Researchers unveil mysteries of ancient Earth

A team of researchers has made strides in understanding the formation of massif-type anorthosites, enigmatic rocks that only formed during the middle part of Earth's history. These plagioclase-rich igneous rock formations, which can cover areas as large as 42,000 square kilometers and host titanium ore deposits, have puzzled scientists for decades due to conflicting theories about their origins.

A new study published in Science Advances on Aug. 14 highlights the intricate connections between Earth's evolving mantle and crust and the tectonic forces that have shaped the planet throughout its history. It also provides new ways to explore when plate tectonics began, how subduction dynamics operated billions of years ago and the evolution of Earth's crust.

The research team, led by Rice's Duncan Keller and Cin-Ty Lee, studied massif-type anorthosites to test ideas about the magmas that formed them. The research focused on the Marcy and Morin anorthosites, classic examples from North America's Grenville orogen that are about 1.1 billion years old.

By analyzing the isotopes of boron, oxygen, neodymium and strontium in the rocks as well as conducting petrogenetic modeling, the researchers discovered that the magmas that formed these anorthosites were rich in melts derived from oceanic crust altered by seawater at low temperatures. They also found isotopic signatures corresponding to other subduction zone rocks such as abyssal serpentinite.

"Our research indicates that these giant anorthosites likely originated from the extensive melting of subducted oceanic crust beneath convergent continental margins," said Keller, the Clever Planets Postdoctoral Research Associate, Earth, Environmental and Planetary Sciences and the study's lead author. "Because the mantle was hotter in the past, this process directly connects the formation of massif-type anorthosites to Earth's thermal and tectonic evolution."

The study, which combines classical methods with the novel application of boron isotopic analysis to massif-type anorthosites, suggests that these rocks formed during very hot subduction that may have been prevalent billions of years ago.

Because massif-type anorthosites don't form on Earth today, the new evidence linking these rocks to very hot subduction on the early Earth opens new interdisciplinary approaches for understanding how these rocks chronicle the physical evolution of our planet.

"This research advances our understanding of ancient rock formations and sheds light on the broader implications for Earth's tectonic and thermal history," said Lee, the Harry Carothers Wiess Professor of Geology, professor of Earth, environmental and planetary sciences and study co-author.

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On ancient Earth, it never rained but it poured

Today, we are experiencing the dramatic impacts that even a small increase in global temperatures can have on a planet's climate. Now, imagine an Earth 20 to 30 degrees Fahrenheit hotter than today. Earth likely experienced these temperatures at various times in the distant past and will experience them again hundreds of millions of years from now as the sun continues to brighten.

Little is known about how the atmosphere and climate behaved during these so-called hothouse periods. In a new study, researchers from Harvard University found that during these epochs of extreme heat, Earth may have experienced cycles of dryness followed by massive rain storms hundreds of miles wide that could dump more than a foot of rain in a matter of hours.

"If you were to look at a large patch of the deep tropics today, it's always raining somewhere," said Jacob Seeley, a Postdoctoral Fellow in Environmental Science and Engineering at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the Department of Earth and Planetary Science at Harvard and first author of the paper. "But we found that in extremely warm climates, there could be multiple days with no rain anywhere over a huge part of the ocean. Then, suddenly, a massive rainstorm would erupt over almost the entire domain, dumping a tremendous amount of rain. Then it would be quiet for a couple of days and repeat."

"This episodic cycle of deluges is a new and completely unexpected atmospheric state" said Robin Wordsworth, the Gordon McKay Professor of Environmental Science and Engineering at SEAS and senior author of the study.

The research not only sheds light on Earth's distant past and far-flung future but may also help to understand the climates of exoplanets orbiting distant stars.

The research is published in Nature.

In an atmospheric model, Seeley and Wordsworth cranked up Earth's sea surface temperature to a scalding 130 degrees Fahrenheit, either by adding more CO2 -- about 64-times the amount currently in the atmosphere -- or by increasing the brightness of the sun by about 10 percent.

