Welcome to GeoUnion, the graduate student body of the Department of Earth, Environmental and Planetary Sciences. GeoUnion strives to supplement the overall graduate student experience at Rice and DEEPS. GeoUnion represents DEEPS in the overall Rice grad student community, acts as a liaison between students and faculty and organizes a number of intra- and inter-departmental events throughout the academic year.
HOUSTON – (Jan. 21, 2021) – Where did Earth’s nitrogen come from? Rice University scientists show one primordial source of the indispensable building block for life was close to home.
The isotopic signatures of nitrogen in iron meteorites reveal that Earth likely gathered its nitrogen not only from the region beyond Jupiter’s orbit but also from the dust in the inner protoplanetary disk.
Nitrogen is a volatile element that, like carbon, hydrogen and oxygen, makes life on Earth possible. Knowing its source offers clues to not only how rocky planets formed in the inner part of our solar system but also the dynamics of far-flung protoplanetary disks.
The study by Rice graduate student and lead author Damanveer Grewal, Rice faculty member Rajdeep Dasgupta and geochemist Bernard Marty at the University of Lorraine, France, appears in Nature Astronomy.
Their work helps settle a prolonged debate over the origin of life-essential volatile elements in Earth and other rocky bodies in the solar system.
“Researchers have always thought that the inner part of the solar system, within Jupiter’s orbit, was too hot for nitrogen and other volatile elements to condense as solids, meaning that volatile elements in the inner disk were in the gas phase,” Grewal said.
Because the seeds of present-day rocky planets, also known as protoplanets, grew in the inner disk by accreting locally sourced dust, he said it appeared they did not contain nitrogen or other volatiles, necessitating their delivery from the outer solar system. An earlier study by the team suggested much of this volatile-rich material came to Earth via the collision that formed the moon.
But new evidence clearly shows only some of the planet’s nitrogen came from beyond Jupiter.
In recent years, scientists have analyzed nonvolatile elements in meteorites, including iron meteorites that occasionally fall to Earth, to show dust in the inner and outer solar system had completely different isotopic compositions.
“This idea of separate reservoirs had only been developed for nonvolatile elements,” Grewal said. “We wanted to see if this is true for volatile elements as well. If so, it can be used to determine which reservoir the volatiles in present-day rocky planets came from.”
Iron meteorites are remnants of the cores of protoplanets that formed at the same time as the seeds of present-day rocky planets, becoming the wild card the authors used to test their hypothesis.
The researchers found a distinct nitrogen isotopic signature in the dust that bathed the inner protoplanets within about 300,000 years of the formation of the solar system. All iron meteorites from the inner disk contained a lower concentration of the nitrogen-15 isotope, while those from the outer disk were rich in nitrogen-15.
This suggests that within the first few million years, the protoplanetary disk divided into two reservoirs, the outer rich in the nitrogen-15 isotope and the inner rich in nitrogen-14.
“Our work completely changes the current narrative,” Grewal said. “We show that the volatile elements were present in the inner disk dust, probably in the form of refractory organics, from the very beginning. This means that contrary to current understanding, the seeds of the present-day rocky planets — including Earth — were not volatile-free.”
Dasgupta said the finding is significant to those who study the potential habitability of exoplanets, a topic of great interest to him as principal investigator of CLEVER Planets, a NASA-funded collaborative project exploring how life-essential elements might come together on distant exoplanets.
“At least for our own planet, we now know the entire nitrogen budget does not come only from outer solar system materials,” said Dasgupta, Rice’s Maurice Ewing Professor of Earth, Environmental and Planetary Sciences.
“Even if other protoplanetary disks don’t have the kind of giant planet migration resulting in the infiltration of volatile-rich materials from the outer zones, their inner rocky planets closer to the star could still acquire volatiles from their neighboring zones,” he said.
A NASA FINESST grant, a NASA Science Mission Directorate grant to support CLEVER Planets, the European Research Council, and the Lodieska Stockbridge Vaughan Fellowship at Rice supported the research.
Read the abstract at https://www.nature.com/articles/s41550-020-01283-y.
Follow Rice News and Media Relations via Twitter @RiceUNews.
