BIOTURBAZIONE

Una teoria dell'Università Danese attribuisce il merito della 

presenza stabile d'ossigeno nella nostra atmosfera - e quindi 

della vita come noi la conosciamo - all'attività nascosta di  

insospettabili piccoli organismi scavatori (anellidi, 

molluschi e simili invertebrati).

Il complesso meccanismo attraverso il quale ciò si è ottenuto 

- nell'arco di ere geologiche - si definisce 'bioturbazione' e 

non  è altro che la rielaborazione di sedimenti biologici da 

parte di animali particolari. 



Burrowing animals 

may have been key to stabilizing 

Earth's oxygen 


Ancient Environment, Breakingnews, Earth Science, Fossils, Palaeontology 2:30 PM Around 540 million years ago, the first burrowing animals evolved. When these worms began to mix up the ocean floor's sediments (a process known as bioturbation), their activity came to significantly influence the ocean's phosphorus cycle and as a result, the amount of oxygen in Earth's atmosphere. 

Fossil of burrow activity in sediment, 530 million years old 

 [Credit: Martin Brasier, University of Oxford]

 "Our research is an attempt to place the spread of animal life in the context of wider biogeochemical cycles, and we conclude that animal activity had a decreasing impact on the global oxygen reservoir and introduced a stabilizing effect on the connection between the oxygen and phosphorus cycles," says lead author Dr. Richard Boyle from the Nordic Center for Earth Evolution (NordCEE) at the University of Southern Denmark. 
The computer modelling study by Dr. Richard Boyle and colleagues from Denmark, Germany, China and the UK, published in Nature Geoscience, links data from the fossil record to well established connections between the phosphorus and oxygen cycles. 
Marine organic carbon burial is a source of oxygen to the atmosphere, and its rate is proportional to the amount of phosphate in the oceans. 
This means that (over geologic timescales) anything that decreases the size of the ocean phosphate reservoir also decreases oxygen. 
The study focuses on one such removal process, burial of phosphorus in the organic matter in ocean sediments. The authors hypothesize the following sequence of events: Around 540 million years ago, the evolution of the first burrowing animals significantly increased the extent to which oxygenated waters came into contact with ocean sediments. 
Exposure to oxygenated conditions caused the bacteria that inhabit such sediments to store phosphate in their cells (something that is observed in modern day experiments). This caused an increase in phosphorus burial in sediments that had been mixed up by burrowing animals. This in turn triggered decreases in marine phosphate concentrations, productivity, organic carbon burial and ultimately oxygen. Because an oxygen decrease was initiated by something requiring oxygen (i.e. the activity burrowing animals) a net negative feedback loop was created. 
Boyle states: "It has long been appreciated that organic phosphorus burial is greater from the kind of well oxygenated, well-mixed sediments that animals inhabit, than from poorly mixed, low oxygen "laminated" sediments. The key argument we make in this paper is that this difference is directly attributable to bioturbation. 
This means that 

(1) animals are directly involved in an oxygen-regulating cycle or feedback loop that has previously been overlooked, and 

(2) we can directly test the idea (despite the uncertainties associated with looking so far back in time) by looking for a decrease in ocean oxygenation in conjunction with the spread of bioturbation. 

My colleague, Dr Tais Dahl from University of Copenhagen, compiled data on ocean metals with oxygen-sensitive burial patterns, which does indeed suggest such an oxygen decrease as bioturbation began -- confirming the conclusions of the modelling. It is our hope that wider consideration of this feedback loop and the timing of its onset, will improve our understanding of the extent to which Earth's atmosphere-ocean oxygen reservoir is regulated." Co-author Professor Tim Lenton of the University of Exeter adds: "We already think this cycle was key to helping stabilise atmospheric oxygen during the Phanerozoic (the last 542 million years) -- and that oxygen stability is a good thing for the evolution of plants and animals. What is new in this study is it attributes the oxygen stabilisation to biology -- the presence or absence of animals stirring up the ocean sediments." Earlier this year, researchers from the Nordic Center for Earth Evolution showed that early animals may have needed surprisingly little oxygen to grow, supporting the theory that rising oxygen levels were not crucial for animal life to evolve on Earth. 

Source: University of Southern Denmark

 [August 06, 2014]

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HELICOCYSTIS

Bizarre 500-million-year-old creature unearthed

A new fossilized, cigar-shaped creature that lived about 520 million years ago has been unearthed in Morocco.

The 520-million year old fossilized creature that is one of the earliest known echinoderms
with fivefold symmetry [Credit: Andrew Smith, Proc. Royal Soc. B]

The newfound species, Helicocystis moroccoensis, has "characteristics that place it as the most primitive echinoderm that has fivefold symmetry," said study co-author Andrew Smith, a paleontologist at the Natural History Museum in London, referring to the group of animals that includes starfish and sea urchins. Modern echinoderms typically have five-point symmetry, such as the five arms of the starfish or the sand dollar's distinctive pattern.
The primitive sea creature, described on June 25 in the journal Proceedings of the Royal Society B, could even change its body shape from slender to stumpy. Researchers say it is a transitional animal that could help explain how early echinoderms evolved their unique body plans, Smith said.
Cambrian explosion
In 2012, Smith and his colleagues were excavating in sediments dating to about 520 million years ago in the Anti-Atlas Mountains in Morocco, when they uncovered several specimens of the strange fossil.

Artist's reconstruction of  the Helcocystis moroccoensis flourished
[Credit: Andrew Smith]

The creature lived on the ancient supercontinent called Gondwana during the Cambrian Explosion, a period when all creatures inhabited the seas and life on the planet diversified dramatically.
One of the oldest known echinoderms, Helicoplacus — first unearthed in the White Mountains in California — had a spiral but asymmetrical body plan. And all modern echinoderms start off as larvae with bilateral symmetry, raising the question of how and when the creatures' distinctive five-point body plan originated.
New creatures
H. moroccoensis, named after the country where it was found, had a cylindrical body that extended up to 1.6 inches (4 centimeters) long. The echinoderm's mouth was on the top of its body, and it sported a cup made of checkered plates with a small stem at its base. It had a latticelike skeleton made of calcite.
"It's a cigar-shaped beast, and it was able to expand and contract that cigar shape," Smith told LiveScience. "Sometimes it could be short and fat, and sometimes it could be long and thin."
The tiny sea creatures changed shape using a spiraling arrangement of five ambulacra, or grooves coming from the mouth that opened and closed to capture bits of food floating in the water.
The newly discovered species is the oldest known echinoderm with five ambulacra, and could shed light on how echinoderms evolved their unique body plans, Smith said.
H. moroccoensis was also found in sediments containing several other bizarre echinoderms, many of which had wacky body plans, ranging from completely asymmetrical to bilaterally symmetrical. That wide variety suggests the creatures were going through a period of dramatic diversification around that time period, Smith said.
"The important thing about the whole fauna is that there is already, by this time, a remarkable diversity in body form," Smith said. "And yet this is only 10 [million] to 15 million years after the calcite skeleton evolved."

Author: Tia Ghose | Source: LiveScience [June 25, 2013]