Hello everyone! April 22 is Earth Day–a celebration of our planet that dates back to 1970. While working on this edition of Core Elements, it dawned on me that geoscientists, by profession and passion, think of Earth almost every day. With this in mind, I hope you celebrate and appreciate our planet, and enjoy reading some recent developments in Earth science. Happy Earth Day!

Rasoul Sorkhabi

Editor, Core Elements

Rare-Earth Elements’ Journey to the Lithosphere

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Rare-earth elements are in high demand because of their numerous applications in modern tech. Smart phones, computer monitors, LED lights—they all require REEs.

Where do they come from?

• Nearly all REEs originate from alkaline-silicate rocks and carbonatites crystallized from mantle melts.

• Subduction of marine sediments beneath continental plates fertilizes the lithospheric mantle with REEs.

• The subcontinental mantle at subduction plate boundaries provides massive storage for REEs.

How do REEs get to the lithosphere?

• Experiments on REE-rich marine sediments show that mantle melting occurs at a pressure of 4 gigapascal and a temperature of 1000 degrees Celsius.

• But melting alone at hot subduction zones will not bring REEs to Earth’s lithosphere.

• Diapiric rise of the melts provides a substantial transport of REEs from the subducting slab to the lower lithosphere, according to a new study in Geology.   

Key takeaways:

• This study suggests that buoyancy and diapiric rise of mantle melts in the subduction wedge is a significant process for economic grade mineralization.

• It also implies that regions where protracted oceanic plate subduction has ceased are promising locations for exploration of REE-rich resources.

• Finally, the authors argue that carbonate minerals within subducting sediments facilitate formation of REE-rich diapirs. That is why nearly 50 percent of the global REE oxides are hosted in carbonatites.   

Why it matters: Understanding how REEs are enriched in rocks derived from the mantle provides key insight into REE exploration.

Go deeper: Read the full study by Zhu and colleagues at the Chinese Academy of Geological Sciences here.

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Clues About the Beginnings of Life on Earth

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Speaking of minerals—did they also play a role in the emergence of primordial cells on Earth? Many geologists think so, but of the thousands of minerals out there, which ones were key to Earth’s beginnings?

A recent article in Earth and Planetary Science Letters suggests olivine may be top among them.

Why olivine?

• The olive-colored mineral, with chemical structure (Mg,Fe)2SiO4, is the first mineral to crystallize from magma.

• Besides being a gemstone, olivine is a major player in deep earth and deep waters.

• Even though it is easily weathered at the Earth’s surface, olivine is abundant in the lithosphere-mantle interface.

Sugar rush: The key to discovering what may have happened during the origins of earthly life could lie in sugars.

Cells use sugars for energy and to build RNA and DNA molecules. But before the first cells could emerge, there must have been an abiotic evolution to prepare sugars for life.

Hypothesis: One possibility is that cells converted toxic formaldehyde into more complex and useful sugars—a process called formose reaction. Did olivine act as a catalyst in this reaction? This study aimed to find out.

Here’s what researchers did:

1. They reacted formaldehyde with olivine grains obtained from a rock sample collected in Arizona—interestingly, from a place called Peridot (another name for olivene).

2. The sample was thoroughly washed with solvents to remove any external organic contamination.

3. The mm-size olivine grains were placed in a reaction chamber filled with warm water to simulate the early Earth environment.

4. The experiment ran for 45 days, when reaction products were analyzed with gas chromatography.

Sweet results: The experiment showed that olivine did facilitate the formose reaction, and the product was glycolaldehyde—the simplest sugar molecule made from two molecules of formaldehyde.

Why it matters:

• The presence of olivine with hot seawater and organic compounds at hydrothermal vents indicates that olivine may hold some of the clues to life’s Earthly origins.

• Olivine and formaldehyde also occur in asteroids and cosmic dust. The implications of the new study go beyond Earth.

Dive deeper: Learn more about the study here.

A New App Makes Numerical Stratigraphic Correlation Easy

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As described by Simon Winchester in his bestseller The Map That Changed the World, stratigraphy in the early 19th century was the foundation of modern geology.

Today, stratigraphy is highly advanced and uses analytical techniques and numerical information such as elemental composition, stable isotope geochemistry, gamma ray logs, and so forth.

Modern challenge: A daunting challenge for stratigraphers is figuring out how to correlate large numerical data sets from various areas on a digital platform.

There’s an app for that: A recently published article in GSA Today showcases a user-friendly app for numeral stratigraphic correlation.

Called Align, the app includes a graphical user interface for uploading data and building alignment libraries as well as tools for output visualization and correlation.

How it works: The app is written in R language and utilizes dynamic time wrapping, an algorithm that achieves least-square alignments between two time-series of measurements.

Why it matters:

• As computational technologies have enabled quantitative tools for time-series analysis of data, correlation of stratigraphic databases from different regions have become crucial to our understanding of Earth’s history.

• The Align app for numerical stratigraphic correlation is free and can be accessed through Comprehensive R Archive Network (CRAN).

For more reading: Read the article by Hagen and coauthors online.

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