|Ya Ta Hinda near where the Jurassic rocks were found.|
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However, immediately above this bed is a layer of rocks that shows that there was a sudden shift. Fossils are fewer and smaller. There was extinction of some animals. The culprit? The shift was caused by a decline of dissolved oxygen in the water which means that there was some mechanism in play to change the atmospheric chemistry. These events have occurred on occasion throughout the history of our planet. They are called anoxic events. Other anoxic events have also triggered extinctions.
What makes the discovery in Canada so interesting is that up until now, the only other evidence for a Jurassic anoxic event was found in Europe. Thus, the rocks in Canada show that the event was widespread and likely global in scale. Based on the research of anoxic events, it seems that they do not last long (geologically) and span about 1 million years. They likely occur as the earth "resets" from some unusual event.
Scientists have come up with many ideas as to what triggers these anoxic events. They include volcanic events, upwelling of hydrogen sulfide from the oceans, release of carbon dioxide into the atmosphere from the oceans, and addition of nutrients via weathering to oceans which causes algal blooms and associated eutrophication.
Regardless of the cause, the research provides a glimpse into ancient climate change and how it impacted ocean life.