Chaotic flows and the origin of life

A research team at Texas A&M University has uncovered a physical mechanism that may help answer one of the major questions concerning the origin of life, "How did the building blocks form?"

Chaotic advection accelerates interfacial transport under hydrothermally relevant conditions 
[Credit: Proceedings of the National Academy of Sciences]

The research team is led by Dr. Victor Ugaz, professor and holder of the Charles D. Holland '53 Professorship and the Thaman Professorship in the Artie McFerrin Department of Chemical Engineering. The team also includes Dr. Yassin A. Hassan, professor and holder of the Sallie & Don Davis '61 Professorship and department head of the Department of Nuclear Engineering.

Scientists have long known that the building blocks of life – amino acids, nucleobases and sugars – were present in the early ocean, but they were very low in concentration. In order for life to emerge, these building blocks needed to be combined and enriched into long-chain macromolecules. Identifying the process and mechanism driving this synthesis has been one of the largest questions concerning the origin of life.

"In the early ocean, those building blocks were present in the environment," Ugaz said. "They were there, but they were so dilute; there is a question about how they combined. So one area of interest is what kind of concentration mechanism could have existed to enrich those components to a point where they could start to form longer chains, more complex molecules."

In an article appearing in Proceedings of the National Academy of Sciences, the Texas A&M research team describes a mechanism that may have played a major role in combining these dilute chemical building blocks into the long-chain macromolecules necessary for life.

The research team explored this by creating a model system of cylindrical cells that mimic the structure of pores in mineral formations found near a recently discovered, new type of subsea hydrothermal vent. The temperature gradients present within these vents function just like an ordinary lava lamp, circulating fluid within the tiny pore spaces. The team found that these flows are surprisingly complex and chaotic – meaning that individual paths follow a rough general pattern, but no trajectories are identical. This discovery made it possible to identify conditions where these flows are able to provide bulk homogenization of the various organic molecules present in the vents, while at the same time transport them to catalytically active pore surfaces where they absorb and react.

According to Ugaz, there is an easy way to picture this phenomenon. "Imagine you are stirring coffee, and you put in some cream or something that would stick to the side of the cup. When you stir it a certain way, two things are actually happening at once: you are mixing the bulk of the liquid, but you are also making it go to a certain spot on the surface of the cup."

These flows naturally occur within hydrothermal pore networks providing an intriguing mechanism to explain how dilute organic precursors in the early ocean could have assembled into complex biomacromolecules. This has been one of the key unanswered questions in the origin of life on Earth, and in extraterrestrial systems where similar hydrothermal environments have been discovered. Beyond this finding, the research is significant in a number of other ways.

There are a whole host of different processes beyond the biotic and prebiotic chemistry that can be catalyzed in these environments. First, these porous formations play a major role in converting carbon dioxide into various carbonates. The exact mechanisms driving this carbon dioxide capture are not currently well described. However, the results of this study indicate that these chaotic flows may be able to help describe this phenomenon.

Further, with a better understanding of these flows and how they drive reactions at a surface, it is feasible that they could drive a new type of reactor. As the flows rely on heat differences, such a reactor could be entirely passive, utilizing waste heat to drive reactions.

Author: Drew Thompson | Source: Artie McFerrin Department of Chemical Engineering at Texas A&M University [April 14, 2017]

byUnknown

in Biology, Earth Science, Evolution, Oceans, Origin of Life

April 13, 2017

Chaotic flows and the origin of life

A research team at Texas A&M University has uncovered a physical mechanism that may help answer one of the major questions concerning th...

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First oceans may have been acidic

One way to understand how ocean acidity can change, for example, in response to rising carbon dioxide (CO2) levels, is to look to the history of seawater acidity. Dr. Itay Halevy of the Weizmann Institute of Science has looked to the distant past -- all the way back to Earth's earliest oceans. The model he developed, together with Dr. Aviv Bachan of Stanford University, suggests that the early oceans, right around the time that life originated, were somewhat acidic, and that they gradually became alkaline. The study, published in Science, sheds light on how past ocean acid levels were controlled by CO2 in the atmosphere, an important process for understanding the effects of climate change.

Dr. Itay Halevy of the Weizmann Institute of Science has looked to the distant past -- all the way back to Earth's earliest 
oceans. The model he developed, together with Dr. Aviv Bachan of Stanford University, suggests that the early oceans,
 right around the time that life originated, were somewhat acidic, and that they gradually became alkaline 
[Credit: Weizmann Institute of Science]

Acidity and alkalinity are measured on the pH scale of 0-14. On this scale, 7 is neutral, higher is alkaline, lower is acidic. At around 8.2, today's oceans are mildly alkaline, and we know that rising CO2 levels are currently increasing the oceans' acidity (decreasing pH).