At those temperatures, surprising things start happening in the atmosphere. When the air near the surface becomes extremely warm, absorption of sunlight by atmospheric water vapor heats the air above the surface and forms what's known as an "inhibition layer," a barrier that prevents convective clouds from rising into the upper atmosphere and forming rain clouds.

Instead, all that evaporation gets stuck in the near-surface atmosphere.

At the same time, clouds form in the upper atmosphere, above the inhibition layer, as heat is lost to space. The rain produced in those upper-level clouds evaporates before reaching the surface, returning all that water to the system.

"It's like charging a massive battery," said Seeley. "You have a ton of cooling high in the atmosphere and a ton of evaporation and heating near the surface, separated by this barrier. If something can break through that barrier and allow the surface heat and humidity to break into the cool upper atmosphere, it's going to cause an enormous rainstorm."

That's exactly what happens. After several days, the evaporative cooling from the upper atmosphere's rainstorms erodes the barrier, triggering an hours-long deluge. In one simulation, the researchers observed more rainfall in a six-hour period than some tropical cyclones drop in the U.S. across several days.

After the storm, the clouds dissipate, and precipitation stops for several days as the atmospheric battery recharges and the cycle continues.

"Our research goes to show that there are still a lot of surprises in the climate system," said Seeley. "Although a 30-degree increase in sea surface temperatures is way more than is being predicted for human-caused climate change, pushing atmospheric models into unfamiliar territory can reveal glimpses of what the Earth is capable of."

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Ancient asteroid impacts created the ingredients of life on Earth and Mars

A new study reveals that asteroid impact sites in the ocean may possess a crucial link in explaining the formation of the essential molecules for life. The study discovered the emergence of amino acids that serve as the building blocks for proteins -- demonstrating the role of meteorites in bringing life's molecules to earth, and potentially Mars.

There are two explanations for the origins of life's building molecules: extraterrestrial delivery, such as via meteorites; and endogenous formation. The presence of amino acids and other biomolecules in meteorites points to the former.

Researchers from Tohoku University, National Institute for Materials Science (NIMS), Center for High Pressure Science & Technology Advanced Research (HPSTAR), and Osaka University simulated the reactions involved when a meteorite crashes into the ocean. To do this, they investigated the reactions between carbon dioxide, nitrogen, water, and iron in a laboratory impact facility using a single stage propellant gun. Their simulation revealed the formation of amino acids such as glycine and alanine. These amino acids are direct constituents of proteins, which catalyze many biological reactions.

The team used carbon dioxide and nitrogen as the carbon and nitrogen sources because these gases are regarded as the two major components in the atmosphere on the Hadean Earth, which existed more than 4 billion years ago.

Corresponding author from Tohoku University, Yoshihiro Furukawa, explains, "Making organic molecules form reduced compounds like methane and ammonia are not difficult, but they are regarded as minor components in the atmosphere at that time." He adds, "The finding of amino acid formation from carbon dioxide and molecular nitrogen demonstrates the importance in making life's building blocks from these ubiquitous compounds."

The hypothesis that an ocean once existed on Mars also raises interesting avenues for exploration. Carbon dioxide and nitrogen are likely to have been the major constituent gases of the Martian atmosphere when the ocean existed. Therefore, impact-induced amino acid formation also provides a possible source of life's ingredients on ancient Mars.

Furukawa says, "further investigations will reveal more about the role meteorites played in bringing more complex biomolecules to Earth and Mars."

From Science Daily

How ancient microbes created massive ore deposits, set stage for early life

Lake Kivu

New research in Science Advances is uncovering the vital role that Precambrian-eon microbes may have played in two of the early Earth's biggest mysteries.

