What caused the mass extinction of Earth's first animals?

What caused the mass extinction of Earth's first animals?
Zhang examining a new drill core in Three Gorges area (Hubei Province), People's Republic of China. This drill core includes sedimentary rocks from the middle Ediacaran to the Early Cambrian. Credit: ASU

Fossil records tell us that the first macroscopic animals appeared on Earth about 575 million years ago. Twenty-four million years later, the diversity of animals began to mysteriously decline, leading to Earth's first know mass extinction event.

Scientists have argued for decades over what may have caused this mass extinction, during what is called the "Ediacaran-Cambrian transition." Some think that a steep decline in dissolved oxygen in the ocean was responsible. Others hypothesize that these early animals were progressively replaced by newly evolved animals.

The precise cause has remained elusive, in part because so little is known about the chemistry of Earth's oceans that long ago.

A research team, led by scientists from Arizona State University and funded by NASA and the National Science Foundation, is helping to unravel this mystery and understand why this extinction event happened, what it can tell us about our origins, and how the world as we know it came to be.

The study, published in Science Advances, was led by ASU School of Earth and Space Exploration graduate student Feifei Zhang, under the direction of faculty member Ariel Anbar and staff scientist Stephen Romaniello.

What caused the mass extinction of Earth's first animals?
Zhang sampling Ediacaran carbonate rocks in Three Gorges area, Hubei Province), People's Republic of China. Credit: ASU
The importance of oxygen

Today there is an abundance of oxygen, a vital component of life, throughout most of the Earth's oceans. But there is evidence to suggest that during the , there was a loss of dissolved oxygen in Earth's oceans, an effect called "marine anoxia."

To get a better understanding of the mass extinction event, the research team focused on studying this effect. They wanted to determine not only how much of the ocean was anoxic when the animals began to decline, but also whether marine anoxia contributed to the decline and eventual of the early animals.

Integrating geochemical data and the Earth's fossil records

To determine the levels of marine anoxia and its effects, the research team used a novel approach of combining geochemical data and the Earth's fossil record to precisely match evolutionary and environmental events.

Typically, scientists determine ocean anoxia levels by looking at the abundance of pyrite, commonly known as "fool's gold," and other elements and minerals in ancient mud rocks. But mud rocks only provide clues to what may have happened at a single location. Scientists need to sample dozens of sites around the world to infer the big picture from mud rocks.

What caused the mass extinction of Earth's first animals?
Terminal Ediacaran carbonate rocks in Three Gorges area (Hubei Province), People's Republic of China. These rocks were deposited in a shallow marine environment between 551 and 541 million years ago, and hold a record of the marine environmental changes that occurred at the time they were deposited. Credit: ASU

To overcome this, the team pioneered a new and more efficient approach. Rock samples of marine limestone were collected in the Three Gorges Area (Hubei Province) of the People's Republic of China. This area is known for having some of the best examples in the world from the Ediacaran Period. The rock samples for this study were deposited in a shallow marine environmental between 551 and 541 million years ago, and hold a record of the marine environmental changes that occurred when they were deposited.

Back at the lab, the team measured the uranium isotope variations in marine limestone and then then integrated the uranium isotope data and paleontological data from the same suite of rocks. Once the data were integrated, the team could clearly see that the episode of extensive marine anoxia coincided with the decline and the subsequent disappearance of early animals.

"This may have been most severe marine anoxic event in the last 550 million years," says Zhang. "Mathematical modeling of our data suggests that almost the entire seafloor was overlain by anoxic waters during the end of the Ediacaran Period."

Is there a mass extinction in our future?

While our oceans currently have an abundance of oxygen, there has been a recent measurable rise in ocean anoxia, attributed by scientists to climate change. Advances in the study of ancient marine anoxia, like this one, then may help us understand and predict what lies ahead.

"The past is our best laboratory to understand the future" says co-author Anbar "It's sobering to see how often the mass extinctions of the past were preceded by increases in anoxia. There is a lot we don't understand about climate change, but the things we do know are a big cause for concern."


