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Impact rates in the first 500 Myr of the solar system are critical to an understanding of lunar geological history, but they have been controversial. The widely accepted, post‐Apollo paradigm of early lunar impact cratering (about 1975–2014) proposed very low or negligible impact cratering in the period from accretion (>4.4 Ga) to ~4.0 Ga ago, followed by an ~170 million year long spike of cataclysmic cratering, during which most prominent multi‐ring impact basins formed at age ~3.9 Ga. More recent dynamical models suggest very early intense impact rates, declining throughout the period from accretion until an age of ~3.0 Ga. These models remove the basin‐forming spike. This shift has important consequences vis‐à‐vis megaregolith evolution and properties of rock samples that can be collected on the lunar surface today. We adopt the Morbidelli et al. (2018) "accretion tail" model of early intense bombardment, declining as a function of time. We find effects differing from the previous models: early crater saturation and supersaturation; disturbance of magma ocean solidification; deep early megaregolith; and erosive destruction of the earliest multi‐ring basins, their impact melts, and their ejecta blankets. Our results explain observations such as differences in numbers of early lunar impact melts versus numbers of early igneous crustal rocks, highland breccias containing impact melts as old as 4.35 Ga, absence of a 170 Myr long spike in impact melt ages at 3.9 Ga among lunar and asteroidal meteorites, and GRAIL observations of lunar crustal structure. [ABSTRACT FROM AUTHOR]

- Micrometeoroids with 100 and 200 μm size dominate the zodiacal cloud dust. Such samples can be studied as micrometeorites, after their passage through the Earth atmosphere, or as microxenoliths, i.e., submillimetric meteorite inclusions. Microxenoliths are samples of the zodiacal cloud dust present in the asteroid Main Belt hundreds of millions years ago. Carbonaceous microxenoliths represent the majority of observed microxenoliths. They have been studied in detail in howardites and H chondrites. We investigate the role of carbonaceous asteroids and Jupiter-family comets as carbonaceous microxenolith parent bodies. The probability of low velocity collisions of asteroidal and cometary micrometeoroids with selected asteroids is computed, starting from the micrometeoroid steady-state orbital distributions obtained by dynamical simulations. We selected possible parent bodies of howardites (Vesta) and H chondrites (Hebe, Flora, Eunomia, Koronis, Maria) as target asteroids. Estimates of the asteroidal and cometary micrometeoroid mass between 2 and 4 AU from the Sun are used to compute the micrometeoroid mass influx on each target. The results show that all the target asteroids (except Koronis) receive the same amount (within the uncertainties) of asteroidal and cometary micrometeoroids. Therefore, both these populations should be observed among howardite and H chondrite carbonaceous microxenoliths. However, this is not the case: carbonaceous microxenoliths show differences similar to those existing among different groups of carbonaceous chondrites (e.g., CI, CM, CR) but two sharply distinct populations are not observed. Our results and the observations can be reconciled assuming the existence of a continuum of mineralogical and chemical properties between carbonaceous asteroids and comets. [ABSTRACT FROM AUTHOR]