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  • Cosmic Bombardment Created Potential for Prebiotic Chemistry Aaron Sidder
    Source: AGU Advances Asteroids and planetesimals regularly bombarded Earth between about 4.6 billion and 3.5 billion years ago, in the Hadean and Archean eons. Because few rocks today are more than 4 billion years old, our understanding of the planet’s environment during that time is limited. However, samples from the Moon and its cratered surface hint at the period’s rate of cosmic impacts. Early asteroid strikes were responsible for significant changes in Earth’s crust, which was primar
     
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Cosmic Bombardment Created Potential for Prebiotic Chemistry

✇Eos
By: Aaron Sidder
5 June 2026 at 12:02
Artist’s illustration of early Earth showing much of the planet covered with a gray, crater-pocked surface, while other areas are covered with blue water or outlined by glowing red lineaments representing molten rock.
Source: AGU Advances

Asteroids and planetesimals regularly bombarded Earth between about 4.6 billion and 3.5 billion years ago, in the Hadean and Archean eons. Because few rocks today are more than 4 billion years old, our understanding of the planet’s environment during that time is limited. However, samples from the Moon and its cratered surface hint at the period’s rate of cosmic impacts.

Early asteroid strikes were responsible for significant changes in Earth’s crust, which was primarily basalt-like at the time. The shock waves from collisions fractured the crust and increased porosity, allowing fluids and gases to move through the rocks. Prior research suggests that the resulting hydrothermal systems—such as the network of geysers around Yellowstone National Park—provided the environment for the origin and evolution of early life on Earth.

Alexander et al. explored how surface impacts during the Hadean and Archean allowed fluids and gases to maneuver through crustal environments. The authors built a large suite of impact simulations with the iSALE shock physics code, toggling parameters such as basalt crust thickness, geothermal gradients, and the presence or absence of a 5-kilometer-deep ocean. The simulations detailed how collisions on the surface shaped permeability in the crust. They then integrated a model for ancient bombardment data to understand the cumulative effects of repeated strikes over time.

The results indicate that prior to 4.3 billion years ago, impacts may have made the crust far more permeable, particularly in its top 8 kilometers. From the simulations, the authors inferred that the size of permeable regions was dependent on impact energy, and that geothermal gradients and rock composition in the crust affected the degree of fragmentation after impact. These porous domains formed potential settings for prebiotic chemistry within the early crust.

The research is the first comprehensive study of impact-generated permeability in early Earth’s outermost layer. The results provide a novel framework for evaluating how bombardment influenced hydrothermal circulation and geochemical alteration during the Hadean and Archean eons, with implications for our understanding of life’s origin and evolution in Earth’s earliest days. (AGU Advances, https://doi.org/10.1029/2025AV002097, 2026)

—Aaron Sidder, Science Writer

A photo of a telescope array appears in a circle over a field of blue along with the Eos logo and the following text: Support Eos’s mission to broadly share science news and research. Below the text is a darker blue button that reads “donate today.”
Citation: Sidder, A. (2026), Cosmic bombardment created potential for prebiotic chemistry, Eos, 107, https://doi.org/10.1029/2026EO260180. Published on 5 June 2026.
Text © 2026. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.
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  • Navigating the Past with Ancient Stone Compass Needles Aaron Sidder
    Source: Journal of Geophysical Research: Solid Earth Magnetic rocks with iron oxide concentrations act as natural chroniclers of Earth’s past continental movements. Using small samples of rocks, scientists can isolate magnetic grains that were frozen in orientation as the rock solidified. The magnetization of these grains acts as a miniature compass needle, pointing toward ancient magnetic poles. This same principle applies to extraterrestrial samples, such as meteorites and lunar rocks, whi
     
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Navigating the Past with Ancient Stone Compass Needles

✇Eos
By: Aaron Sidder
16 April 2026 at 13:09
A computer and keyboard on a desk sit next to a complex microscope that says “QDM” on the top.
Source: Journal of Geophysical Research: Solid Earth

Magnetic rocks with iron oxide concentrations act as natural chroniclers of Earth’s past continental movements. Using small samples of rocks, scientists can isolate magnetic grains that were frozen in orientation as the rock solidified. The magnetization of these grains acts as a miniature compass needle, pointing toward ancient magnetic poles. This same principle applies to extraterrestrial samples, such as meteorites and lunar rocks, which preserve evidence of the early solar nebula’s evolution.

However, traditional bottle cap–sized bulk samples often contain a mixture of reliable and unreliable magnetic signals, resulting in complex data that hamper interpretation. To improve accuracy, researchers have turned to magnetic microscopy. This technique maps magnetic fields at submillimeter to submicrometer scales in thinly sliced rock sections using advanced tools like a quantum diamond microscope (QDM) or a cryogenic superconducting quantum interference device microscope. By creating high-resolution maps of individual magnetic particles, scientists can reconstruct ancient fields with much higher precision while filtering out muddy signals from unstable grains.

Despite its potential, magnetic microscopy is an emerging field with its own set of uncertainties. To help constrain measurement data, Bellon et al. combined QDM observations with computer modeling to analyze how a magnetic particle’s stray field—the magnetic flux that leaks into the surrounding space—decays as it moves away from the source. They specifically investigated how a particle’s internal magnetic structure and external measurement noise affect the accuracy of these reconstructions.

The study found that in iron oxides, the smallest and most magnetically stable particles produce signals that are strong at the source but fade rapidly with distance. In contrast, larger particles produce signals that remain detectable farther away. This creates a challenge: The most stable grains for long-term geological data (the smallest ones) are the hardest to detect if the sensor is not perfectly positioned or if sensor interference is present.

By quantifying measurement error, the authors provide a road map for the field of micropaleomagnetism. Their findings could allow researchers to better account for uncertainty, leading to more robust reconstructions of Earth’s magnetic history and a deeper understanding of planetary evolution. (Journal of Geophysical Research: Solid Earth, https://doi.org/10.1029/2025JB033133, 2026)

—Aaron Sidder, Science Writer

A photo of a telescope array appears in a circle over a field of blue along with the Eos logo and the following text: Support Eos’s mission to broadly share science news and research. Below the text is a darker blue button that reads “donate today.”
Citation: Sidder, A. (2026), Navigating the past with ancient stone compass needles, Eos, 107, https://doi.org/10.1029/2026EO260122. Published on 16 April 2026.
Text © 2026. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.
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