Since we already know from the previous post titled "A journey into the deep past" that our Michelinoceras swam somewhere between Pomerania and Scandinavia, let us try to specify the place in that realm where in the period between 460 and 420 million years ago there was a shallow, warm sea where those creatures usually lived. And we certainly would not mean the Baltic Sea, as this is one of the youngest seas on Earth which originated no sooner than twelve thousand years ago. No to mention the fact that in the place of the present Baltic Sea immense fresh water lake was appearing after the end of each glacial age, as a result of melting glacier. The last period when such ephemeral lakes occurred was 130-115 thousand years ago.
We should say in the first place that the Earth crust has been in constant movement throughout its history. The tectonic plates carrying continents interact and shift together, as a result of magma circulation inside the Earth. The magma comes out to the surface of the lithosphere in the so called rift zones. The following diagram taken from the interesting blog "Tectonic Tour" well reflects the process of splitting the continental crust and of moving two continents away.
The present pattern of oceans and continents has been around for “barely” 15 million years but it changes slowly all the time. For example, North America moves away from Europe at a yearly path of 2.5 cm, and the crust under the Massovian land sinks 1 mm every year, whereas on the other side of the Baltic Sea, in Swedish Scania, it raises 1.5 mm a year. From the perspective of the length of human life a yearly change of one millimeter in the earth's movement is rather unnoticeable. Similarly, a period of 60.000 years is like an eye blink from the time perspective of Earth. Such a period would be needed for the Baltic Sea to come over to the doorstep of Massov, now being 62 km away from the sea. Actually, it may happen even earlier, if one considers global warming and an ensuing rise of water level in the oceans.
Perhaps, the perspective of the time span of a generation to which we usuall limit our reflections on consequences of our actions, impedes our understanding that we may induce the acceleration of certain processes on Earth which in the future could be detrimental to human life or to life in general. Or possibly, the skeptics are right who say that the forces of nature are too mighty for human actions to have any important meaning and that the Earth would evolve accordingly to the natural forces, irrespectively of the human activity. Let us return to the history of the Earth, on the example of the Massovian land and to the place and time of birth of our cephalopod.
Let’s take a look at the above Wiki map of the world from the Ordovician period, when the Orthocerida order separated itself from the older cephalopods, possibly from the family of Baltoceratidae. We can see that the layout of continents and oceans was quite different than nowadays. All lands in that period were nothing but bare rocks, sands and muds, with some pattern of arid rivers and lakes. There were first signs of life – the mosses, appearing now and then, alongside the brackish watersides. All animals still lived in the seas, and the first bone fish (Osteichthyes) was then the highest developed creature on Earth. There was in the Ordovician one supercontinent named Gondwana (which combined the present-day Africa, southern Europe, South America, Australia, India and Antarctica), and few other, smaller proto-continents: Laurentia (the current North America and Greenland), Baltica (Scandinavia, northern parts of Russian and the Polish Planes), Siberia, Avalonia and other pieces of land.
We are especially interested in Avalonia, because many facts indicate that the most part of present-day Pomerania rests on the once Avalonian plate. The Massovian land, submerged in the sea and located not far away from the South Pole, was marked on the map by a red dot. One may assume that at such latitudes the Orthoceridas would not enjoy optimal living conditions, due to cold waters, scarce sunshine and thus not abundant plankton, a prime menu for the ocean shelf creatures. Baltica, situated more to the North and closer to the Equator, seemed to be a more livable place to our Michelinoceras. The scientists' hypothesis that it originated from Scandinavia could also be backed up by the fact that Baltica and Avalonia were separated at that time by a two-to-three-kilometer deep seabed which could not be crossed by shelf animals, who were not very good swimmers. Its hypothetical place of birth was marked on the above map of world by a green dot (I shall return to this later).
