Tracking down the forces that shaped our Solar System's evolution
Discovery answers fundamental questions about Earth's geochemical history


Date:
December 22, 2021
Source:
Carnegie Institution for Science
Summary:
Meteorites are remnants of the building blocks that formed Earth
and the other planets orbiting our Sun. Recent analysis of their
isotopic makeup led settles a longstanding debate about the
geochemical evolution of our Solar System and our home planet.



FULL STORY ========================================================================== Meteorites are remnants of the building blocks that formed Earth and
the other planets orbiting our Sun. Recent analysis of their isotopic
makeup led by Carnegie's Nicole Nie and published in Science Advances
settles a longstanding debate about the geochemical evolution of our
Solar System and our home planet.


==========================================================================
In their youth, stars are surrounded by a rotating disk of gas and
dust. Over time, these materials aggregate to form larger bodies,
including planets. Some of these objects are broken up due to collisions
in space, the remnants of which sometimes hurtle through Earth's
atmosphere as meteorites.

By studying a meteorite's chemistry and mineralogy, researchers like
Nie and Carnegie's Anat Shahar can reveal details about the conditions
these materials were exposed to during the Solar System's tumultuous
early years. Of particular interest is why so-called moderately volatile elements are more depleted on Earth and in meteoritic samples than the
average Solar System, represented by the Sun's composition. They are named because their relatively low boiling points mean they evaporate easily.

It's long been theorized that periods of heating and cooling resulted
in the evaporation of volatiles from meteorites. Nie and her team showed
that an entirely different phenomenon is the culprit in the case of the
missing volatiles.

Solving the mystery involved studying a particularly primitive class
of meteorites called carbonaceous chondrites that contain crystalline
droplets, called chondrules, which were part of the original disk of
materials surrounding the young Sun. Because of their ancient origins,
these beads are an excellent laboratory for uncovering the Solar System's geochemical history.

"Understanding the conditions under which these volatile elements are
stripped from the chondrules can help us work backward to learn the
conditions they were exposed to in the Solar System's youth and all the
years since," Nie explained.



==========================================================================
She and her co-authors set out to probe the isotopic variability of
potassium and rubidium, two moderately volatile elements. The research
team included Shahar and colleagues from The University of Chicago,
where Nie was a graduate student prior to joining Carnegie -- Timo Hopp,
Justin Y. Hu, Zhe J. Zhang, and Nicolas Dauphas -- as well as Xin-Yang
Chen and Fang-Zhen Teng from University of Washington Seattle.

Each element contains a unique number of protons, but its isotopes
have varying numbers of neutrons. This means that each isotope has a
slightly different mass than the others. As a result, chemical reactions discriminate between the isotopes, which, in turn, affects the proportion
of that isotope in the reaction's end products.

"This means that the different kinds of chemical processing that the
chondrules experienced will be evident in their isotopic composition,
which is something we can probe using precision instruments," Nie added.

Their work enabled the researchers to settle the debate about how and
when in their lifespans the chondrules lost their volatiles. The isotopic record unveiled by Nie and her team indicates that the volatiles were
stripped as a result of massive shockwaves passing through the material circling the young Sun that likely drove melting of the dust to form
the chondrules. These types of events can be generated by gravitational instability or by larger baby planets moving through the nebular gas.

"Our findings offer new information about our Solar System's youth and
the events that shaped the geochemistry of the planets, including our
own," Nie concluded.

"The revelation that shockwaves modified the material from which the
planets were born has major implications for Earth science as well," added Carnegie Earth and Planets Laboratory Director Richard Carlson. "Once a
planet gets as big as ours, its gravity is sufficient that losing most
volatile elements becomes very difficult. Knowing that moderately volatile elements were stripped from the planetary building blocks themselves
answers fundamental questions about Earth's geochemical evolution."
This work was supported by NASA, a Carnegie postdoctoral fellowship,
and a Carnegie Postdoc x Postdoc seed grant.

========================================================================== Story Source: Materials provided by
Carnegie_Institution_for_Science. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Nicole X. Nie, Xin-Yang Chen, Timo Hopp, Justin Y. Hu, Zhe J. Zhang,
Fang-Zhen Teng, Anat Shahar, Nicolas Dauphas. Imprint of
chondrule formation on the K and Rb isotopic compositions of
carbonaceous meteorites. Science Advances, 2021; 7 (49) DOI:
10.1126/sciadv.abl3929 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211222153032.htm

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