Halevy, of the Weizmann Institute's Earth and Planetary Sciences Department, explains that billions of years ago "the early Sun was dimmer, even though we don't have evidence for a much colder climate. We think that this is because the early atmosphere had more of the greenhouse gas CO2 than at present, and that as the Sun got brighter, CO2 levels decreased," says Halevy.

CO2, and water produce carbonic acid, so it stands to reason that the early oceans would have been more acidic. But higher early CO2 levels would also have resulted in acidic rainwater and this, in turn, could have led to higher rates of chemical weathering of Earth's rocky crust, washing down ions that would partly neutralize the acidity of CO2. Which effect is the stronger? This has been unclear; thus previous models of the history of seawater pH have come up with everything from high values to low.

The model that Halevy and Bachan developed accounts for these processes and the way in which they influence the fluxes of ions into and out of ocean water. According to their model, the acidifying effect of higher CO2 levels dominated, and the early oceans had a lower-than-present pH.

"On a very fundamental level," says Bachan, "we show that the pH of the ocean has been controlled by a few simple processes for all of geologic time."

Putting numbers to the proposed pH, Halevy says that three to four billion years ago, the pH of ocean water was somewhere between 6.0 and 7.5 -- between that of milk and human blood. Halevy: "This gives us some clues as to the conditions under which life emerged in the early oceans."

"We had an early ocean more acidic than today in which primitive life thrived and chemical cycles were balanced; but if we want to apply this insight to today, we have to remember that this balance of acids and bases was maintained over geological timescales -- millions of years," he adds. "Today's acidification from CO2 is much more rapid, so this model does not apply to the short-term problem. Hundreds of thousands of years from now, the oceans will have found a new balance, but between now and then, marine organisms and environments may suffer."

Source: Weizmann Institute of Science [April 08, 2017]

byUnknown

in Ancient Environment, Climate Change, Earth Science, Oceans, Palaeontology

April 08, 2017

First oceans may have been acidic

One way to understand how ocean acidity can change, for example, in response to rising carbon dioxide (CO2) levels, is to look to the histor...

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Skeletons evolved as ocean chemistry changed

Skeletons and shells first came into being 550 million years ago as the chemical make-up of seawater changed, a study suggests.

Fieldwork at the Yudoma River in Siberia, Russia 
[Credit: Rachel Wood]

Ancient marine life may have developed from soft-bodied animals into creatures with hard body parts as oxygen levels rose and calcium and magnesium levels in prehistoric oceans changed, researchers say.

Until now, little was known about how skeletons and shells – which are made of calcium carbonate – first evolved, the team says. Previous theories suggested that soft-bodied organisms had undergone a mass extinction, which allowed organisms with skeletons and shells to flourish.

However, Edinburgh researchers have found that the earliest lifeforms with hard body parts co-existed with closely related soft-bodied species. The team examined a range of fossils unearthed from limestone rocks in Siberia, which formed millions of years ago from seawater with high levels of calcium carbonate.

Artist's impression of a Suvorevella fossil, one of the oldest known skeletal macrofossils 
[Credit: Alina Konovalenko]

They concluded that hard-bodied lifeforms were first present only in such environments where high levels of calcium carbonate allowed organisms to develop primitive hard parts. Around 10m years later, the diversity of life of Earth increased rapidly – a period known as the Cambrian explosion – and hard-bodied life began to thrive. An increased threat from predators led lifeforms to develop new, more complex hard parts in environments that were less carbonate-rich, the team says.

The development of hard body parts – through a process called biomineralisation – marked a significant evolutionary advance from the previous world of soft-bodied life, the team says. The study is published in the journal Proceedings of the Royal Society B. The research was carried out in collaboration with Lomonosov Moscow State University.

"How animals produced shells and skeletons is one of the major events in the evolution of life. We are only now starting to understand the processes underlying this revolution," says Professor Rachel Wood of the School of GeoSciences.

Source: University of Edinburgh [April 04, 2017]

byUnknown

in Earth Science, Fossils, Oceans, Palaeontology, Siberia

April 04, 2017

Skeletons evolved as ocean chemistry changed

Skeletons and shells first came into being 550 million years ago as the chemical make-up of seawater changed, a study suggests. Fieldwork at...

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