Solving the Puzzle of Late Devonian Mass Extinctions
The huge Bakken Shale Formation, which covers an area of 200,000 square miles under Canada and North Dakota, has been producing oil and gas for our continent since the last 70 years. Recently some new discoveries were made which could help us get a better understanding of the geological history of Earth.
A group of scientists from the University of Maryland, George Mason University and Equinor (an oil and gas company from Norway) have found a new way to look at the fossils and chemicals in rocks.
Recently researchers discovered something amazing about Earth almost 350 million years ago. They found out that a major cause of many biotic crises in the late Devonian Period was euxinia – when oxygen runs out and hydrogen sulfide increases in big bodies of water. This connection between sea levels, climate, ocean chemistry, and biotic disruption was published in the journal Nature.
UMD Geology Professor Alan Jay Kaufman and his team have figured out how massive species losses regularly took place during the late Devonian Period. This is something that scientists had never seen before. According to Prof. Kaufman, these extinctions were likely caused by an expansion of hydrogen sulfide, but there hadn’t been tests run into this idea until now.
Kaufman said that the late Devonian Period was very important in shaping the Earth into what we know it as today. Plants and trees growing on land were particularly influential because they held soil together, transported nutrients for sea creatures to eat, and changed the atmosphere by adding oxygen, water vapor and removal of carbon dioxide.
“The introduction of plants that were able to use light energy to make food and give off water started the Earth’s cycle that allowed for more complex living creatures like we know them today,” Kaufman said.
The Devonian Period stopped around the same time Bakken sediments were piling up, so these layers of shale that were high in organic material could “memorize” the environment back then. All the continents on Earth had flooded, and different kinds of sediment – including black shale – gathered in kinds of inland seas like the Williston Basin which helps to preserve the Bakken formation still today.
Tytrice Faison, a student at the college, joined a professor’s lab after taking his class. Tytrice studied over one hundred rocks and particles of shale and carbonate. After analyzing these samples, the professor and Tytrice figured out that there were three big times when loads of creatures died – known as Annulata, Dasberg and Hangenberg events. The last event was one of the worst mass animal/creature deaths in history!
Kaufman said that we could find certain events in history, shown by black shale and other chemical remains. We think these events might be from when sea levels got higher because of melting ice near the South Pole.
If sea levels had been higher, the area on land between the ocean and the continent (called interior continental margins) would have gotten flooded. This flooding would have caused a lot of nutrients like phosphorous and nitrogen to mix into big bodies of water, which then made algae grow quickly in huge amounts. Too much algae would suck all out oxygen from the water and make it poisonous, killing animals in the oceans and on shorelines around that area. That’s what might’ve happened during some events in late Devonian times.
The team’s research isn’t about something that happened a long time ago – but things happening in our oceans today due to global warming. Kaufman compares the ocean’s circulation to a “conveyor belt” carrying nutrients, oxygen, and microorganisms from one place to another.
A special type of cold, salty water forms in the North Atlantic region. Then, it sinks to the bottom and is transported to different parts of the oceans like the Indian and Pacific Oceans. This helps spread oxygen throughout the ocean so living creatures can survive. If global warming causes this process to slow down, some areas of the ocean may lose oxygen and become too unhealthy for certain species.
Global warming may cause migration of animals away from dangerous places and result in less variety of species and increased number of extinctions.
Our research explains different things about Earth’s changes during a time when it changed from something totally unfamiliar to what we know today. It also shows us that there was a kind of “killing” happening back then, which likely caused numerous extinction events throughout our planet’s history. Additionally, this event is the source of most of the oil and gas found in the United States.
This study was sponsored by the company called Equinor, and it was published in the journal Nature on 8th March 2023. Its title is “Basin-scale reconstruction of euxinia and Late Devonian mass extinctions”.
