Editing Hadean Eon (section)

== The Late Heavy Bombardment ==
The Late Heavy Bombardment (LHB) is a proposed period in the Solar System's history characterized by an intense increase in the rate of asteroid and comet impacts on the inner planets. This event is thought to have occurred approximately 4.1 to 3.8 billion years ago, during the tail end of the Hadean Eon and into the early [[Archean Eon]]. The prevailing theory suggests that gravitational perturbations in the outer Solar System, caused by the migration of the gas giants (Jupiter and Saturn), destabilized distant asteroid and comet orbits. This led to a significant increase in objects being sent into the inner Solar System, where they collided with the terrestrial planets.

The '''Grand Tack Hypothesis''' and the '''Nice model''' are two prominent theories explaining these gravitational perturbations. The Grand Tack Hypothesis proposes that Jupiter migrated inward before being pulled back outward by Saturn, scattering objects toward the inner Solar System. The Nice model suggests that interactions among the gas giants, and with a primordial disk of planetesimals, led to the rearrangement of the outer planets and a subsequent influx of comets and asteroids into the inner Solar System.

Regardless of the catalyst for movement, the majority of impacts during the LHB were likely caused by asteroids dislodged from the main asteroid belt. These impacts ranged from small craters to massive basins hundreds of kilometers in diameter. Comets, originating from the Kuiper Belt and Oort Cloud, also contributed to the LHB. While less frequent, cometary impacts would have delivered significant amounts of water and organic materials to the terrestrial planets. 

The Moon's heavily cratered highlands provide the most direct evidence of the LHB. Lunar samples returned by the Apollo missions have been dated to this period, supporting the hypothesis. The Moon's lack of geological activity has preserved these impact craters, serving as a record of this tumultuous time. The LHB likely played a significant role in shaping Earth's surface, though evidence of specific impacts has been largely erased by active plate tectonics and erosion. The delivery of water and organic molecules via cometary impacts may have been crucial for the development of life. Mars shows evidence of massive impact basins dating back to the LHB period, such as the Hellas and Argyre basins. Mars' thinner atmosphere compared to Earth's would have offered less protection against impacts, leading to significant surface modification. Like the Moon, Mercury's surface preserves a record of intense cratering from this period. Its global magnetic field may have been affected by large impacts, which could have contributed to the planet's high iron content.

The high frequency of impacts during the LHB led to extensive resurfacing of the terrestrial planets, erasing much of the earlier geological record. Impacts would have had significant effects on the planets' atmospheres, potentially stripping away or adding gases. On Earth, this could have influenced the early climate and the conditions necessary for life to emerge. The LHB is thought to have played a crucial role in delivering water and organic molecules to the inner planets, particularly Earth, potentially seeding the conditions necessary for life.

Some theories suggest that the LHB was a consequence of the Moon's formation, with the destabilization of asteroid orbits resulting from gravitational effects of the newly formed Earth-Moon system.

=== Duration and Timing ===
The LHB is believed to have lasted approximately 300 million years, starting around 4.1 billion years ago and tapering off by about 3.8 billion years ago. This period corresponds with the end of planetary formation and the beginning of a more stable phase in Solar System history. The Late Heavy Bombardment represents a formative period in the Solar System's development, profoundly affecting the terrestrial planets' geological and potentially biological evolution. The exact causes, timing, and effects of the LHB continue to be subjects of active research and debate within the planetary science community.
[[Category:Physics]]
[[Category:Astronomy]]
[[Category:Chemistry]]
[[Category:Quantum Physics]]
[[Category:Hadean Eon]]