °C at the time.

Then, the ice came. In the Pleistocene, about 150.000 years ago, the climate of Antarctica was much similar to today and, correspondingly, diatoms were much less diverse than in the Miocene, but still more diverse than today. The last glacial period was the final hammer for the Antarctic diatom flora: more diatom species were wiped out, not unlike the mammoths, or were confined to sub-Antarctic realms. The diatoms of today’s Antarctica land are a relict of what was once a diverse flora, adapted to some of the harshest conditions on Earth.

According to the authors

Although there are multiple records of regional extinctions and species turnover of lacustrine diatoms in Quaternary paleorecords of the Northern (60) and Southern (61) Hemisphere, the scale of the extinction of diatoms in continental Antarctica since the mid-Miocene is, both at the species- and genus-level, beyond anything reported in the literature thus far.

In other words, the Antarctic extinction was also the most profound mass extinction of diatoms known stodayo far. Their fate was most probably shared by large parts of the Antarctic microflora, of which we cannot say anything only because they didn’t leave shells to fossilize. Mass extinctions ,therefore, events reshape biodiversity at all levels. This is not news per se, we know that for example the end-Cretaceous extinction led to the extinction of numerous foraminiferan species. But it is a somber reminder of how much biodiversity has been lost forever, how much is going lost now, without us even noticing, without us being even able to interpret what such a loss would mean for other lifeforms.

The paper is: Eveline Pinseel et al. “Extinction of austral diatoms in response to large-scale climate dynamics in Antarctica”, Science Advances, Volume 7, Issue 38, 15 September 2021, https://doi.org/10.1126/sciadv.abh3233

The continent that died

Antarctica is now the closest thing on Earth we have to another world: a barren continent almost entirely covered in miles-thick ice, with temperatures going below -80° and practically devoid of macroscopic life once you go beyond the coast.

It wasn’t always so.

Yesterday night I was reading the a bit outdated but still amazing The Origin and Evolution of Mammals by T.S.Kemp and my jaw dropped to the floor when I stumbled on the following sentence:

“Needless to say” but oh dear, that’s when the obvious slaps you in the face, and it needs to be said. For tens or hundreds of millions of years Antarctica was a living, flourishing continent like the others, covered in forests, teeming with life. Right before the ice came, Antarctica looked like this:

Picture from Reguero et al. “Antarctic Peninsula and South America (Patagonia) Paleogene terrestrial faunas and environments: biogeographic relationships” Palaeogeography, Palaeoclimatology, Palaeoecology 179:3-4 (2002) https://doi.org/10.1016/S0031-0182(01)00417-5

I will have to dig deeper into this subject, that I suspect deserving a book (if one isn’t already there), and now I have no time to detail why and how it happened. But just let that sink in: The death of Antarctica is one of the main tragedies of the biosphere in the last 66 million years. Imagine if tomorrow Europe or South America, with all their life forms, their forests, their rivers, the singing of birds and the buzzing of bees, if all of that simply disappeared. That is what happened between 45 and 34 millions of years ago. Ice started to build up in the middle Eocene, and by the end of the period it was a frozen desert.

Imagine the slow death: a cap of ice every year slowly crawling from the core of the continent towards the coasts, animals and plants pushed to the edges, the winters every year more freezing, the summers every year shorter, until the ice reached the sea and there isn’t anywhere else to go. The penguins are basically the only survivors of this tragedy, relicts of a rich ecosystem.

What happened to Antarctica was an extinction of major proportions, but confined to a specific continent. Was it a mass extinction? Perhaps we need more categories, we need to start a taxonomy of extinction events. I will think about it. But for now, just remember: every time you see the beautiful glaciers and icebergs of Antarctica, you are witnessing the grim burial of an entire continent full of life, that was and now is gone.

 

The hidden bombardment

Earth is very good at cosmetics: it quickly and efficiently covers its scars. The Chicxulub impact that wiped out the Cretaceous was one of the largest impact events in the last hundred million years in the Solar System, and yet it left no visible trace today, save for an arc of carsic structures known as cenotes in the Yucatan Peninsula. We had to dig deep and hard to find it. So it is no surprise that new impact events are still being found. Nozaki et al. now declare on Scientific Reports to have found 11 million years old ejecta in the sediments of the North Pacific. Ejecta, mind you, not the crater. That is unknown yet.

We managed to link only one mass extinction to asteroid impact. That might be the case. But impacts have been (and will be) a constant in Earth history. While globally catastrophic impacts are rare, what about locally catastrophic ones? They must have had important ecological consequences. A region-devastating impact can still alterate weather patterns and radically steer the direction of life history. A promising but localized lineage can be wiped off, a destroyed area can be re1populated and lead to speciation, and so on. Our past must have been sculpted by many more fatal days than the one at Chicxulub, and we still have almost no idea.