December 3. Recovery from extinction

To begin today I want to mention a new podcast I’ve just found out about, called Evolution Talk. It just began in August 2014 and as the title suggests, it’s all about evolution, including Darwin and other scientists that formulated the theory. It’s produced by Rick Coste on a weekly schedule, and I recommend it to you. It’s on iTunes, and I have a link on my blog to it as well. You can find information at EvolutionTalk.

Today’s topic is the recovery from the extinction at the end of the Cretaceous. Some of the great extinctions in earth history clearly impacted the planet for a long time. The Permian extinction in particular, together with the single-continent nature of Pangaea, seems to have resulted in an early Triassic that was pretty antagonistic for life for a few million years, at least. 

Life seems to have recovered from the end-Cretaceous event relatively quickly, which intuitively could be seen to support the idea of a very specific event, the asteroid impact, as the primary cause. 

One study led by researchers at MIT even suggests that the recovery of oceanic algae and cyanobacteria was underway as soon as just 100 years after the impact. Since those microorganisms are the base of the food chain, their recovery would have paved the way for the expansion of other life as well, but if you look at the recovery in other ways, it may have taken more time, even much more, a typical million years or so. 

The argument has been made that survivors were animals that could forage on dead plant or animal matter – which was presumably in abundance – rather than those that fed on living plants. A study of the interlinked recovery of plants and insects, led by researchers at Penn State, found that plant diversity was very low for 800,000 years after the extinction event, and for 8 million years, generally, plants and insects remained relatively low in diversity. But there were some exceptions where plants and bugs thrived, quite early in the Paleocene, the epoch immediately after the extinction. That kind of makes sense to me, that there might have been refuges, or locations where the devastation was not so intense, that could maintain or re-develop their diversity relatively quickly.

However long the recovery took, it certainly did happen. As the phytoplankton in the oceans recovered, so did the surviving bony fishes. On land in the course of the 10 million years after the extinction, the Paleocene epoch, mammals and birds both diversified and became larger than their Cretaceous ancestors. It would appear that being small was no longer such an advantage, with the big predatory dinosaurs gone. By the end of the Paleocene, 56 million years ago, and into the following Eocene Epoch, some flightless birds were growing to six feet in height. Mammals mostly were still small compared to later in the Cenozoic, but there were several different mammals that reached a meter or more in length. I think it is clear that they were getting bigger, and we’ll talk about some of the mammals and birds of the Cenozoic later this month.

I have links below to reports on the nature of the recovery from the end-Cretaceous extinction.

—Richard I. Gibson

LINKS:
Chaotic recovery?

Fish diversify
Rapid recovery? 
Recovery intervals
Recovery dynamics 
Paleocene mammals 

December 2. Cenozoic Time

The Tertiary and Quaternary, the original periods of the Cenozoic, were divided into epochs by Charles Lyell in 1833, and the names he gave are still retained, although they are now assigned to the Paleogene, Neogene, and Quaternary Periods. 

He used the same root word, “cene,” meaning recent, that is the prefix of the era, Cenozoic, but Lyell used it as a suffix when he named the epochs. He had analyzed assemblages of fossils from the different Cenozoic formations, and using the percentages of species that still were alive at present, he assigned names to the time periods that were marked by increasingly modern or recent fossil assemblages. He named the Eocene, which means “dawn-recent,” for rocks with fewer than 5% of modern species present, Miocene, “less recent,” for those that had 20-40% of modern species, and Pliocene, “more recent,” for those that were 40% to 90% modern. Since Lyell’s time, we’ve added Paleocene, “ancient-recent,” with essentially no modern species, Oligocene, “little or few-recent,” Pleistocene, “most recent,” and Holocene, “entirely recent.”

In order from oldest to youngest, the epochs are Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene. There’s been a lot of discussion about naming a new epoch, the Anthropocene, which means “human-recent,” for the last few thousand years, but the Holocene is only about the past 12,000 years so there would be considerable overlap. In my opinion it’s all semantics and preference and doesn’t matter.

The Paleocene, which began with the end of the Cretaceous, and the Eocene and Oligocene make up the Paleogene Period. The Miocene and Pliocene are the Neogene Period, and the Pleistocene and Holocene are the epochs of the Quaternary Period. The boundary between the Paleogene and Neogene is put at 23 million years ago, and the Quaternary started 2.5 million years ago and basically coincides with the glacial age.

So, that makes the Paleogene about 43 million years long, pretty typical for a geological period, and the Neogene is 21 million years long, which is on the short side. The Quaternary, at 2.5 million years, is an exceedingly short time span for a period, but it’s OK because we know so much about it, and because it does represent a time when things changed a lot, the modern ice ages. There is some argument as to whether the Quaternary should be seen as a full-fledged period or should be an epoch of the Neogene. All semantics and technicalities. For now I’m going with what I perceive to be the internationally recognized scheme that has the Quaternary as a period, not that it really matters.

I realize that that’s a lot of jargon and detail. I’ll try over the course of the month when I use names like Oligocene or whatever to keep it clear where we are as we progress through the Cenozoic.

