Humans have long been fascinated by fossils and have interpreted them in many different ways. Some believed they were rocks decorated by a playful Creator, while others thought they were lasting traces of the biblical flood. Those who saw in fossils the world’s vanished organisms risked the disapproval of religious authorities who imposed their view of a single divine creation event on the natural world. Some even went so far as to believe that fossils were the work of the devil strewn among layers of rock to test the faithful.

The existence of fossilized species, or “lost species” after the expression used in France by Georges-Louis Leclerc Buffon (1707-1788), was an idea that gained popularity in the late 18th century. Early the next century, paleontologist and founder of comparative anatomy George Cuvier (1769-1832) concluded that the existence of numerous extinct forms did not necessarily imply evolution. Like Buffon and many others before him, Cuvier rejected the idea of “transformism” proposed by Jean-Baptiste-Pierre Lamarck (1744-1829). Instead, he militantly believed in the hypothesis—already in vogue for several decades&mdash Read More
Humans have long been fascinated by fossils and have interpreted them in many different ways. Some believed they were rocks decorated by a playful Creator, while others thought they were lasting traces of the biblical flood. Those who saw in fossils the world’s vanished organisms risked the disapproval of religious authorities who imposed their view of a single divine creation event on the natural world. Some even went so far as to believe that fossils were the work of the devil strewn among layers of rock to test the faithful.

The existence of fossilized species, or “lost species” after the expression used in France by Georges-Louis Leclerc Buffon (1707-1788), was an idea that gained popularity in the late 18th century. Early the next century, paleontologist and founder of comparative anatomy George Cuvier (1769-1832) concluded that the existence of numerous extinct forms did not necessarily imply evolution. Like Buffon and many others before him, Cuvier rejected the idea of “transformism” proposed by Jean-Baptiste-Pierre Lamarck (1744-1829). Instead, he militantly believed in the hypothesis—already in vogue for several decades—of a series of successive creation events separated by as many global extinctions.

Faced with repeated geological discoveries and mounting descriptions of “lost worlds”, the proponents of creationism were forced to dramatically increase the number of creation events. At one point, paleontologists Friedrich August von Quenstedt (1809-1889) of Germany and Alcide d’Orbigny (1802-1857) of France counted 27 creation events, meaning there would have been 26 “lost worlds” before ours!

The Earth of the Devonian Period, as reconstructed by today’s paleontologists, would have described as a “lost world” two centuries ago. It is an understandable interpretation, considering that the Devonian Earth was nothing like the planet we know. Not only were the living creatures unlike those of today, and the climate dramatically different, but even seen from space, the planet would hardly have been recognizable.

We now know that the history of Earth was not defined by a succession of lost and reborn worlds. It was, and remains, a world of gradual yet perpetual change, its appearance continually reshaped by geologic processes.

© Miguasha National Park 2007

<i>Mammut americanum</i>

In 1740, the Baron of Longueil, back from his trip to North America, presented the court of France with the strange animal bones that were found along the Ohio River: a femur, a tusk, and molars (shown here). Following several debates on the matter, the naturalist Buffon declared in 1778 that they were the remains of a “lost species”. The concept of a fossil was thus born from Mammut americanum – a North American species that appeared 3.75 million years ago and died out around 10,000 years ago.

The original specimen is kept at the Muséum National d’Histoire Naturelle in Paris.
2007
© Miguasha National Park


Our planet resembles a giant peach. If we could slice through such an enormous fruit, we would see that the peel is like the outer layer of rock on which we live, what geologists call the crust. The Earth’s crust is very thin, extending to depths of 30 to 65 km under the continents, and only 5 to 15 km under the oceans. Beneath the crust (or peel!) lies the Earth’s mantle, which is analogous to the juicy flesh of the peach. The mantle is made of hot rock that can flow slowly, just as you can deform peach flesh as you squeeze it in your fingers. Finally, hidden deep beneath the mantle at a depth of 2,885 km is the outer edge of the Earth’s iron-nickel core – the peach pit if you will! But the similarities end there. The inner core may be solid, but the outer part is hot metallic liquid – the only liquid layer in the planet.

Not all mantle rock can flow easily. The uppermost mantle, along with the thin crust, defines a fairly rigid layer known as the lithosphere. The lithosphere ranges from 10 to 250 km thick and is broken into fragments, called plates, which move around the Earth like pieces of a giant jigsaw puzzle.

