From Seas to Sands:

On its surface, Morocco’s landscape couldn’t be more distinct from that of Manitoba: towering snow-capped mountains, vast desert regions of exposed rock, and precious few lakes. And yet, when one peers deeper, these two regions have profound linkages in terms of their geological history. Both Manitoba and Morocco were once located close to the equator and largely submerged beneath vast seas during the early to middle Paleozoic Era, roughly 540 to 300 million years ago. The inundation of these distant continents was notably due to higher sea levels, thanks to less polar ice and tectonic processes occurring at that time. Owing to their similar past environments, there are also many connections in the fossils which can be found in these regions.

The destination for our field trip was a broad region of the Anti-Atlas Mountains along the edge of the Sahara Desert. Reaching them meant crossing over the High Atlas Mountains, a journey which took the better part of a day. Along the way, we passed villages nestled into the high peaks, majestic kasbahs (the Moroccan equivalent of castles), and roadside tourist stands showcasing a bewildering array of clothing, souvenirs, minerals, and fossils (many of them forgeries or highly altered). The rain shadow produced by the Atlas Mountains is straight out of a textbook; it was close to zero degrees, overcast, and snowing as we traversed the mountain pass, but transitioned to bright sun and up to 30 degrees as we descended into the desert beyond. Upon glimpsing the desert landscape, it’s no mystery why Morocco has been a filming site for many iconic movies and shows. As we broke for the night, we snacked on dates, biscuits, and tea served on polished stone tabletops sporting gorgeous fossil cephalopods.

Over time, oxygen built up in the atmosphere and oceans, leading to wide ranging effects such as the generation of the ozone layer that protects us from UV radiation, the oxidation of iron, producing most of the iron ore that we rely on today, the formation of thousands of new kinds of minerals which contain oxygen, and ultimately the evolution of more complex living cell types and the earliest multicellular organisms, which rely on oxygen for their metabolism. Ironically, the evolution of the first herbivorous animals seems to have led to a rapid decline in stromatolites around the beginning of the Cambrian Period. While less abundant, stromatolites still survive to this day in environments that are inhospitable for their herbivores, such as the famous Shark Bay site in Australia. Fossils of some of these post-Cambrian survivors also occur widely in Manitoba.

After driving for a few hours, we had an opportunity to visit the Fezouata Shale, which dates to the early Ordovician Period, around 477 million years ago. This site is world renowned for its fossilization of soft tissues and has been compared to other famous localities like the Burgess Shale. It also shares this type of preservation with three slightly younger sites in Manitoba: Cat Head, William Lake, and Airport Cove. This exceptionally preserved fossil deposit was first explored and recognized by Moroccan fossil collector Mohamed Oussaid Ben Moula. Ben Moula’s contributions to science have since been widely acknowledged, including through the naming of a species after him. We had the opportunity to visit Ben Moula’s family home and view some of his most recent collections, laid out in his yard! The fossils included beautiful trilobites preserving their antennae, giant marine filter feeders called radiodonts, armoured bristle worms, branching colonies of graptolites, and bizarre extinct echinoderms called stylophorans, to name just a few. Some of the fossils even represented new species (at least one that I spotted was acquired for a local museum collection). It will be exciting to see if any of the species found at Fezouata can also be found at sites in Manitoba. After the collection visit, we drove off the highway into the desert to one of the dig sites and were able to spend a short time searching for fossils. The group found some very nice trilobites and echinoderms, though none of the rarer species made an appearance.

After spending the night near Erfoud, we ventured forward in time to the Devonian Period, viewing a variety of sites ranging from about 400 to 360 million years old. The Devonian has been referred to as the “age of fishes,” and given the topic of our conference, our main goal was to survey the occurrence of these animals in the region. Two groups of fishes are particularly abundant in the region: early sharks and placoderms. The latter are thought to have been the first vertebrates to evolve jaws and teeth and include giant species like Dunkleosteus terrelli (a replica of which is on display in our Earth History Gallery) as well as more modest-sized Elmosteus lundarensis from Manitoba.