University of British Columbia (UBC) researchers, and collaborators from the universities of Alberta, Tübingen, Autònoma de Barcelona and the Georgia Institute of Technology, found that ancestors of modern bacteria cultured from an iron-rich lake in Democratic Republic of Congo could have been key to keeping Earth's dimly lit early climate warm, and in forming the world's largest iron ore deposits billions of years ago.

The bacteria have special chemical and physical features that in the complete absence of oxygen allow them to convert energy from sunlight into rusty iron minerals and into cellular biomass. The biomass ultimately causes the production of the potent greenhouse gas methane by other microbes.

"Using modern geomicrobiological techniques, we found that certain bacteria have surfaces which allow them to expel iron minerals, making it possible for them to export these minerals to the seafloor to make ore deposits," said Katharine Thompson, lead author of the study and PhD student in the department of microbiology and immunology.

"Separated from their rusty mineral products, these bacteria then go on to feed other microbes that make methane. That methane is what likely kept Earth's early atmosphere warm, even though the sun was much less bright than today."

This is a possible explanation to the 'faint-young-sun' paradox, originated by astronomer Carl Sagan. The paradox is that there were liquid oceans on early Earth, yet heat budgets calculated from the early Sun's luminosity and modern atmospheric chemistry imply Earth should have been entirely frozen. A frozen Earth would not have supported very much life. A methane-rich atmosphere formed in connection to large-scale iron ore deposits and life was initially proposed by University of Michigan atmospheric scientist James Walker in 1987. The new study provides strong physical evidence to support the theory and finds that microscale bacterial-mineral interactions were likely responsible.

"The fundamental knowledge we're gaining from studies using modern geomicrobiological tools and techniques is transforming our view of Earth's early history and the processes that led to a planet habitable by complex life including humans," said senior author of the paper, Sean Crowe, Canada Research Chair in Geomicrobiology and associate professor at UBC.

"This knowledge of the chemical and physical processes through which bacteria interact with their surroundings can also be used to develop and design new processes for resource recovery, novel building and construction materials, and new approaches to treating disease."

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In hot pursuit of dinosaurs: Tracking extinct species on ancient Earth via biogeography

Dinosaurs illustration.

One researcher at the University of Tokyo is in hot pursuit of dinosaurs, tracking extinct species around ancient Earth. Identifying the movements of extinct species from millions of years ago can provide insights into ancient migration routes, interaction between species, and the movement of continents.

"If we find fossils on different continents from closely related species, then we can guess that at some point there must have been a connection between those continents," said Tai Kubo, Ph.D., a postdoctoral researcher affiliated with the University Museum at the University of Tokyo.

A map of life -- biogeography

Previous studies in biogeography -- the geographic distribution of plants and animals -- had not considered the evolutionary relationships between ancient species. The new method that Kubo designed, called biogeographical network analysis, converts evolutionary relationships into geographical relationships.

For example, cats and dogs are more closely related to each other than to kangaroos. Therefore, a geographical barrier must have separated the ancestors of kangaroos from the ancestors of cats and dogs well before cats and dogs became separate species.

Most fossils are found in just a few hot-spot locations around the world and many ancient species with backbones (vertebrates) are known from just one fossil of that species. These limitations mean that a species' fossils cannot reveal the full area of where it was distributed around the world.

"Including evolutionary relationships allows us to make higher resolution maps for where species may have migrated," said Kubo.

The analysis used details from evolutionary studies, the location of fossil dig sites, and the age of the fossils. Computer simulations calculated the most likely scenarios for the migration of species between continents on the Cretaceous-era Earth, 145 to 66 million years ago.

North and south divide

This new analysis verified what earlier studies suggested: nonavian dinosaurs were divided into a group that lived in the Northern Hemisphere and another that lived in the Southern Hemisphere, and that those two groups could still move back and forth between Europe and Africa during the Early Cretaceous period (145 to 100 million years ago), but became isolated in the Late Cretaceous period (100 to 66 million years ago).

During the Early Cretaceous period, there were three major supercontinents: North America-Europe-Asia, South America-Africa, and Antarctica-India-Australia.