Below the lit Read More
Our planet resembles a giant peach. If we could slice through such an enormous fruit, we would see that the peel is like the outer layer of rock on which we live, what geologists call the crust. The Earth’s crust is very thin, extending to depths of 30 to 65 km under the continents, and only 5 to 15 km under the oceans. Beneath the crust (or peel!) lies the Earth’s mantle, which is analogous to the juicy flesh of the peach. The mantle is made of hot rock that can flow slowly, just as you can deform peach flesh as you squeeze it in your fingers. Finally, hidden deep beneath the mantle at a depth of 2,885 km is the outer edge of the Earth’s iron-nickel core – the peach pit if you will! But the similarities end there. The inner core may be solid, but the outer part is hot metallic liquid – the only liquid layer in the planet.

Not all mantle rock can flow easily. The uppermost mantle, along with the thin crust, defines a fairly rigid layer known as the lithosphere. The lithosphere ranges from 10 to 250 km thick and is broken into fragments, called plates, which move around the Earth like pieces of a giant jigsaw puzzle.

Below the lithosphere, enormous heat creates convection cells in the deeper mantle. The stiff lithospheric plates are carried along by these currents of hot flowing rock, much like a conveyor belt. The movement is slow – not much faster than your fingernails grow – but over geologic time, the effect is very dramatic. As the plates move, they carry with them the parts that poke above the water – the continents and islands – and in so doing, constantly reshape the geography of our planet!

This activity, known as plate tectonics, has not been steady over time. Some periods were calmer; others, like the Devonian, much more intense. Where plates moved apart, oceans formed, and where they pushed against each other, continents collided and the towering majestic peaks of new mountain chains emerged from the disappearing Devonian seas...

© Miguasha National Park 2007

Video

4,57 billions years of evolution of our planet

The screen is divided into five sections, presenting the following items:

  • The main screen presents the drifting continents. The film begins 800 million years ago and ends today.
  • Screen 2 presents corresponding dates.
  • Screen 3 presents species present during the corresponding periods.
  • Screen 4 presents the average temperature during corresponding eras
  • Screen 5 presents corresponding periods according to the International Commission on Stratigraphy chart.
Year Species
740 m. years Algae and cyanobacteria
670 m. years Algae and cyanobacteria
610 m. years Algae and cyanobacteria
560 m. years Enigmatic soft-bodied animals
510 m. years Huge diversity of marine animals, several with hard body parts
460 m. years Strange fish swim the seas
410 m. years Flora and small invertebrates appear along the shores
350 m. years Tetrapods along the shores and the first great forests
310 m. years Small reptiles on earth and giant dragonflies in the air
260 m. years Huge reefs in the seas and more and more reptiles on earth
210 m. years Dinosaurs appear, as well as small mammals
160 m. years First feathered birds
130 m. years Bees and butterflies gather pollen from flowers
65 m. years Demise of the dinosaurs and great diversity of mammals
2 m. years Origins of man
15 000 years Modern man is on all continents
Year Temperature
740 m. years Very cold
670 m. years Very cold
610 m. years Very cold
560 m. years 19_C (warm)
510 m. years 20_C (warm)
460 m. years 23_C (warm)
410 m. years 21_C (warm)
350 m. years 16_C (cold)
310 m. years 10_C (cold)
260 m. years 16_C (warm)
210 m. years 19_C (warm)
160 m. years 20_C (warm)
130 m. years 20_C (warm)
65 m. years 17_C (warm)
2 m. years 15_C (cold)
15 000 years 16_C (cold)
Year Periods
740 m. years Proterozoic
670 m. years Proterozoic
610 m. years Proterozoic
560 m. years 542 Cambrian
510 m. years 542 Cambrian
460 m. years 488 Ordovician, 444 Silurian
410 m. years 416 Devonian
350 m. years 359 Mississippian
310 m. years 318 Pennsylvanian
260 m. years 299 Permian, 251 Triassic
210 m. years 200 Jurassic
160 m. years 146 Cretaceous
130 m. years 66 Paleogene
65 m. years 23 Neogene
2 m. years 1.8 Quaternary
15 000 years Quaternary

Moreover, the main screen indicates the location of Miguasha during all these years.

Miguasha National Park

© Miguasha National Park 2007


A geographic map of the world as it appeared during Devonian time would show a virtually unrecognizable planet. Most landmasses had joined together to form two large continents, and one of these, called Euramerica by geologists, straddled the equator and was spanned from north to south by a mountain chain in the final stages of formation. Euramerica and its impressive mountain chain were created when two landmasses, Laurentia and Baltica, collided. One of the many river systems draining these mountains flowed into the large Miguasha estuary.

