econintersect.com
       
  

FREE NEWSLETTER: Econintersect sends a nightly newsletter highlighting news events of the day, and providing a summary of new articles posted on the website. Econintersect will not sell or pass your email address to others per our privacy policy. You can cancel this subscription at any time by selecting the unsubscribing link in the footer of each email.



posted on 08 November 2015

Elementary New Theory On Mass Extinctions That Wiped Out Life

from The Conversation

-- this post authored by John Long, Flinders University and Ross Large, University of Tasmania

Throughout the past 600 million years there have been five major mass extinction events that devastated life on Earth. While some of these events are very well studied, such as the killer asteroid that wiped out the dinosaurs 66 million years ago, others are more enigmatic and entertain a variety of possible causes.

The first three extinction events took place near the end of the Ordovician Period (around 445 million years ago), end of the Devonian Period (from 385 to 359 million years ago) and at the end of the Permian Period (252 million years ago).

The most devastating of all these events was the end of the Permian period, which wiped out some 96% of all marine species and about 70% of all known species on Earth.

The likely causes are massive volcanic eruptions on a scale never before seen, with other effects that include runaway greenhouse effect triggered by methane release from clathrates on the seafloor. Because the devastation was so severe, recovery took around 10 million years.

The big extinction event at the end of the Ordovician is linked to glaciation and widespread anoxia, or loss of oxygen in the seas. About 57% of all marrine life was wiped out in the oceans, making it the second largest of all extinction events.

The reliability of interpreting the past oxygen levels of the Earth is key to understanding this event, as perhaps the anoxia was brought on by another cause.

Why trace elements matter

New research by our team published this week in Gondwana Research has shown that a depletion of trace elements in the oceans could be another major factor in this extinction and two other major extinction events.

In an earlier article we explained the natural cycle of nutrients caused by plate tectonics, as increased erosion of the Earth's crust supplies nutrients such as trace elements to the oceans.

Trace elements such as zinc, copper, cobalt, manganese and selenium, in particular, are required for life in doses that have a very specific tolerance range. Too much or too little selenium can be toxic.

Tolerance levels of selenium for phytoplankton, molluscs, fish and many land plants and animals are very well known. Recently, selenium deficiency in large parts of China and Africa has been linked to major outbreaks of diseases such as AIDS, SARS, Ebola and Avian flu (H1N1). This is because lack of selenium impacts on the immune systems.

Such dangerously low levels of certain trace elements, such as selenium, could be a new factor in three major mass extinction events. But how could this occur?

Selenium abundances in the oceans over the past 550 million years. Note severe depletion of this vital trace element at three major extinction events (red triangles), suggesting this was a possible factor in these extinctions. John Long & Ross Large

Could selenium depletion cause mass extinctions?

If the oceans rapidly dropped their levels of selenium by around two orders of magnitude, would food chains likely be effected? This is precisely what happened at or near the end of the Ordovician, Devonian and Triassic Periods.

We suggest that critically low levels of selenium in past oceans would have affected the survival of plankton, eventually leading to collapse of the food chains, and extinctions. Selenium has recently been found to play a vital role in photosynthesis in phytoplankton.

Glaciation and lack of oxygen in the oceans are common explanations for the death of some 60% of all marine invertebrate species. But our data shows a severe selenium depletion event happened before the onset of extinctions, allowing suitable time for the collapse of food chains.

The end of the Devonian period around 359 million years ago saw the extinction of major groups like the placoderm fishes. This period includes four biotic crises, including two major extinction events for which global anoxia in the oceans is often blamed.

Our new data indicate a prolonged period of selenium depletion occurred at least 10 million years before oxygen reached its lowest point. Some Australian researchers also show that lack of oxygen in late Devonian seas was restricted to local basins and not necessarily a global phenomenon.

Placoderm fishes, like this six metre long Dunkleosteus, were one of the major groups to go extinct at the end of the Devonian period. John Long

The extinction event at the end of the Triassic, about 201 million years ago, mostly affected life in the oceans, with some 34% of marine species declining including the extinction of conodonts, a major invertebrate group.

Some reptile groups also went extinct on land. It has been shown that selenium uptake in the oceans by plankton effects transmission of selenium by gases to the atmosphere, so oceanic depletion of selenium could in theory effect levels on land.

Another question is whether selenium, which seems to be a very good proxy for determining past oxygen levels, was the prime driver for the loss of oxygen in the oceans which caused the extinctions, or was itself the main cause of extinctions.

