Paleontology, the scientific study of fossils, is the union of two scientific disciplines.Discoveries in geology help us understand how different rock types formed and how they trapped the remains of dead organisms. Biology helps us deduce how these ancient beings lived, how they interacted with their ecosystems, and their position in the great evolutionary tree.

We find fossils in sedimentary rocks, meaning rocks derived from the accumulation of sediments (mud, clay, sand, gravel, etc.). The Escuminac sedimentary formation at Miguasha was the result of the weathering and erosion of the young Appalachian mountain chain, which loaded streams and rivers with silt and rock debris. Slowing their course as they approached sea level, the rivers deposited this sediment load into a large estuary. Within that watery realm, dying fish, plants and invertebrates settled to the estuary floor where they were rapidly covered with sediments. Others were buried alive by sudden slides of mud and sand. Whatever the means, burial initiated the process of fossilization.

Sediments are turned to rock when compacted under their own weight and subjected to various chemical processes. Read More
Paleontology, the scientific study of fossils, is the union of two scientific disciplines.Discoveries in geology help us understand how different rock types formed and how they trapped the remains of dead organisms. Biology helps us deduce how these ancient beings lived, how they interacted with their ecosystems, and their position in the great evolutionary tree.

We find fossils in sedimentary rocks, meaning rocks derived from the accumulation of sediments (mud, clay, sand, gravel, etc.). The Escuminac sedimentary formation at Miguasha was the result of the weathering and erosion of the young Appalachian mountain chain, which loaded streams and rivers with silt and rock debris. Slowing their course as they approached sea level, the rivers deposited this sediment load into a large estuary. Within that watery realm, dying fish, plants and invertebrates settled to the estuary floor where they were rapidly covered with sediments. Others were buried alive by sudden slides of mud and sand. Whatever the means, burial initiated the process of fossilization.

Sediments are turned to rock when compacted under their own weight and subjected to various chemical processes. After millions of years, tectonic movements can slowly raise the rocks of ocean floors, sometimes forming new mountains that will in turn be subjected to erosion. This cycle of “erosion–sedimentation–compaction” has been happening on Earth for as long as there have been solid rocks and liquid water to erode them; that is, for more than four billion years.

A fossil is the exception, rather than the rule. Normally, all that lives and dies decomposes and is reused by the next generation of living beings. Under certain conditions, however, the hardest parts of an organism (bones, teeth, spines, scales, shells, carapaces...) cannot decompose and rest entombed in sediments. Ideal conditions for fossil preservation are typically found at the bottom of oxygen-poor waters where some of the bacteria involved in decomposition cannot survive, thus leaving the hard remains intact. Other bacteria contribute to the fossilization process by turning soft tissue into minerals. As the sediments surrounding them become rock, chemical processes transform the creature’s remains so that they also resemble rocks.

Subjected once again to erosion, this time by the Ristigouche River, the rocks in Miguasha’s cliff reveal fossilized creatures that have lain dormant for 380 million years. Around the world, fossils like those at Miguasha represent valuable records of past life, teaching us about the prevailing conditions so very long ago and providing some of the most important evidence for the theory of evolution.

© Miguasha National Park 2007

The Process of Fossilization

The process of fossilization, illustrated here with the death of the dipnoan fish Fleurantia denticulata, begins with its burial in sediment and ends with the preservation of its hard parts in sedimentary rock.

Illustration by François Miville-Deschênes
2001
© Miguasha National Park


At the end of the 18th century, the quest for the age of the Earth propelled the nascent science of geology into a period of rapid development. But the first geologists, mostly European, clashed with religious dogmas, particularly those of Christianity. According to Scripture, the Earth had been created in only six days and had existed for at most a few thousand years...

By observing the slow accumulation of sediments in bodies of water and the time needed to compact them into rock, geologists of the day realized that our planet, with its great thicknesses of sedimentary rocks, must be millions, if not billions of years old. These estimates represent such considerable time spans that the human brain has difficulty comprehending them.


Once upon a billion...

seconds: The first personal computers appeared (1975), signifying the birth of Apple and Microsoft and the beginning of the Information Age. minutes: John completed his gospel. hours: Neanderthals buried their dead in the Near East. days: In Africa, Homo habilis began to fabricate better tools than Read More
At the end of the 18th century, the quest for the age of the Earth propelled the nascent science of geology into a period of rapid development. But the first geologists, mostly European, clashed with religious dogmas, particularly those of Christianity. According to Scripture, the Earth had been created in only six days and had existed for at most a few thousand years...

By observing the slow accumulation of sediments in bodies of water and the time needed to compact them into rock, geologists of the day realized that our planet, with its great thicknesses of sedimentary rocks, must be millions, if not billions of years old. These estimates represent such considerable time spans that the human brain has difficulty comprehending them.


Once upon a billion...

  • seconds: The first personal computers appeared (1975), signifying the birth of Apple and Microsoft and the beginning of the Information Age.
  • minutes: John completed his gospel.
  • hours: Neanderthals buried their dead in the Near East.
  • days: In Africa, Homo habilis began to fabricate better tools than those of Australopithecus.
  • months: The last of the great dinosaurs reigned on Earth.
  • years: Life consisted of bacteria, primitive multicellular plants and algae.


The age of the Earth is estimated at 4.57 billion years.