The other large landmass, called Gondwana, occupied a good portion of the southern hemisphere and even covered the South Pole. It lay quite near the southern end of Euramerica, and the two finally collided in Upper Devonian time, closing the Rheic Ocean between them.

By 300 million years ago at the end of the Carboniferous Period, Euramerica and Gondwana had fused together to form a single supercontinent called Pangea. This supercontinent would later split apart and form the Atlantic Ocean. The event divided Euramerica’s mountain chain, and the two halves drifted apart, bordering either side of the expanding Atlanti Read More
A geographic map of the world as it appeared during Devonian time would show a virtually unrecognizable planet. Most landmasses had joined together to form two large continents, and one of these, called Euramerica by geologists, straddled the equator and was spanned from north to south by a mountain chain in the final stages of formation. Euramerica and its impressive mountain chain were created when two landmasses, Laurentia and Baltica, collided. One of the many river systems draining these mountains flowed into the large Miguasha estuary.

The other large landmass, called Gondwana, occupied a good portion of the southern hemisphere and even covered the South Pole. It lay quite near the southern end of Euramerica, and the two finally collided in Upper Devonian time, closing the Rheic Ocean between them.

By 300 million years ago at the end of the Carboniferous Period, Euramerica and Gondwana had fused together to form a single supercontinent called Pangea. This supercontinent would later split apart and form the Atlantic Ocean. The event divided Euramerica’s mountain chain, and the two halves drifted apart, bordering either side of the expanding Atlantic. Today, they are known as the Appalachian Mountains in North America, where they extend from Alabama to the island of Newfoundland, and the Caledonide Mountains on the other side of the Atlantic, where they are found in the British Isles, the Scottish Highlands, Norway, Sweden, and along the eastern margin of Greenland. On the western edge of the African continent, the Mauritanides were also part of this mountain building event.

The Appalachian Mountains were built up during the Devonian Period, when their peaks would have been much taller and sharper than they are today. Millions of years later, erosion has reduced them to rounded hills and valleys in the heart of the Gaspé, creating the impression of an undulating verdant sea.

© Miguasha National Park 2007

Location of the ancient estuary of Miguasha

During the Upper Devonian, the source of the ancient estuary originated in the young Appalachian Mountains newly formed at the southeastern boundaries of the continent of Euramerica. The position of the ancient continental landmasses is by Ron Blakey (http://jan.ucc.nau.edu/~rcb7

François Bienvenue
The position of the ancient continental landmasses is by Ron Blakey (http://jan.ucc.nau.edu/~rcb7)
2007
© Miguasha National Park, © Ron Blakey


During most of the Devonian Period, the climate was relatively mild and the continent of Euramerica, which straddled the equator at the time, set the scene for the spread of tropical and equatorial forests. The position of this land mass also meant that many communities of vertebrate animals were concentrated near the equator where the warm climate encouraged their growth and evolution.

But the end of the Devonian was marked by a period of global cooling, and severe glaciations caused the extinction of many species. This cooler period lasted for 100 million years until the beginning of the Triassic Period, when dinosaurs rose up to reign over the world.

The cooling episode may be partly explained by the emergence of photosynthetic plants in Earth’s first forests. Photosynthetic plants remove carbon dioxide – a greenhouse gas – from the atmosphere, and this may have contributed to the lower temperatures. But the “big chill” can also be explained by the positions of the continents themselves. With the major remodelling of a landmass like that involved in the formation of Pangea, oceans are closed and water currents drastically modi Read More
During most of the Devonian Period, the climate was relatively mild and the continent of Euramerica, which straddled the equator at the time, set the scene for the spread of tropical and equatorial forests. The position of this land mass also meant that many communities of vertebrate animals were concentrated near the equator where the warm climate encouraged their growth and evolution.

But the end of the Devonian was marked by a period of global cooling, and severe glaciations caused the extinction of many species. This cooler period lasted for 100 million years until the beginning of the Triassic Period, when dinosaurs rose up to reign over the world.

The cooling episode may be partly explained by the emergence of photosynthetic plants in Earth’s first forests. Photosynthetic plants remove carbon dioxide – a greenhouse gas – from the atmosphere, and this may have contributed to the lower temperatures. But the “big chill” can also be explained by the positions of the continents themselves. With the major remodelling of a landmass like that involved in the formation of Pangea, oceans are closed and water currents drastically modified. Ocean currents are important temperature regulators because they redistribute heat around the planet, so a change in ocean current circulation inevitably leads to a change in the climate.