In the Silurian period (the map comes from the Wiki) that is about 440 million years ago, Avalonia “caught up” with Baltica, docked to her and formed a common foundation of the continental plate which tied up Pomerania with Scandinavia and the north-eastern part of Poland. The binding of the two proto-continents was followed in the same Silurian period by the collision of Laurentia with Baltica and some time later, with Avalonia. A new super-continent was born, named Laurussia, extending from today’s Ural Mountains till today’s Rocky Mountains (both of those mountain ranges were formed much later).
Please draw your attention to the fact that the Avalonian craton (or a part of the newly formed continental plate), apart from Pomerania on its eastern tip, comprised also today’s Lower Saxony, Benelux, England, southern Ireland, Canadian Newfoundland and the U.S. state of Massachusetts! All these lands have a common rock foundation originating from the Ordovician and Silurian periods. We are talking about the deepest layer of the Earth's crust which for example under the Massovian land reaches depth of 35 km. Oceanic crust is much thinner, normally about 5-7 km thick. The so called mantle convection, or a slow circulation of the Earth's heat from its center to the surface, breaks the Earth's crust in its thin ocean layers. The magma released from the mantle forms mid-ocean ridges, what is well depicted by the following animation.
The continous process of the magma release along the mid-ocean rings, being a tectonic plate boundary, pushes the plates away, so that they move under another tectonic plate in the so called subduction zone. That's the way the continents "wander" on the surface of the asthenosphere, the upper part of the Earth's mantle. Here is an interesting diagram depicting the forces which make the continents moving, published on the site SMSTsunami Warning.
The crust is just above a colder part of the Earth called the mantle (about +700° C) which reaches a depth of about 100 km. And deeper under there is the so called asthenosphere, consisting of a semi-liquid magma of a temperature reaching about +1600°C. We shall not be stepping down lower … With the laps of time (measured in millions of years) the oldest rocks were successively covered by younger sedimentation layers, in accordance with subsequent geological periods. We shall talk about it in the next post.
We should say in the first place that the Earth crust has been in constant movement throughout its history. The tectonic plates carrying continents interact and shift together, as a result of magma circulation inside the Earth. The magma comes out to the surface of the lithosphere in the so called rift zones. The following diagram taken from the interesting blog "Tectonic Tour" well reflects the process of splitting the continental crust and of moving two continents away.
Perhaps, the perspective of the time span of a generation to which we usuall limit our reflections on consequences of our actions, impedes our understanding that we may induce the acceleration of certain processes on Earth which in the future could be detrimental to human life or to life in general. Or possibly, the skeptics are right who say that the forces of nature are too mighty for human actions to have any important meaning and that the Earth would evolve accordingly to the natural forces, irrespectively of the human activity. Let us return to the history of the Earth, on the example of the Massovian land and to the place and time of birth of our cephalopod.
Let’s take a look at the above Wiki map of the world from the Ordovician period, when the Orthocerida order separated itself from the older cephalopods, possibly from the family of Baltoceratidae. We can see that the layout of continents and oceans was quite different than nowadays. All lands in that period were nothing but bare rocks, sands and muds, with some pattern of arid rivers and lakes. There were first signs of life – the mosses, appearing now and then, alongside the brackish watersides. All animals still lived in the seas, and the first bone fish (Osteichthyes) was then the highest developed creature on Earth. There was in the Ordovician one supercontinent named Gondwana (which combined the present-day Africa, southern Europe, South America, Australia, India and Antarctica), and few other, smaller proto-continents: Laurentia (the current North America and Greenland), Baltica (Scandinavia, northern parts of Russian and the Polish Planes), Siberia, Avalonia and other pieces of land.
We are especially interested in Avalonia, because many facts indicate that the most part of present-day Pomerania rests on the once Avalonian plate. The Massovian land, submerged in the sea and located not far away from the South Pole, was marked on the map by a red dot. One may assume that at such latitudes the Orthoceridas would not enjoy optimal living conditions, due to cold waters, scarce sunshine and thus not abundant plankton, a prime menu for the ocean shelf creatures. Baltica, situated more to the North and closer to the Equator, seemed to be a more livable place to our Michelinoceras. The scientists' hypothesis that it originated from Scandinavia could also be backed up by the fact that Baltica and Avalonia were separated at that time by a two-to-three-kilometer deep seabed which could not be crossed by shelf animals, who were not very good swimmers. Its hypothetical place of birth was marked on the above map of world by a green dot (I shall return to this later).
