Stochastic accretion of the Earth.

Area of Science:

• Planetary Science
• Cosmochemistry
• Astrophysics

Background:

• Chondritic meteorites are traditionally considered Earth's building blocks.
• Earth exhibits unique volatile element depletion inconsistent with chondrites, despite retaining chondritic isotope ratios.

Purpose of the Study:

• To investigate the formation mechanism of Earth and explain its volatile depletion.
• To reconcile Earth's composition with models of planetary accretion.

Main Methods:

• Utilized N-body simulations to model planetary accretion.
• Incorporated variable precursor body compositions based on formation temperatures.
• Constrained disk accretion rates and the role of 26Al heating.

Main Results:

• Earth's composition is accurately reproduced by stochastic accretion of precursor bodies.
• Formation temperatures were dictated by disk accretion rates of (1.08±0.17)×10-7 solar masses/yr.
• 26Al heating can perturb compositions of bodies formed at different times.

Conclusions:

• Earth formed from diverse planetesimals and embryos, not solely chondrites.
• A heliocentric compositional gradient existed in the protoplanetary disk.
• Rapid planetesimal formation within ~1 Myr aligns with Earth's volatile depletion ages.