Our first Devonian site, Hamar Laghdad, preserves spectacular mud mounds – gigantic reef-like structures – teeming with fossilized life. As we ascended the peak from where our cars parked, we stepped over thousands of fossilized corals, brachiopods, cephalopods, and trilobite parts. In certain places, ancient crevices within the mud mounds were occupied by huge numbers of trilobites, possibly as safe havens for moulting their hard exoskeletons. Elsewhere, a quirk of fossil preservation caused by the movement of iron rich fluids through the rock has tinted the trilobites red and their eyes faintly green. Huge pits and caverns excavated by commercial collectors pointed the way to the richest fossil beds, and many fragments could be seen in the discard piles nearby. Slightly further along, in the youngest part of the outcrop section, we finally found fish remains. While stopping to chat with a colleague, I noticed a cylindrical chunk of fossil bone lying next to my boot. This turned out to be a section of the lower jaw of a placoderm fish called Alienacanthus malkowskii. This remarkable species had one of the most extreme “underbites” known from any animal! Shortly after, another member of our group found a large piece of bone belonging to Titanichthys termieri, a giant filter feeding placoderm. As we prepared to depart the site, we noticed several rock fragments on the desert floor near the cars which resembled stone tools, hinting at the long history of human occupation of this region.

The following day we were guided to two Devonian sites by local expert Moha Mezane. Mezane was first fascinated by fossils close to his home as a young boy and his keen eye for significant finds led to a number of important research contributions. His house also boasts an impressive display of fossils of all ages, ranging from trilobites and fish to ancient whale teeth and fossil trackways. Mezane led us into the desert near his house to a small outcrop featuring incredible trace fossils including trilobite trackways, fish swimming traces, and various invertebrate burrows. Further out, near El Atrous, we saw limestone beds tilted upright at an impressive angle. Scaling the piles of sand up to the exposed rock surfaces was a challenge, but well worth the effort. At the top we were greeted by partial skeletons of Alienacanthus and the shark Maghriboselache mohamezanei (named after Mezane). Such remains of sharks are particularly rare, since excepting their teeth, their skeletons are composed primarily of cartilage which is less resistant to decay than bone. The fossils were well-weathered by the desert wind and sand – it took a keen eye to spot them – but they still had many recognizable anatomical details. After wrapping up here, we finished the day with a very long, bumpy, off-road drive to our next hotel. We spent the night at Auberge Camping Oasis El Mharech, which is located in the heart of the dessert – it’s so remote its address is provided as GPS coordinates!

Waking early again, we journeyed on into the mountainous region between Tafraoute and El Maharch. Our next stop involved another steep climb to observe a variety of different geological layers, each with its own assortment of fossils. The bottom of the section, around 370 million years old, featured the “thylacocephalan layer,” which is named after the distinctive, extinct, big-eyed crustacean fossils that commonly occur there. The fossils were preserved inside concretions made of reddish ironstone and can be found by splitting open the concretions with a hammer. In addition to the thylacocephalans, rare fossil fishes can be found. One member of our group found an intact fin from a shark. Further up the slope, we crossed into different rock layers containing abundant cephalopods, brachiopods, and pieces of the bony armour of Dunkleosteus.  The top of the section featured a distinctive black shale consisting of sediment laid down 359 million years ago during a major extinction pulse (the Hangenberg event), characterized by widespread depletion of oxygen in the oceans, which wiped out placoderm fish and a range of other groups of organisms at the tail end of the Devonian Period. Pondering this dramatic shift in environment which fundamentally reshaped life on Earth seemed a fitting way to conclude our desert explorations.

After another long ride back to the road, we had the opportunity to see the personal collection of another significant local collector, Saïd Oukherbouch from Tafraoute, showcasing many intact shark and placoderm fossils found in this area. After taking in the sights here, it was time to begin our long journey back across the Atlas Mountains towards home.

Geologic time is truly staggering. It is hard to comprehend even for geologists, so we often rely on analogies to convey the vastness of time. If you could count one year per second, it would take an hour and 17 minutes until you had counted the age of the oldest Egyptian pyramids. Keep going, and it would take over 2 years before you reached the end of the age of dinosaurs. You would have to keep going for another 5 and a half years to get to the age of the earliest dinosaurs and another 12 on top of that to reach the earliest animals. It would be impossible to count to the age of the Earth, as it would take 144 years to get to 4.54 billion.

But, how do we actually know how old a particular specimen or event is? This is one of the most common questions I am asked as Curator of Palaeontology and Geology. It’s an excellent question, but not an easy one to answer in a concise way, so I will do my best to provide a more comprehensive answer here.

Manitoba has changed immensely over Earth’s history. While Churchill is now a cold, arctic environment close to 60 degrees north of the equator, about 450 million years ago it was equatorial and covered by a tropical sea. This is due to the shifting of the plates that make up the Earth’s crust, which move at about the speed that your fingernails grow.