One issue with our preliminary study is the dating of our samples does not always match the precise timing of the extinction events. This is purely an artefact of the sampling. Additional samples dated closer to extinction times are currently being analysed for the follow up study.

The bright side of mass extinctions

The cycle of nutrients from the supply of essential trace elements that begin the food chains for all life in the oceans is driven by plate tectonics. The uplift of mountains at plate margins causes erosion of crustal surfaces enabling trace elements to wash into rivers and end up in the seas.

When erosion is prolonged and tectonics is slow, the supply of these nutrients slows down, and depletion of certain elements begins. Only activation of Earth's engine, to drive more mountain building, seems to set the cycle back to normal again.

Yet mass extinctions have their bright side. Without them new life couldn't emerge and take priority place. The early tetrapods survived the end of the Devonian extinction event, a time when many prominent vertebrate groups went extinct.

Without this line of vertebrates surviving, the reptiles and mammals would not have had a chance to evolve. Mammals rose to prominence after the decline of the dinosaurs, and thus we are here today, thanks mainly to these mass extinction events many millions of years ago.

The ConversationJohn Long, Strategic Professor in Palaeontology, Flinders University and Ross Large, Distinguished Professor of Geology, University of Tasmania

This article was originally published on The Conversation. Read the original article.

>>>>> Scroll down to view and make comments <<<<<<

Click here for Historical News Post Listing










Make a Comment

Econintersect wants your comments, data and opinion on the articles posted.  As the internet is a "war zone" of trolls, hackers and spammers - Econintersect must balance its defences against ease of commenting.  We have joined with Livefyre to manage our comment streams.

To comment, using Livefyre just click the "Sign In" button at the top-left corner of the comment box below. You can create a commenting account using your favorite social network such as Twitter, Facebook, Google+, LinkedIn or Open ID - or open a Livefyre account using your email address.



You can also comment using Facebook directly using he comment block below.





Econintersect Contributors


search_box

Print this page or create a PDF file of this page
Print Friendly and PDF


The growing use of ad blocking software is creating a shortfall in covering our fixed expenses. Please consider a donation to Econintersect to allow continuing output of quality and balanced financial and economic news and analysis.


Take a look at what is going on inside of Econintersect.com
Main Home
Analysis Blog
The Truth About Trade Agreements - and Why We Need Them
Big Mess in Italy
News Blog
Early Headlines: Asia Stocks Up, Oil Down, House Has Stopgap $ Bill, Trump Sold All Stock, Euro Holding On, May Doubles Down, India Economy Struggles, Oz GDP Contraction And More
President Trump Must Be One-Term, Voluntarily!
Documentary Of The Week: Untold History Of The United States, 1890s To 1920
Where MPs Stood On Brexit
How Accurate Are Final US Election Polls
Brexit In The Supreme Court - Here's What It All Means
The States Where It's Legal To Smoke Marijuana
What We Read Today 06 December 2016
This Truck's Barrier Expands Out Of The Back For A Quarter Mile
October 2016 Manufacturing New Orders Improved
3Q2016 (Final): Headline Productivity Improves
October 2016 Trade Data Mixed
October 2016 CoreLogic Home Prices Year-over-Year Growth Rate Now Improved to 6.7%.
Investing Blog
Exuberance Returns
Investing.com Technical Summary 07 December 2016
Opinion Blog
Trump And Modi: Birds Of The Same Feather, But With Different World Views
Oil Deal Won't Last Long
Precious Metals Blog
Silver Prices Rebounded Today: Where They Are Headed
Live Markets
06Dec2016 Market Close: Wall Street Closed Higher, Commodities Remain Weak, The Bull Marches On
Amazon Books & More






.... and keep up with economic news using our dynamic economic newspapers with the largest international coverage on the internet
Asia / Pacific
Europe
Middle East / Africa
Americas
USA Government



Crowdfunding ....






























 navigate econintersect.com

Blogs

Analysis Blog
News Blog
Investing Blog
Opinion Blog
Precious Metals Blog
Markets Blog
Video of the Day
Weather

Newspapers

Asia / Pacific
Europe
Middle East / Africa
Americas
USA Government
     

RSS Feeds / Social Media

Combined Econintersect Feed
Google+
Facebook
Twitter
Digg

Free Newsletter

Marketplace - Books & More

Economic Forecast

Content Contribution

Contact

About

  Top Economics Site

Investing.com Contributor TalkMarkets Contributor Finance Blogs Free PageRank Checker Active Search Results Google+

This Web Page by Steven Hansen ---- Copyright 2010 - 2016 Econintersect LLC - all rights reserved