By the Late Cretaceous period, only the North America-Europe-Asia supercontinent remained. The other supercontinents had separated into the continents we know today, although they had not yet drifted to their current locations.

"During the Late Cretaceous period, high sea levels meant that Europe was a series of isolated islands. It makes sense that nonavian dinosaur species differentiated between Africa and Europe during that time," said Kubo.

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Arsenic-breathing life discovered in the tropical Pacific Ocean

Jaclyn Saunders (far right) fixes the line on a McLane instrument that pumps large volumes of seawater in order to extract the DNA. The instrument on the left measures properties such as temperature, salinity and depth and collects smaller samples of seawater.

Arsenic is a deadly poison for most living things, but new research shows that microorganisms are breathing arsenic in a large area of the Pacific Ocean. A University of Washington team has discovered that an ancient survival strategy is still being used in low-oxygen parts of the marine environment.

"Thinking of arsenic as not just a bad guy, but also as beneficial, has reshaped the way that I view the element," said first author Jaclyn Saunders, who did the research for her doctoral thesis at the UW and is now a postdoctoral fellow at the Woods Hole Oceanographic Institution and the Massachusetts Institute of Technology.

The study was published this week in the Proceedings of the National Academy of Sciences.

"We've known for a long time that there are very low levels of arsenic in the ocean," said co-author Gabrielle Rocap, a UW professor of oceanography. "But the idea that organisms could be using arsenic to make a living -- it's a whole new metabolism for the open ocean."

The researchers analyzed seawater samples from a region below the surface where oxygen is almost absent, forcing life to seek other strategies. These regions may expand under climate change.

"In some parts of the ocean there's a sandwich of water where there's no measureable oxygen," Rocap said. "The microbes in these regions have to use other elements that act as an electron acceptor to extract energy from food."

The most common alternatives to oxygen are nitrogen or sulfur. But Saunders' early investigations suggested arsenic could also work, spurring her to look for the evidence.

The team analyzed samples collected during a 2012 research cruise to the tropical Pacific, off the coast of Mexico. Genetic analyses on DNA extracted from the seawater found two genetic pathways known to convert arsenic-based molecules as a way to gain energy. The genetic material was targeting two different forms of arsenic, and authors believe that the pathways occur in two organisms that cycle arsenic back and forth between different forms.

Results suggest that arsenic-breathing microbes make up less than 1% of the microbe population in these waters. The microbes discovered in the water are probably distantly related to the arsenic-breathing microbes found in hot springs or contaminated sites on land.

"What I think is the coolest thing about these arsenic-respiring microbes existing today in the ocean is that they are expressing the genes for it in an environment that is fairly low in arsenic," Saunders said. "It opens up the boundaries for where we could look for organisms that are respiring arsenic, in other arsenic-poor environments."

Biologists believe the strategy is a holdover from Earth's early history. During the period when life arose on Earth, oxygen was scarce in both the air and in the ocean. Oxygen became abundant in Earth's atmosphere only after photosynthesis became widespread and converted carbon dioxide gas into oxygen.

Early lifeforms had to gain energy using other elements, such as arsenic, which was likely more common in the oceans at that time.

"We found the genetic signatures of pathways that are still there, remnants of the past ocean that have been maintained until today," Saunders said.

Arsenic-breathing populations may grow again under climate change. Low-oxygen regions are projected to expand, and dissolved oxygen is predicted to drop throughout the marine environment.

"For me, it just shows how much is still out there in the ocean that we don't know," Rocap said. Saunders recently collected more water samples from the same region and is now trying to grow the arsenic-breathing marine microbes in a lab in order to study them more closely.

"Right now we've got bits and pieces of their genomes, just enough to say that yes, they're doing this arsenic transformation," Rocap said. "The next step would be to put together a whole genome and find out what else they can do, and how that organism fits into the environment."

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