You may have heard of carbon dating before. This approach relies on the radioactive decay of a naturally occurring form of the chemical element carbon. As with all elements, carbon atoms can come in several different forms, called isotopes. Isotopes share the same number of positive particles (protons) in their atomic nucleus, but differ in the number of neutral particles (neutrons). The majority of carbon on Earth is an isotope called carbon-12, which is stable. However, other forms of carbon exist, including an unstable form called carbon-14, characterized by two extra neutrons in its nucleus. Carbon-14 atoms decay over time, as one of their neutrons converts into a proton, releasing radiation and transforming the unstable carbon atom into a stable nitrogen atom. New carbon-14 is constantly being generated in the atmosphere by the action of cosmic rays from space which cause the conversion of nitrogen atoms into carbon-14.

Critically, the decay of carbon-14 happens at a predictable rate. By measuring this rate, we can predict that half of the carbon-14 that exists now will have decayed in 5,730 plus or minus 40 years. This length of time is known as the half life of carbon-14 and it is this concept that allows us to date materials made of carbon. Living organisms take in carbon, including carbon-14, either from carbon dioxide gas via photosynthesis or from feeding on other organisms. While organisms are alive, their supply of carbon-14 is continuously replenished. Once they die, carbon intake ceases and the carbon-14 “clock” is started. By measuring the amount of carbon-14 remaining in a sample of an ancient organism, we can calculate how long ago it died.

One of the oldest rocks on the surface of the Earth, called Acasta Gneiss, on display in the Earth History gallery. It is close to 4 billion years old and is found in Northwest Territories. The age of the Earth and Solar System are estimated to be even older based on measuring the age of meteorites and samples from the moon, which are less subject to processes that reset the radiometric “clock”.

Unfortunately, there’s a catch: if a sample is more than about 50,000 years old, the amount of carbon-14 remaining will be too small to permit an accurate age estimate. For older samples, scientists have to rely on different elements. For example, uranium-238 decays into lead-206 with a half life of about 4.47 billion years. Since uranium-238 is commonly trapped in in certain minerals when they form, it is ideal for measuring the age of older events in Earth’s history. Several other clocks, or more technically radiometric dating systems, exist and these can often be compared to each other to improve the accuracy of estimates.

Not every sample can be dated using an absolute method. For example, many fossils are too old for carbon dating and have insufficient uranium content for uranium-lead dating (although new approaches are pushing the boundaries of what is possible).

Similarly, sedimentary rocks like sandstones and limestones are formed of many different components including fragments of older rocks, fossils, and mineral crystals that have grown in between. Dating these components can give differing ages, sometimes producing misleading age estimates for samples. Further, alteration of rock under high heat and pressure or by the seeping of groundwater can enable atoms to move into and out of its crystalline structure (element mobility), which can “reset” the radiometric system.

This is where a second, complimentary approach called relative dating comes in. Even before there was a well-developed conception of evolution, scientists noticed that there was a regular pattern to the occurrence of different species throughout Earth’s rock record. We now know that this pattern is a consequence of the evolution and extinction of species. Mammoths, dinosaurs, and trilobites are all found only in particular rock layers and are absent from others. At a finer scale, careful examination reveals multiple successions of particular species, from which a comprehensive sequence can be built up. Since rock layers are deposited one on top of the other, the ordered succession of organisms gives us a clue about the relative age of the layers they are found in. If we can date rock layers above and below a particular fossil using radiometric dating, then we know that the fossil must be intermediate between those ages. If we then find the same fossil elsewhere, we have a relative idea of how old the rock it occurs in must be.

Fossils are not the only source of information that can be used for relative dating. Chemical and magnetic signatures also exhibit observable patterns of change through time that can be used to order rock layers by age. By combining insights from various relative and absolute dating methods around the world, the Earth’s timescale has been built up. The timescale is broken up into a number of named intervals, often based on particularly noticeable changes in the types of fossils. For example, the end of the Cretaceous Period is marked by the extinction of the dinosaurs, with the exception of birds.

Earth’s geological time scale should certainly be ranked among our most significant scientific achievements. This is the result of a long and fascinating history, with insights being drawn from multiple different disciplines of study around the globe. While we now have a pretty good idea of the age of key events throughout Earth’s history, new research is constantly refining dates, enabling us to understand events in the deep past with ever increasing precision.