Planetary collision that formed the moon made life possible on Earth: https://news.rice.edu/2019/01/23/planetary-collision-that-formed-the-moon-made-life-possible-on-earth-2/
What recipes produce a habitable planet?: https://news.rice.edu/2018/09/17/what-recipes-produce-a-habitable-planet-2/
Breathing? Thank volcanoes, tectonics and bacteria: https://news.rice.edu/2019/12/02/breathing-thank-volcanoes-tectonics-and-bacteria/
ExPeRT: Experimental Petrology Rice Team (Dasgupta group): https://www.dasgupta.rice.edu/expert/people/dasgupta
CLEVER Planets: http://cleverplanets.org
Rice Earth, Environmental and Planetary Sciences: https://earthscience.rice.edu
Wiess School of Natural Sciences: https://www.rice.edu
Images for download:
The solar protoplanetary disk was separated into two reservoirs, with the inner solar system material having a lower concentration of nitrogen-15 and the outer solar system material being nitrogen-15 rich. The nitrogen isotope composition of present-day Earth lies in between, according to a new Rice University study that shows it came from both reservoirs. (Credit: Illustration by Amrita P. Vyas)
Rice University graduate student and lead author Damanveer Grewal, seated, with faculty member Rajdeep Dasgupta, conducted the study on nitrogen isotope compositions of iron meteorites to show volatile elements deposited on Earth and other rocky planets in the early solar system had more than one source. (Credit: Jeff Fitlow/Rice University)
An artist’s conception shows a protoplanetary disk of dust and gas around a young star. New research by Rice University shows that Earth’s nitrogen came from both inner and outer regions of the disk that formed our solar system, contrary to earlier theory. (Credit: NASA/JPL-Caltech)
Authors: Damanveer S. Grewal, Rajdeep Dasgupta, & Bernard Marty
Abstract: Understanding the origin of life-essential volatiles such as nitrogen (N) in the Solar System and beyond is critical to evaluate the potential habitability of rocky planets. Whether the inner Solar System planets accreted these volatiles from their inception or had an exogenous delivery from the outer Solar System is, however, not well understood. Using previously published data of nucleosynthetic anomalies of nickel, molybdenum, tungsten and ruthenium in iron meteorites along with their 15N/14 N ratios, here we show that the earliest formed protoplanets in the inner and outer protoplanetary disk accreted isotopically distinct N. While the Sun and Jupiter captured N from nebular gas6, concomitantly growing protoplanets in the inner and outer disk possibly sourced their N from organics and/or dust—with each reservoir having a different N isotopic composition. A distinct N isotopic signature of the inner Solar System protoplanets coupled with their rapid accretion suggests that non-nebular, isotopically processed N was ubiquitous in their growth zone between 0 and ~0.3 Myr after Solar System formation. Because the 15N/14N ratio of the bulk silicate Earth falls between that of the inner and outer Solar System reservoirs, we infer that N in the present-day rocky planets represents a mixture of both inner and outer Solar System material.
Grewal, D.S., Dasgupta, R. & Marty, B. A very early origin of isotopically distinct nitrogen in inner Solar System protoplanets. Nat Astron (2021). https://doi.org/10.1038/s41550-020-01283-y
– JANUARY 20, 2021
Crater study offers window on temperatures 3.5 billion years ago
HOUSTON – (Jan. 20, 2021) – Once upon a time, seasons in Gale Crater probably felt something like those in Iceland. But nobody was there to bundle up more than 3 billion years ago.
The ancient Martian crater is the focus of a study by Rice University scientists comparing data from the Curiosity rover to places on Earth where similar geologic formations have experienced weathering in different climates.
Iceland’s basaltic terrain and cool weather, with temperatures typically less than 38 degrees Fahrenheit, turned out to be the closest analog to ancient Mars. The study determined that temperature had the biggest impact on how rocks formed from sediment deposited by ancient Martian streams were weathered by climate.
The study by postdoctoral alumnus Michael Thorpe and Martian geologist Kirsten Siebach of Rice and geoscientist Joel Hurowitz of State University of New York at Stony Brook set out to answer questions about the forces that affected sands and mud in the ancient lakebed.
Data collected by Curiosity during its travels since landing on Mars in 2012 provide details about the chemical and physical states of mudstones formed in an ancient lake, but the chemistry does not directly reveal the climate conditions when the sediment eroded upstream. For that, the researchers had to look for similar rocks and soils on Earth to find a correlation between the planets.
The study published in JGR Planets takes data from well-known and varying conditions in Iceland, Idaho and around the world to see which provided the best match for what the rover sees and senses in the crater that encompasses Mount Sharp.
