Researchers refine estimate of amount of carbon in Earth's outer core


Date:
August 19, 2021
Source:
Florida State University
Summary:
New research is providing a better estimate of the amount of carbon
in the Earth's outer core, and the work suggests the core could
be the planet's largest reservoir of that element.



FULL STORY ==========================================================================
New research from Florida State University and Rice University is
providing a better estimate of the amount of carbon in the Earth's
outer core, and the work suggests the core could be the planet's largest reservoir of that element.


==========================================================================
The research, published in the journal Communications Earth & Environment, estimates that 0.3 to 2.0 percent of the Earth's outer core is carbon.

Though the percentage of carbon there is low, it's still an enormous
amount because the outer core is so large. The researchers estimated that
the outer core contains between 5.5 and 36.8 x 10^24 grams of carbon --
an immense number.

"Understanding the composition of the Earth's core is one of the key
problems in the solid-earth sciences," said co-author Mainak Mookherjee,
an associate professor of geology in the Department of Earth, Ocean and Atmospheric Science.

"We know the planet's core is largely iron, but the density of iron is
greater than that of the core. There must be lighter elements in the core
that reduce its density. Carbon is one consideration, and we are providing better constraints as to how much might be there." Previous research has estimated the total amount of carbon on the planet. This work refines
the estimates for the carbon content of Earth to a range between about
990 parts per million and more than 6,400 parts per million. That would
mean the core of the Earth -- which includes both the outer core and
the inner core -- could contain 93 to 95 percent of the planet's carbon.

Because humans can't access the Earth's core, they have to use indirect
methods to analyze it. The research team compared the known speed
of compressional sound waves traveling through the Earth to computer
models that simulated different compositions of iron, carbon and other
light elements at the pressure and temperature conditions of the Earth's
outer core.



========================================================================== "When the velocity of the sound waves in our simulations matched the
observed velocity of sound waves traveling through the Earth, we knew
the simulations were matching the actual chemical composition of the
outer core," said lead author and postdoctoral researcher Suraj Bajgain.

Scientists have attempted to give a range of the amount of carbon in the
outer core before. This research narrows that possible range by including
other light elements -- namely oxygen, sulfur, silicon, hydrogen and
nitrogen -- in the models estimating the outer core's composition.

Just like hydrogen and oxygen and other elements, carbon is a
life-essential element. It's part of what makes life possible on Earth.

"It's a natural question to ask where did this carbon that we are all
made of come from and how much carbon was originally supplied when the
Earth formed," Mookherjee said. "Where is the bulk of the carbon residing
now? How has it been residing and how has it transferred between different reservoirs? Understanding the total inventory of carbon is what this
study gives us insight to." Knowing how much carbon exists on Earth
will help scientists improve their understanding of the composition of
both our planet and rocky planets elsewhere in the universe.

"There have been a lot of activities over the last decade to determine the carbon budget of the Earth's core using cosmochemical and geochemical
models," said study co-author Rajdeep Dasgupta, the Maurice Ewing
Professor of Earth, Environmental and Planetary Sciences at Rice
University. "However, it remained an open question because of a lot of uncertain parameters on the accretion process and the building blocks of
rocky planets. What is neat about this study is that it provides a direct estimate on the Earth's outer core's present-day carbon budget. Therefore,
this will in turn help the community bracket the possible planetary
ingredients and the early processes better." The National Science
Foundation and NASA supported this research, and the Extreme Science and Engineering Discovery computing (XSEDE) and the Research Computing Center
(RCC) at FSU provided computing resources for this work.

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


========================================================================== Journal Reference:
1. Suraj K. Bajgain, Mainak Mookherjee, Rajdeep Dasgupta. Earth's
core could
be the largest terrestrial carbon reservoir. Communications Earth &
Environment, 2021; 2 (1) DOI: 10.1038/s43247-021-00222-7 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210819113059.htm

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