In the Silurian period (the map comes from the Wiki) that is about 440 million years ago, Avalonia “caught up” with Baltica, docked to her and formed a common foundation of the continental plate which tied up Pomerania with Scandinavia and the north-eastern part of Poland. The binding of the two proto-continents was followed in the same Silurian period by the collision of Laurentia with Baltica and some time later, with Avalonia. A new super-continent was born, named Laurussia, extending from today’s Ural Mountains till today’s Rocky Mountains (both of those mountain ranges were formed much later).Please draw your attention to the fact that the Avalonian craton (or a part of the newly formed continental plate), apart from Pomerania on its eastern tip, comprised also today’s Lower Saxony, Benelux, England, southern Ireland, Canadian Newfoundland and the U.S. state of Massachusetts! All these lands have a common rock foundation originating from the Ordovician and Silurian periods. We are talking about the deepest layer of the Earth's crust which for example under the Massovian land reaches depth of 35 km. Oceanic crust is much thinner, normally about 5-7 km thick. The so called mantle convection, or a slow circulation of the Earth's heat from its center to the surface, breaks the Earth's crust in its thin ocean layers. The magma released from the mantle forms mid-ocean ridges, what is well depicted by the following animation.
The continous process of the magma release along the mid-ocean rings, being a tectonic plate boundary, pushes the plates away, so that they move under another tectonic plate in the so called subduction zone. That's the way the continents "wander" on the surface of the asthenosphere, the upper part of the Earth's mantle. Here is an interesting diagram depicting the forces which make the continents moving, published on the site SMSTsunami Warning.
Knowing already from the first
article ("A journey into the deep past") that "Massovian" michelinoceras
lived in the period 440-420 million years ago, let us return to the question of
the geographical place of its existence. After having examined the history of
the Pomeranian part of the continent, we can assume that this creature lived in
the vicinity of the today's island Gotland, Sweden. The last Weichselian glacier
took the fossiled orthocone of the specimen from there and laid on the Massovian
ground some fifteen thousand years ago. On the map originating from the paper
of Trond H. Torsvik and L. Robin M. Cocks "Norway in space and time: A Centennial
cavalcade" in the Norwegian Journal of Geology No. 85 of 2005, I marked with
yellow colour the route of transferring the fossil from the Gotland island to
Pomerania. I permitted myself to slightly adjust the course of the eastern
ridge of Avalonia.
As
you can see on the map, the area around Gotland from before 425
million years ago, was covered with shallow
subequatorial sea waters, wherein intensively
developing coral reefs ("bioherms") lived. The traveled distance
by the Michelinoceras is impressive! Although born in waters
of the continental shelf of
the newly-born palaeocontinent Laurussia,
also called Euramerica, in the vicinity of the future land Pomerania
(then still plunged deep in the ocean), the creature lived in the southern hemisphere.
Its
remains made a journey on the
globe from the latitude of about 15 degree South to the parallel of about 58 degree North. This
gives the distance in a straight
line of some 8,100 kilometers. In
fact, the route passed was much longer,
because the continental plate moved northwards a
kind of "scrolls". The
last 500-km stretch the fossil passed inside the
glacier to be laid down on the Pomeranian soil.
Equally impressive was the Michalinoceras journey through time.
He was born and lived about 430 million years ago. His remains were trapped in the Scandinavian Silurian limestone
sediment layer. The piece of rock
from the original layer was taken by the glacier about 27,000 years ago on its southward route
towards the present Poland. It has been kept another twelve thousand years in
the glacial body, until it was released fifteen thousand years ago on the
Massovian ground during the phase of the glacier’s retreat.
. 
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