Silurian

On the other hand, the prevalence of very early life forms was singular in the highest degree.

Though the limestone formation was, on the evidence of such typical embedded fossils as ventriculites, positively and unmistakably Comanchean and not a particle earlier, the free fragments in the hollow space included a surprising proportion from organisms hitherto considered as peculiar to far older periods, even rudimentary fishes, mollusks, and corals as remote as the Silurian or Ordovician.

The inevitable inference was that in this part of the world there had been a remarkable and unique degree of continuity between the life of over three hundred million years ago and that of only thirty million years ago.

How far this continuity had extended beyond the Oligocene age when the cavern was closed was, of course, past all speculation.

This happened at the end of the Ordovician period.

It extends from about 460 to about 420 million years ago, Ordovician into the Silurian, and this is th- this is commonly cited as the likely cause of the Ordovician mass extinction event.

Yeah.

We talked about that in Episode 85.

fault.Mm-hmm

New York also has a lot of uplift.

So today, New York, there are a lot of really good fossil localities in New York, but they tend to be Devonian and Silurian.

They tend to be-

It remains to inquire whether the alterations, which the geologist can prove to have actually taken place at former periods in the geographical features of the northern hemisphere, coincide in their nature and in the time of their occurrence with such revolutions in climate as might naturally have resulted, according to the meteorological principles already explained.

Period of the primary fossiliferous rocks The oldest system of strata which afford by their organic remains any evidence as to climate or the former position of land and sea are those formerly known as the transition rocks or what have since been termed lower Silurian or primary fossiliferous formations.

These have been found in England, France, Germany, Sweden, Russia and other parts of central and northern Europe as also in the great lake district of Canada and the United States.

The multilocular or chambered univalves including the nautilus and the corals obtained from the limestones of these ancient groups have been compared to forms now most largely developed in tropical seas.

Another point of resemblance between the flora of New Zealand and that of the ancient carboniferous period is the prevalence of the fir tribe or of coniferous wood.

An argument of some weight in corroboration of the theory above explained respecting the geographical condition of the temperate and arctic latitudes of the northern hemisphere in the carboniferous period may also be derived from an examination of those groups of strata which immediately preceded the coal.

The fossils of the Devonian and Silurian strata in Europe and North America have led to the conclusion that they were formed for the most part in deep seas far from land.

In those older strata, land plants are almost as rare as they are abundant or universal in the coal measures.

It would cause massive DNA damage to any surface-dwelling organisms, resulting in global ecological collapse and a mass extinction event.

We actually suspect that at least one major mass extinction in Earth's history, the Ordovician-Silurian extinction around four hundred and forty million years ago, may have been triggered by a distant gamma ray burst striking our atmosphere.

Wait, really? It might have actually happened to Earth already.

It's a leading theory, yes.

Washed down from unknown jungles of mesozoic tree-ferns and fungi, and forests of tertiary cycads, fan-palms, and primitive angiosperms, this osseous medley contained representatives of more cretaceous eocene and other animal specimens than the greatest paleontologists could have counted or classified in a year mollusks crustacean armor fishes amphibians reptiles birds and early mammals great and small known and unknown no wonder gedney ran back to the camp shouting and no wonder everyone else dropped work and rushed headlong through the biting cold to where the tall derrick marked a new-found gateway to secrets of inner earth and vanished aeons when lake had satisfied the first keen edge of his curiosity he scribbled a message in his notebook and had young moulton run back to the camp to dispatch it by wireless This was my first word of the discovery, and it told of the identification of early shells, bones and ganoids, and placoderms, remnants of labyrinthodonts and thecodonts, great mossosaur skull fragments, dinosaur vertebrae and armor plates, pterodactyl teeth and wing bones, archiepteryx debris, miocene shark's teeth, primitive bird skulls, and skulls vertebrae and other bones of archaic mammals such as paleotheres xiphodons dinoceroses eohippe oreodons and titanotheres there was nothing as recent as a mastodon elephant true camel deer or bovine animal hence lake concluded that the last deposits had occurred during the oligocene age and that the hollowed stratum had lain its present dry dead and inaccessible state for at least thirty million years On the other hand, the prevalence of very early lifeforms was singular in the highest degree.

Though the limestone formation was, on the evidence of such typical embedded fossils as ventriculites, positively and unmistakably Comanchian and not a particle earlier, the free fragments in the hollow space included a surprising proportion from organisms hitherto considered as peculiar to far older periods, even rudimentary fishes, mollusks, and corals, as remote as the Silurian or Ordovician.

the inevitable inference was that in this part of the world there had been a remarkable and unique degree of continuity between the life of over three hundred million years ago and that of only thirty million years ago How far this continuity had extended beyond the Oligocene age when the cavern was closed was, of course, past all speculation.

In any event, the coming of the frightful ice in the Pleistocene some 500,000 years ago, a mere yesterday as compared with the age of this cavity, must have put an end to any of the primal forms which had locally managed to outlive their common terms.

And of course, geologists give all of these different geological systems all of these different names.

Cambrian, Ordovician, Silurian, and so on.

Yes.

And so what we were seeing here at Hunstanton belonged to just a part of that fossil record.

I am sure I did trouble my head about them.

Pliocene, Miocene, Eocene, Cretaceous, Jurassic, Triassic, Permian, Carboniferous, Devonian, Silurian, or primitive was all one to me.

But the professor, no doubt, was pursuing his observations or taking notes, for in one of our halts he said to me, "The farther I go, the more confidence I feel.

The order of these volcanic formations affords the strongest confirmation to the series of Davy.

Solid rock was appearing in the place of the lava coating.

The mass was composed of inclined and sometimes vertical strata.

We were passing through rocks of the transition or Silurian system.

It is evident, I cried, the marine deposits formed in the second period, these shales, limestones, and sandstones.