Explore further

Studying oxygen, scientists discover clues to recovery from mass extinction

More information: Feifei Zhang et al, Extensive marine anoxia during the terminal Ediacaran Period, Science Advances (2018). DOI: 10.1126/sciadv.aan8983
Journal information: Science Advances

Citation: What caused the mass extinction of Earth's first animals? (2018, June 27) retrieved 18 June 2019 from https://phys.org/news/2018-06-mass-extinction-earth-animals.html
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Jun 27, 2018
There appears an ugly number, about [60 x (10^6)] that historically has marked the greatest global disasters. About 512 mya this above Terminal Endiacaran to Cambrian Transition....[that took out the graboids...grin] with its global anoxia...and later the Permian Triassic Transition about 256 mya which featured another global anoxia. The 256mya event maybe had a cosmic impact cause that generated the Siberian Traps at the contra-coup point to the antipodal asteroid strike. 128myz brought the unzipping of PanGaia into the Americas and Euro/Africa. That must have been a hum dinger but the smoking guns of the Endicardian, Permian, and that one so far elude the study groups. The most recent, 66 mya as in the Bibical '666' may= 66x[10^6] was the Chixculub event. All those events are all those multiples hanging over our heads NOW cuz they are just THAT many years ago.

Jun 28, 2018
That is spooky. But that last figure of 66mya doesn't add up to 128mya. It might be that the dating of the Chicxulub strike is wrong and should be 64mya? Someone miscalculated, perhaps?

Jun 28, 2018
Fossil records tell us that the first macroscopic animals appeared on Earth about 575 million years ago.


They keep using the word "appeared" as though all of a sudden, "here they are". But then they have to use that word because there is an overwhelming absence of evidence of intermediate steps from basic to complex life.

Jun 28, 2018
Macro life 'appeared' from micro life about 575 mya. A million or two years is enough wiggle room for evolution to go from specialized cells clumping together to clumping lengths of them into wormlike creatures.
In geologic terms, 'suddenly appeared' can mean millions of years, after all, Earth has been a globe for 4,500 million years. That is a lot of millions.
Those tiny intermediate lifeforms are slowly being teased out of the matrix.
Australia has the lead in transitional fossil traces.

Jun 28, 2018
If I understand you damn fools correctly? You are demanding that verifiable facts are to be censored? All required to repeat the crackpot stuporstitions of your monkey tribe's beliefs?

Are you guys? so lacking in self-awareness that you do not realize how ridiculous you seem?

Yeah! Back to the 5th Century in one bounding leap of mass stupidity.

After you legislate to require that Pi exactly equals 3.0. And that all evolutionary, genetic, geology, cosmology and agricultural sciences are outlawed in favor of your official approval of Lysenkoism and creationism.

Then I guess you will be pushing to reintroduce feudalism? Following up with mandating the divine right of kings.

What a pack of idiots! As I have said before. In your (unearned ) pride rejects reality. Submitting yourselves in worshipful obeisance to pharaoh.

Jun 29, 2018
If I understand you damn fools correctly? You are demanding that verifiable facts are to be censored? All required to repeat the crackpot stuporstitions of your monkey tribe's beliefs?

Are you guys? so lacking in self-awareness that you do not realize how ridiculous you seem?

Yeah! Back to the 5th Century in one bounding leap of mass stupidity.

Then I guess you will be pushing to reintroduce feudalism? Following up with mandating the divine right of kings.

What a pack of idiots! As I have said before. In your (unearned ) pride rejects reality. Submitting yourselves in worshipful obeisance to pharaoh.


says rrwillsj

Welllll, I guess you gave 'em what for. How DARE THEY?

Maybe they will all come to their senses and realise that what you have been saying, is gospel truth.

Jun 29, 2018
Evilution stories always bring out the Babble-thumpers.

Jun 29, 2018
S_E_U the deity talks to me, does the creature talk to you? The deity seems to enjoy pestering me for being a materialist atheist. I have fun joking about the godling as a 13+billion year old infant. Still just a baby! We seem to amuse one another.

And no I'm not going to obey the infantile obsessions of the little critter. Maybe in a few hundred billion years when it has matured? Maybe then it will have something to say worth listening to?

The way to tell that it is not an angel of one varieety or another is talking to you? Apply the Turing Test. As those are just robots. For which I have even less enthusiasm about listening to. Machine /Artificial Intelligence is just a bad joke out of comicbooks.


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