The crater once contained a lake, but the climate that allowed water to fill it is the subject of a long debate. Some argue that early Mars was warm and wet, and that rivers and lakes were commonly present. Others think it was cold and dry and that glaciers and snow were more common.
“Sedimentary rocks in Gale Crater instead detail a climate that likely falls in between these two scenarios,” said Thorpe, now a Mars sample return scientist at NASA Johnson Space Center contractor Jacobs Space Exploration Group. “The ancient climate was likely frigid but also appears to have supported liquid water in lakes for extended periods of time.”
The researchers were surprised that there was so little weathering of rocks on Mars after more than 3 billion years, such that the ancient Mars rocks were comparable to Icelandic sediments in a river and lake today.
“On Earth, the sedimentary rock record does a fantastic job of maturing over time with the help of chemical weathering,” Thorpe noted. “However, on Mars we see very young minerals in the mudstones that are older than any sedimentary rocks on Earth, suggesting weathering was limited.”
The researchers directly studied sediments from Idaho and Iceland, and compiled studies of similar basaltic sediments from a range of climates around the world, from Antarctica to Hawaii, to bracket the climate conditions they thought were possible on Mars when water was flowing into Gale Crater.
“Earth provided an excellent laboratory for us in this study, where we could use a range of locations to see the effects of different climate variables on weathering, and average annual temperature had the strongest effect for the types of rocks in Gale Crater,” said Siebach, a member of the Curiosity team who will be a Perseverance operator after the new lander touches down in February. “The range of climates on Earth allowed us to calibrate our thermometer for measuring the temperature on ancient Mars.”
The makeup of sand and mud in Iceland were the closest match to Mars based on analysis via the standard chemical index of alteration (CIA), a basic geological tool used to infer past climate from chemical and physical weathering of a sample.
“As water flows through rocks to erode and weather them, it dissolves the most soluble chemical components of the minerals that form the rocks,” Siebach said. “On Mars, we saw that only a small fraction of the elements that dissolve the fastest had been lost from the mud relative to volcanic rocks, even though the mud has the smallest grain size and is usually the most weathered.
“This really limits the average annual temperature on Mars when the lake was present, because if it were warmer, then more of those elements would have been flushed away,” she said.
The results also indicated the climate shifted over time from Antarctic-like conditions to become more Icelandic while fluvial processes continued to deposit sediments in the crater. This shift shows the technique can be used to help track climate changes on ancient Mars.
While the study focused on the lowest, most ancient part of the lake sediments Curiosity has explored, other studies have also indicated the Martian climate probably fluctuated and became drier with time. “This study establishes one way to interpret that trend more quantitatively, by comparison to climates and environments we know well on Earth today,” Siebach said. “Similar techniques could be used by Perseverance to understand ancient climate around its landing site at Jezero Crater.”
In parallel, climate change, especially in Iceland, may shift the places on Earth best-suited for understanding the past on both planets, she said.
Siebach is an assistant professor of Earth, environmental and planetary sciences at Rice. Hurowitz is an associate professor of geosciences at Stony Brook.
A NASA postdoctoral fellowship to Thorpe, the NASA Solar System Workings program and the David E. King Field Work Award from Stony Brook supported the research.
Read the abstract at https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020JE006530.
Follow Rice News and Media Relations via Twitter @RiceUNews.
Siebach Lab: https://kirstensiebach.com/lab
Michael Thorpe: https://mikethorpe.weebly.com/
Mars Science Laboratory Curiosity: https://mars.nasa.gov/msl/home/
Mars 2020: Perseverance: https://mars.nasa.gov/mars2020/
Department of Earth, Environmental and Planetary Sciences: https://earthscience.rice.edu
Wiess School of Natural Sciences: https://naturalsciences.rice.edu
Images for download:
Weathering of sedimentary rock at Gale Crater likely happened under Iceland-like temperatures more than 3 billion years ago, when water still flowed on Mars. Rice University researchers compared data collected by the Curiosity rover, correlated with conditions at various places on Earth, to make their determination. (Credit: NASA)
A river-fed sedimentary plain in Iceland bears resemblance to what might have fed Mars’ Gale Crater more than 3 billion years ago. Researchers at Rice University studied rover data on sedimentary rocks at the crater and compared them to similar formations on Earth to determine what the climate might have been like at the crater when the sediments were deposited. (Credit: Photo by Michael Thorpe)
CAPTION: Michael Thorpe. (Credit: Wiess School of Natural Sciences/Rice University)
CAPTION: Kirsten Siebach. (Credit: Rice University)
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