On Friday I went on the CLA tour of the new Johnson Geo Centre in St. John’s. I enjoyed it so much I returned on Sunday to brush up on my geological terms and to chat with the tour guides, one of whom was working on a PhD on Precambrian fossils. The Geo Centre also has exhibits on the Titanic and the petroleum industry (the latter being counterbalanced by some global warming exhibits and regular showings of Al Gore’s An Inconvenient Truth).
Newfoundland rocks are old– too old for dinosaurs fossils but not for fossils of some of the most ancient multicellular life ever found. These are soft-bodied Precambrian animals that are very difficult to find because soft-bodied creatures do not fossilize well. These lifeforms lived in the sea 575 to 560 million years ago. The significance of these fossils is that they fill a void between the long reign of single-celled life and the “Cambrian explosion” when small sea creatures appeared relatively suddenly, many with bizarres shapes with no descendants living today. The soft-bodied Precambrians were like a mixture of animal, plant, and fungus, living deep in the ocean, often tethered to the bottom, absorbing organic material like animals, but appearing like ferns (one frond discovered is two metres long). Amazingly their large size was due to a growth process that is fractal-based. Each frond is made up of identical but smaller fronds, and so on all the way down to the smalled scale visible.
An incredible sequence of events in Earth’s history may explain the appearance of the Precambrians. Only five million years before their appearance the Earth was nearly frozen over in a period called the Gaskiers glaciation (this period is also somtimes called “Snowball Earth”). The retreating glaciers would have freed up dissolved organic material creating a rich food source for any life that could exploit it. Studies have shown that there was a massive increase in deep sea oxygen at this time, and oxygen is a potent (although initially highly reactive and toxic) source of energy for life.
The fossilized remains of soft-bodied Precambrian life found on the Avalon Peninsula in Newfoundland.
The museum at The Rooms also has a good display of fossils. The fossilized fronds on the left are Precambrian and the fossils on the right are trilobites, a very successful creature that appeared during the Cambrian period but died out during the great Permian-Triassic extinction event 251 million years ago when 96 percent of all marine species and 70 percent of all terrestrial vertebrate species went extinct.
In addition to having very old fossils, Newfoundland consists of rocks that are amongst the oldest ever found on Earth. The accordion-like appearance of much of Newfoundland’s land mass is testimony to the shifting plates of land on the surface of the Earth. In fact, discoveries in Newfoundland led to the acceptance of the plate tectonic theory, which is the theory that there are several large land masses on Earth moving and colliding into each other. Parts of Newfoundland share characteristics with land masses in Africa and Europe. The collision of plates has even resulted in rocks normally found deep in the Earth to be pushed to the surface. The Tablelands region on the west coast of Newfoundland is largely lifeless because of peridotite which is rock from the roots of continents, and full of magnesium, toxic heavy metals, and iron that rusts when exposed to the surface.
I also learned quite a few geological terms, and I can now better appreciate the fascination that geologists have about a place whose history can be reconstructed by a study of the rocks. I now know the three rock groups quite well. Sedimentary rock is formed from the layering or precipitation from solution of weathered rocks (or biogenic material, which is the basis of coal). Examples of sedimentary rocks are shale, siltstone, sandstone, breccia (angular pebbles cemented together), and conglomerate (rounded pepples smoothed by running water which have been cemented together– the rocks of Signal Hill are mostly conglomerate sedimentary rocks).
Igneous rock is derived from the cooling of magma, which is melted rock below the surface. The magma that is cooled above the ground or in the water is called extrusive igneous rock. Cooled below the ground, the rocks are called intrusive igneous rocks. An example of an intrusive igneous rock is granite, which constitute the central core of mountains.
The third type of rock is metamorphic, which is the result of a transformation of a previous type of rock. For example, slate is metamorphic rock derived from sedimentary shale. Marble is derived from limestone. The oldest known intact piece of the Earth’s crust is in northern Canada, and this metamorphic gneiss rock has been dated to being about 4 billion years old. Some samples of these incredibly ancient gneiss rocks were on display at the Johnson Geo Centre.
The CLA group arrives for the tour at the Johnson Geo Centre.
I took this picture from Cabot Tower at the top of Signal Hill. The Johnson Geo Centre is visible beside the pond which is at about the half way point on the hike up Signal Hill from St. John’s Harbour.
Labradorite, the provincial mineral, formed in slowly cooling intrusive igneous rocks (magma which has cooled below the Earth’s surface). Labradorite stands out with its shifting iridescent colours of blue, green, grey and bronze.
The Johnson Geo Centre is also home to a Titanic exhibit as well as a petroleum exhibit which highlights Newfoundland’s offshore oil industry.
An inukshuk (or inuksuk) shows the pass through the mountains. Inukshuk means “something which acts for or does the function of a person.” In this exhibit, the inukshuk communicates direction and safety.