This is the first in a series of four seasonal posts that speak to changes: environmental changes, cultural changes, generational changes, and seasonal changes. They’re all based on insights provided directly by life on the Farm and rooted in the tall grass prairie. We’ll call this series “Learning from the Land”.
There are two types of glacial sediments on Lone Tree Farm. Well-sorted sand and gravel was deposited by water from a melting glacier and poorly sorted clay with boulders deposited directly by the ice in an older glacier. This “outwash” sand and clay “till” have been described in several posts over this past year. The fractured till has served as an “aquifer” in the last several years when we had lots of rain. The flow conditions during high water levels in the Creek channel have eroded things from the buried outwash sands that provide clear lessons from the Land.
Ice Age fossils started showing up on modern sand bars! This tooth and bone are from a mammoth that lived in the general area about 10,000years ago. The fossils have been identified by a scientist who works at the Mammoth Site in Hot Springs, South Dakota. He’s seen a lot of mammoth remains and has lots of experience interpreting the environment that they lived in. The animals may not have lived directly in the glacial valley now occupied by the Kanaranzi Creek, but their remains probably washed down the meltwater stream to be deposited with the sand and gravel now located on the Farm.
That ancient stream came from the front of the melting glacier that was about 15 miles northeast of the Farm. This map is taken from a publication by the Minnesota Geological Survey and shows the valleys of the meltwater streams in yellow (4). The main ice mass of this last glacier in the area is marked by the light brown color (3) in the east and north half of the map. The end moraine that was the front of the glacier is the red-brown (3) strip that trends diagonally through the middle. And, the darker brown (4) western half of the map is deposits from an older glacier. Those are all geological interpretations based on the materials observed in the map area and on observations and interpretations from other areas. In addition to the mammoth fossils found on the Farm (A), there are collections from gravels to the northeast at Adrian, MN (B) and to the southwest at Rock Rapids, IA (C).
There is also a collection of mammoth remains from a location along the Big Sioux River near Brookings, SD, just to the northwest of the map area. That site also includes artifacts from the PaloIndians who were hunting these big beasts. Maybe there were also hunters working along Kanaranzi Creek back 10,000 years ago? There’s a theory that large Ice Age animals (called “megafauna”) like the mammoths, were hunted to extinction. But there’s still disagreement about this interpretation among the scientists who are doing these studies. There’s no disagreement about what mammoths look like, however. These two photos are reconstructions on display at the Mammoth Site in South Dakota.
And, there is pretty much complete agreement about the interpretations of the environmental changes that we know as the Ice Ages. The descriptions of earth materials and the age dates are universally accepted among the scientists who are trying to visualize the advance and retreat of the multiple glaciers. That doesn’t necessarily mean that everyone agrees about the causes of those environmental changes. One idea is that changes in the earth’s orbit helped produce the environmental shifts and there’s general consensus that carbon dioxide also played an important role.
This is all somewhat similar to the current debates around climate change and the COVID pandemic. There’s general agreement about the data (with some glaring exceptions), but there are dramatic differences in opinion about the interpreted causes. In fact, there’s a spooky similarity between the exponential growth curves for carbon dioxide levels in the atmosphere and the COVID case counts. And, these discussions are clearly mixed up/messed up with politics and opinions from people who are unfamiliar with the data. There are actually a couple of important lessons from the Land here: 1) adapt to new conditions or go extinct and 2) exponential growth is not sustainable in healthy natural systems.
The idea for this series of four holiday posts came from an invitation to contribute to a “Prairie Podcast” organized by the MN DNR for people working in the tall grass prairie. It’s not out yet, but I’ll let you know when it becomes available.
Interesting and educational. Nice pictures!
Very interesting thought that an orbital change could have contributed to the environmental change, but weren’t there multiple ice ages? Doesn’t seem the orbit could have bounced back and forth that many times —- wouldn’t it require multiple planetoid “near misses”.
I think orbital changes have been discussed, but I’m not sure about where the idea stands now. There is an additional astronomical cause proposed: procession of the earth’s axis. That’s been called on to explain some of the cyclical aspects, like the coal cyclic deposition. So that’s an additional glacial time (Pennsylvanian Period) and I think at least one more back even earlier (Precambrian). Bet that’s more than you want to know!