© Miguasha National Park 2007

Atmospheric carbon curve

Variations in temperatures and atmospheric concentrations of carbon through geological time. A marked drop in the concentration of atmospheric carbon and rapid cooling characterized the end of the Devonian and the onset of the Carboniferous.

François Bienvenue
2007
© Miguasha National Park


Miguasha under the tropics!

Major climatic domains of the Upper Devonian. The region of Miguasha was situated south of the equator and benefited from a relatively warm climate. An ice cap associated with an overall decrease in temperatures formed at the South Pole at the end of the Devonian.

François Bienvenue
Position of the paleocontinents by C.R. Scotese (Paleomap Project, http://scotese.com).

© Miguasha National Park, © Paleomap Project


The fish of the Devonian Period experienced rather short days. We know that the Devonian year had 400 days, making each day only 22 hours long. This just goes to show that nothing is constant on Earth, not even the length of a day! Just as continents move and change direction, the speed at which our planet rotates also changes over time.

How is this possible? It is really the fault of the Moon, our celestial companion. Since it formed 4.2 billion years ago (4.2 Ga), the Moon has driven the tides on our planet. The Moon’s gravitational pull attracts great masses of water toward it while in orbit around us. As the Earth turns eastward, the tides move westward, and this phenomenon imperceptibly slows the rotation of our planet by 0.0016 seconds per century!

Our planet was therefore turning faster in the past, such that each year consisted of more, but shorter, days. Though the features of the Earth may change, the laws of physics are constant. In a binary system like the Earth and Moon, if one of the two companions loses momentum, the other must gain momentum. Over time, as Earth’s rotation slows, the orbital velocity of the Moon increases, forcing i Read More
The fish of the Devonian Period experienced rather short days. We know that the Devonian year had 400 days, making each day only 22 hours long. This just goes to show that nothing is constant on Earth, not even the length of a day! Just as continents move and change direction, the speed at which our planet rotates also changes over time.

How is this possible? It is really the fault of the Moon, our celestial companion. Since it formed 4.2 billion years ago (4.2 Ga), the Moon has driven the tides on our planet. The Moon’s gravitational pull attracts great masses of water toward it while in orbit around us. As the Earth turns eastward, the tides move westward, and this phenomenon imperceptibly slows the rotation of our planet by 0.0016 seconds per century!

Our planet was therefore turning faster in the past, such that each year consisted of more, but shorter, days. Though the features of the Earth may change, the laws of physics are constant. In a binary system like the Earth and Moon, if one of the two companions loses momentum, the other must gain momentum. Over time, as Earth’s rotation slows, the orbital velocity of the Moon increases, forcing it to gradually recede away from us. Using lasers, we have confirmed this movement and found it to be 3.8 centimetres per year. This may seem too small to make a real difference, but when added up over hundreds of millions of years, we can calculate that the Moon is now twice as far from Earth as it was during Devonian time. As a consequence, Devonian tides were up to seven times larger than today’s tides.

These physics calculations have been verified by paleontological discoveries. One line of evidence comes from corals. Corals, both living and fossilized, are animals that live inside little cups of calcium carbonate (calcite; CaCo3) that they themselves secrete. The coral “skeleton” grows because the animals deposit calcite every day they are alive. The activity temporarily stops at night because the animals live symbiotically with single-celled algae that need light to function. The daily layers are visible under a microscope, making it possible to count days, somewhat like counting tree rings to determine the passage of years.

Species that live in temperate waters are subjected to seasonal variations in temperature, so winter growth is slower and the marks farther apart. Years are therefore easily distinguished among the series of growth lines. A modern coral would show us years consisting of 365 lines.

Coral fossils living 400 million years ago (400 Ma) in the Early Devonian display years of 400 lines, and thus 400 days, proving that the Earth did indeed turn faster at that time. For corals that lived during the Upper Carboniferous (300 Ma), there are approximately 380 lines each year. The fossil record thus clearly demonstrates that Earth’s rotation has gradually slowed over time, and that it is still slowing down today.

© Miguasha National Park 2007

<i>Cylindrophyllum</i>

A colony of the rugose coral Cylindrophyllum. Cylindrophyllum were present in the Gaspé region at the beginning of Middle Devonian time. This specimen comes from the Battery Point Formation in central Gaspé.

Miguasha National Park
2001
© Miguasha National Park


Learning Objectives

The learner will:
  • identify and classify different types of fossils;
  • explain the stages of fossilization and the best conditions to create and preserve fossils;
  • make assumptions about the evolution of living beings;
  • make assumptions as to the explanation of the disappearance of some species.

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