Bret Harte

Let me close with a poem by Bret Harte, author and poet of the California Gold Rush. His poem, To the Pliocene Skull, was written in response to reports in the daily press of 1868: "A human skull has been found in California, in the pliocene formation. This skull is the remnant not only of the earliest pioneer of this State, but the oldest known human being. The skull was found in a shaft 150 feet deep, two miles from Angels in Calaveras County, by a miner named James Watson, who gave it to Mr. Scribner, a merchant, who gave it to Dr. Jones, who sent it to the State Geological Survey. . . . The published volume of the State Survey of the Geology of California states that man existed here contemporaneously with the mastodon, but this fossil proves that he was here before the mastodon was known to exist.” Harte was clearly skeptical of this discovery, and rightfully so.

To the Pliocene Skull – by Bret Harte

(A GEOLOGICAL ADDRESS)

Speak, O man, less recent!  Fragmentary fossil!
Primal pioneer of pliocene formation,
Hid in lowest drifts below the earliest stratum
Of volcanic tufa!

Older than the beasts, the oldest Palaeotherium;
Older than the trees, the oldest Cryptogami;
Older than the hills, those infantile eruptions
Of earth's epidermis!

Eo--Mio--Plio--whatsoe'er the 'cene' was
That those vacant sockets filled with awe and wonder,--
Whether shores Devonian or Silurian beaches,--
Tell us thy strange story!

Or has the professor slightly antedated
By some thousand years thy advent on this planet,
Giving thee an air that's somewhat better fitted
For cold-blooded creatures?

Wert thou true spectator of that mighty forest
When above thy head the stately Sigillaria
Reared its columned trunks in that remote and distant
Carboniferous epoch?

Tell us of that scene,-- the dim and watery woodland,
Songless, silent, hushed, with never bird or insect,
Veiled with spreading fronds and screened with tall club mosses,
Lycopodiacea,--

When beside thee walked the solemn Plesiosaurus,
And around thee crept the festive Ichthyosaurus,
While from time to time above thee flew and circled
Cheerful Pterodactyls.

Tell us of thy food,--those half-marine refections,
Crinoids on the shell and Brachipods au naturel,--
Cuttlefish to which the pieuvre of Victor Hugo
Seems a periwinkle.

Speak, thou awful vestige of the earth's creation,
Solitary fragment of remains organic!
Tell the wondrous secret of thy past existence,--
Speak! thou oldest primate!

Even as I gazed, a thrill of the maxilla,
And a lateral movement of the condyloid process,
With post-pliocene sounds of healthy mastication,
Ground the teeth together.

And from that imperfect dental exhibition,
Stained with express juices of the weed nicotian,
Came these hollow accents, blent with softer murmurs
Of expectoration:

"Which my name is Bowers, and my crust was busted
Falling down a shaft in Calaveras County;
But I'd take it kindly if you'd send the pieces
Home to old Missouri!"

—Richard I. Gibson

Cenozoic nomenclature 
Bret Harte photo in public domain
Time scale by Richard Gibson

December 1. The Cenozoic begins

Giovanni Arduino

The most recent 66 million years of earth history is the Cenozoic Era. Cenozoic comes from “cene” for “new” or “recent” plus “zoic” for “life,” in comparison to the Paleozoic, ancient life, and Mesozoic, middle life. The big subdivisions of earth history, the eras, came into common use about the start of the 19th Century. The first scheme, devised by Italian scientist Giovanni Arduino in the 1750s, subdivided the rocks into Primary, Secondary, and Tertiary, coinciding more or less with the Precambrian, Paleozoic, and Mesozoic and later rocks. The fourth grand division following the numerical scheme, Quaternary, was added in 1830 to account for the very recent glacial deposits found in Europe.

As the terms Precambrian, Paleozoic, and Mesozoic came into use in the early 1800s, the Primary and Secondary names were abandoned, but Tertiary and Quaternary were retained as periods of the Cenozoic Era. It took a long time for geology to outgrow the early terminology – it wasn’t until 2004 that the Tertiary was officially abandoned by international agreement. And now, the Cenozoic is divided into three periods – the older Paleogene and the more recent Neogene, whose names mean “ancient things” and “new things,” respectively, plus the Quaternary, an anachronistic name still retained. The Quaternary includes the present day. Because the changes in nomenclature are so recent, I can guarantee that you’ll still find lots of references to the Tertiary, and I’ll probably use it too. I’ll talk a bit more about additional subdivisions of Cenozoic time tomorrow.

Because the Cenozoic is so recent, the past 66 million years, we have a relatively good handle on it in terms of events, life, evolution, and timing, so it makes sense to have closely defined subdivisions. And because we do know so much about it, it also makes it a little harder for me to decide on which 31 topics to cover this month. But we’ll manage.

I want to remind you again of the scale of our journey, and the fact that it’s not a proper scale. The entire Cenozoic, 66 million years, which we’ll cover this month, is less than 1.5% of all earth history. To do this at the correct scale, the entire Cenozoic would have to be squeezed into the last five days of December.

—Richard I. Gibson

Image of Arduino in public domain