Introduction

Recent studies reveal that Earth is a complex mosaic of carbonaceous (CC) and non-carbonaceous (NC) materials. The isotopic signatures of meteorites, combined with data from the bulk silicate Earth (BSE), illustrate this intriguing mixture, suggesting a profound cosmic history influencing our planet's formation.

Variability of Carbonaceous Material in BSE

Research indicates that the ratio of CC material present in the BSE varies across different elements. This variation is influenced by each element's tendency to partition into metal and its volatility. Surprisingly, while a significant portion of Earth's accreted material is dominated by NC, it appears that CC material, enriched in moderately volatile elements by a factor of approximately 10, was delivered to Earth during the final stages of its accretion—about 2-10% before the planet fully formed.

Contrasts with Dynamical Models

This late delivery of CC material poses a fascinating contrast to existing dynamical models, which suggest that CC objects were implanted in the inner solar system early on, driven by the growth and migration of giant planets like Jupiter and Saturn. Furthermore, both Earth’s late veneer and Mars show NC dominance, pointing to a hypothesis that most material scattered inwards was concentrated in a few large CC embryos rather than numerous smaller planetesimals.

Hypothesis on CC Embryos

Our hypothesis posits that Earth was able to accrete several of these substantial CC embryos, while Mars, intriguingly, did not. At least one of these CC embryos is believed to have impacted our planet during the final stages of its formation, specifically when accretion was around 90-90% complete.

Implications on Earth's Mantle and Moon Formation

This theory aligns with the widely accepted giant impact hypothesis for the Moon's formation, which asserts that a large NC body collided with Earth. Crucially, this late impact scenario suggests that the collision did not completely homogenize the Earth's mantle, allowing distinct isotopic signatures to remain.

Conclusion

As researchers like Francis Nimmo, Thorsten Kleine, Alessandro Morbidelli, and David Nesvorny continue to dissect these processes, our understanding of Earth's formation becomes enriched, highlighting the intricate ballet of forces and materials that have shaped our planet. This critical investigation into the mechanisms and timing of carbonaceous chondrite delivery not only reshapes our perspective on planetary formation but also ignites curiosity about the ingredients that make up Earth and, by extension, ourselves. What other cosmic surprises are awaiting discovery? Stay tuned for more revelations from the universe!