Unable to determine the exact ages of rocks and the Earth, British geologists began to classify the different sedimentary layers according to their relative ages. In doing this, they pioneered stratigraphy, a discipline that studies the succession of geologic layers. Stratigraphy is based on a number of principles, of which two are essential: a layer has the same age over its entire spread (the principle of continuity), and in the absence of structural overturning, a layer is always younger than the layers beneath it and older than the layers above it (the principle of superposition).
The study of a cliff, for example, allows one to see older sedimentary layers at its base and more recent layers at its summit.

Geologists soon noticed that fossil assemblages were not the same from one stratigraphic layer to another, and thus concluded that they must change over time. For example, the mountainous Jura Massif in Europe contains fossils that correspond to the time during which the encasing sediments were deposited. Wherever we find similar fossils elsewhere, we may suppose that they are the same age and we classify them as Jurassic. Groups of fossils at various stratigraphic levels represent different time periods. By crosschecking between different fossiliferous sites, geologists were able to put these assemblages in relative order and give names to the various time periods. This process produced the geologic timescale, a chronological representation of the Earth’s history, and biostratigraphy, a method of relative dating using fossils contained in the rocks.

Dating became much more precise with the advent of radiometric dating methods in the 1950s. Radiometric dating is based on the “lifespan” of radioactive elements in rocks, and this new approach allowed geologists to pinpoint the age limits between different periods. We know, for example, that the Jurassic began about 200 Ma ago and ended 55 Ma later. Radiometric dating is an “absolute dating” method, meaning that it gives an age in years instead of the “relative dating” offered by fossils, which only indicates only whether a rock is of the same age, older or younger than another rock.

© Miguasha National Park 2007

Tables of geological times

Major subdivisions of geological times. Ages in millions of years (Ma) were accredited by the International Commission on Stratigraphy (ICS) in 2004.

François Bienvenue
2007
© Miguasha National Park


Video

The stages in fossilization

An Eusthenopteron dies and sinks to the bottom of the ancient Miguasha estuary. He is then covered in layers of sediment that are compressed and hardened over time. Under the effect of erosion the now fossilized fish may reappear at the surface.

These are the stages in fossilization.

Miguasha National Park

© Miguasha National Park


During the first decades of the 19th century, geologists enthusiastically surveyed the British Isles and continental Europe in the hope of discovering fossils and assigning relative ages to the sedimentary layers that contained them. Gradually, the names of famous divisions in the geologic timescale began to emerge – like the Cambrian, Silurian, Carboniferous, Jurassic and Cretaceous periods – and these were named after historical or contemporary regions where the rocks of that period are plentiful (Cambria and Jura, for example), or where the rocks reflect the dominant characteristics of the time (“Age of Coal”, “Age of Chalk”, etc.). The geological timescale was finally, albeit slowly, taking shape.

The famous Scottish writer Hugh Miller (1802-1856), who popularized geology, was particularly interested in a sedimentary formation found in Wales, Scotland and Northern Ireland. Known as the Old Red Sandstone, this formation contains numerous fossils of ancient fish. Around 1830, it was thought that these sedimentary layers dated back to the beginning of the Carboniferous Period. For Hugh Miller, a creationist who nonetheless accepted t Read More
During the first decades of the 19th century, geologists enthusiastically surveyed the British Isles and continental Europe in the hope of discovering fossils and assigning relative ages to the sedimentary layers that contained them. Gradually, the names of famous divisions in the geologic timescale began to emerge – like the Cambrian, Silurian, Carboniferous, Jurassic and Cretaceous periods – and these were named after historical or contemporary regions where the rocks of that period are plentiful (Cambria and Jura, for example), or where the rocks reflect the dominant characteristics of the time (“Age of Coal”, “Age of Chalk”, etc.). The geological timescale was finally, albeit slowly, taking shape.

The famous Scottish writer Hugh Miller (1802-1856), who popularized geology, was particularly interested in a sedimentary formation found in Wales, Scotland and Northern Ireland. Known as the Old Red Sandstone, this formation contains numerous fossils of ancient fish. Around 1830, it was thought that these sedimentary layers dated back to the beginning of the Carboniferous Period. For Hugh Miller, a creationist who nonetheless accepted that our planet and the life it supported had long histories, these fossils represented the first fishes ever created.

At that time, all animals of the Carboniferous were considered to be descendents of Silurian fauna. But geologists studying marine fossils in southern Devonshire County could not agree on their ages. After several years of research and comparisons with various sites in Europe and elsewhere, the evidence was clear that a new stratigraphic system must be inserted between the Silurian and Carboniferous. Thus, in 1839, Devonshire inspired Adam Sedgwick and Roderick Murchison to name this new period the Devonian.

It was still not understood that the Old Red Sandstone was the terrestrial equivalent of the Devonian marine layers in southwestern England, and it took many more studies and discussions before the equivalence of these Devonian layers could be established. Strangely, the decisive argument that ended the controversy was the discovery by Louis Agassiz of a fish scale in a marine limestone under a Carboniferous layer in Belgium that was identical to scales from the fish Holoptychius, already discovered in the Old Red Sandstone in Scotland (and later at Miguasha). Some fossiliferous Devonian layers in North America bear a remarkable resemblance to the continental Old Red Sandstone, such as the Catskill Formation in western Pennsylvania, and the Escuminac Formation at Miguasha.

© Miguasha National Park 2007

The Devonian

Subdivisions of the Devonian System. Ages in millions of years (Ma) were accredited by the International Commission on Stratigraphy (ICS) in 2004.

François Bienvenue
2007
© 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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