What is Late Heavy Bombardment?
[[Image:Lunar cataclysm.jpg|thumb|right|Artist's impression of the moon during the Late Heavy Bombardment (lunar cataclysm) and today]] The '''Late Heavy Bombardment''' ('''LHB''') or '''lunar cataclysm''' happened about 4.1 to 3.8 [[billion]] years ago. During this time, a large number of impact craters formed on the [[Moon]]. By [[Inference (grammar)|inference]], the same thing happened on [[Earth]], [[Mercury (planet)|Mercury]], [[Venus]], and [[Mars]] as well.<ref>Fazekas, Andrew (March 24, 2015). Observe: Jupiter, Wrecking Ball of Early Solar System. National Geographic. Archived from the original on March 14, 2017.[https://web.archive.org/web/20170314171306/http://news.nationalgeographic.com/2015/03/150324-jupiter-super-earth-collisions-planets-astronomy-sky-watching/]</ref> The evidence for this event comes from the [[radiometric dating|dating]] of lunar [[Sample (statistics)|samples]]. This shows that most impact melt rocks formed at that time. Many [[hypotheses]] have been suggested to explain how [[asteroid]]al or [[comet]]ary material got into the inner [[solar system]], but no consensus yet exists.<ref>Simpson J.A.; Weiner E.S.C. 1989. Jupiter. ''Oxford English Dictionary''. Vol. 8 (2nd ed), Clarendon Press. ISBN 978-0-19-861220-9</ref> One popular theory is that the [[gas giant]] planets (or at least [[Jupiter]]) migrated in [[orbit]] at this time: see [[Grand tack hypothesis]]. This caused objects in the [[asteroid belt]] and/or [[Kuiper belt]] to be forced into orbits which reached the [[terrestrial planet]]s. Some think that the apparent clustering of impact melt ages near this time is an artifact of sampling.<ref name=taylor1>Taylor G. Jeffrey 2006. [http://www.psrd.hawaii.edu/Aug06/cataclysmDynamics.html Wandering gas giants and lunar bombardment]</ref><ref>{{Cite journal|last=Cohen B.A; Swindle T.D.|first=& Kring D.A|date=2000|title=Support for the Lunar cataclysm hypothesis from lunar meteorite impact melt ages|journal=Science|volume=290|issue=5497|pages=1754–1755|doi=10.1126/science.290