Plants That Want to Kill Us

By Dr. Graham Young, past Curator of Palaeontology & Geology

Recently, there seem to have been a lot of stories in the media about the remarkable intelligence of elephants. Scarcely a week goes by without a new science story about how elephants are among the few non-human creatures that are self-aware, about their superb communication skills, about the ways in which they care for one another, or about their wonderful memories (it is true: an elephant never forgets). Whenever I see these stories I feel wistful, contemplating the elephants that used to live around here. I imagine how they wandered across the landscape, using their big brains as they communicated about food and predators.

If you are here in still-snowy Winnipeg, you might wonder if I am feeling OK, or you would at least think “what does this have to do with our local situation?” After all, wild elephants live a very long way away, in warm parts of Africa and Asia. Our lack of living elephants is, however, a disparity of time rather than one of geography. Geologically speaking, it is just the blink of an eye since the time when this area was regularly visited by herds of elephants.

I am speaking, of course, about mammoths. Although woolly mammoths (Mammuthus primigenius) are better-known from Ice Age (Pleistocene) deposits in Siberia, Alaska, and the Yukon, many examples have been found across the Canadian Prairies. Quite a few mammoth bones and teeth have been collected in Manitoba, along with the occasional tooth belonging to their distant cousin the American mastodon (Mammut americanum).

Some of our mammoth bones are from sites where associated wood material has been dated to about 40,000 years old, so they date from well before the end of the Ice Age. The last mammoths in North America, however, became extinct about 10,000 years ago, and the very last ones in the world lived on Wrangel Island, Siberia, until just 4,000 years ago (by which time the Egyptians had already constructed some of their pyramids!). We don’t really know why mammoths became extinct, but there seem to have been several factors involved: climate change at the end of the Ice Age and increased hunting by human populations may have been the major causes.

Many of the new things we are learning about elephant behaviour seem to apply to both Asian and African elephants. Given what we now know about evolutionary relationships, it must be assumed that mammoths would have had the same sort of intelligence and behavioural traits, and it is possible that even mastodons were somewhat similar. The new information on elephant intelligence is allowing mammoths to be well understood as “living” creatures, even if the attempts to clone them are unsuccessful.

It is saddening that we came so very close, geologically, to seeing those herds of mammoths. Whenever I look at those fossils, whenever I contemplate the tusk of a huge adult or the jaw of a baby mammoth, I miss the animals.

By Dr. Graham Young, past Curator of Palaeontology & Geology

A couple of weeks ago, I gave a presentation at McNally Robinson in Winnipeg, as part of our Museum lecture course Into the Vault. I was planning to talk about the ancient island shoreline deposits we have been studying in the Churchill area, and as I thought about history and pre-history, I was reminded of an observation I had made during an earlier trip to southwestern Manitoba. In most parts of a relatively flat landscape, the ground surface is the result of processes in the present day and the recent past; it is only where some of that surface is peeled away that we can really see evidence of a deeper past.

Where the earth is split open, along riverbanks and shorelines, and at roadcuts and quarries, we can see its older layers. While the surface usually represents the present, recent past, and relatively recent prehistory, the layers below that surface may be extremely old. Southwestern Manitoba and the Hudson Bay Lowland are both in the part of North America known geologically as the Platform, which has been free for a very long time from disruptive forces such as earthquakes and volcanoes. As a result, the layers are relatively orderly; the sediment was laid down almost horizontally, layer upon layer. Slicing through them vertically looks quite similar to slicing an onion with a knife.*

As we dig down into the upper surface of the land, below the historic remnants we can see evidence of prehistoric occupation of this region. Almost everyone is familiar with widespread artifacts such as arrowheads, but in some places in southern Manitoba we can see ancient burial mounds or traces of long-past hunting sites.

Elsewhere, the cuts in the Earth extend into older layers. Some of these layers are still made of sediment that has not been turned to rock, but they date from the late part of the Ice Age, before people are known to have lived in this part of the world.

The geological time gaps in the Manitoba record (such as between the Mississippian and Jurassic rocks, where we might have expected deposits from the Pennsylvanian, Permian, and Triassic periods) simply represent intervals in which sediment was not being deposited in this region, and was perhaps being eroded.  Most of our sedimentary rocks were deposited under seawater; the intervals of deposition occurred at times when the sea invaded the middle of the continent, and the gaps in deposition represent times when the sea left this region. We are in the latter sort of situation nowadays, though of course sediment IS still being deposited in one part of the middle of North America: in Hudson Bay.

The layers in the diagram below look to be strongly tilted, but this is because the diagram has a 200x exaggeration of the vertical scale, relative to the horizontal. In reality, they are tilted just a few degrees. The tilt is related to their having been deposited on a seafloor that sloped gently toward the centre of the ancient sedimentary basin, which was located to the southwest.

This slight tilt is, however, very important when we consider where we might find particular layers on the surface. Geologists often talk about the rocks of the Platform as having “layer cake stratigraphy.” Like the onion, the layer cake is a useful metaphor. If we imagine a cake plate being tilted, and then the cake being cut parallel to the tabletop, it is obvious that the lower layers of the cake would be visible from above as you move away from the direction of tilting.

The Shield rocks are geologically complex, having been formed as mountains were growing, volcanoes erupting, and continents crashing together in this region about 1.8-3.5 billion years ago. Since they were formed by such active processes, they are often folded, faulted, and overturned; as a result we can no longer apply our simple onion/cake metaphors once we reach those rocks. But those comparisons work wonderfully in any of Manitoba’s younger strata!

* The growth of onions is apparently quite different from this age-layering of sediment on the Platform, but it is still a handy visual metaphor.