Collisions and impact processes have been important throughout the history of the solar system, including that of the Earth. Small bodies in the early solar system, the planetesimals, grew through collisions, ultimately forming the planets. The Earth started growing ca. 4.56 Ga in this way. Its early history was dominated by violent impacts and collisions, of which we only have circumstantial evidence. The Earth was still growing and had reached ∼70%–80% of its present mass when at ca. 4.5 Ga a Mars-sized protoplanet collided with Earth, leading to the formation of the moon—at least according to the currently most popular hypothesis of lunar origin. After its formation, the moon was subjected to intense post-accretionary bombardment between ca. 4.5 and 3.9 Ga. In addition, there is convincing evidence that the Moon experienced an interval of intense bombardment with a maximum at ca. 3.85 ± 0.05 Ga; subsequent mare plains as old as 3.7 or 3.8 Ga are preserved. It is evident that if a late heavy bombardment occurred on the Moon, the Earth must have been subjected to an impact flux at least as intense as that recorded on the Moon. The consequences for the Earth must have been devastating, although the exact consequences are the subject of debate (total remelting of the crust versus minimal effects on possibly emerging life forms). So far, no unequivocal record of a late heavy bombardment on the early Earth has been found. The earliest rocks on Earth date back to slightly after the end of the heavy bombardment, although there are relict zircons that have ages of up to 4.4 Ga (in which, however, no impact-characteristic shock features were found so far). In terms of evidence for impact on Earth, the first solid evidence exists in the form of various spherule layers found in South Africa and Australia with ages between ca. 3.4 and 2.5 Ga; these layers represent several (the exact number is still unknown) large-scale impact events. The oldest documented (and preserved) impact craters on Earth have ages of 2.02 and 1.86 Ga. Thus, the impact record for more than half of the geological history of the Earth is incomplete and not well preserved, and we mostly have only indirect evidence regarding the impact record and its effects during the first 2.5 b.y. of Earth history.

A new method to determine organic and inorganic associations of trace elements in coal was devised using the ratio of concentrations for 34 elements in five vitrinite concentrates to the concentrations in companion whole-coal samples. Trace-element concentrations were determined by instrumental neutron activation analysis. The samples, all high volatile A (hvA) bituminous coal, were from five different coal beds: two from the Appalachian basin, West Virginia and Alabama, USA; two from the Pennine coalfield, England; and one from the Sydney Basin, Australia. The ash content (weight percent) of the vitrinite concentrates after combustion at 960 to 1,000 °C ranged from 0.6 to 1.3 percent, as compared to 2.5 to 7 percent in the whole coals. Most of the trace elements are enriched in the whole coal relative to the vitrinite concentrates, with some notable exceptions: (1) in the Australian coal, 12 of the 22 elements detected in both the whole-coal and the vitrinite concentrates are enriched in the vitrinite concentrates; (2) arsenic is enriched by 1.2 to 2.2 times in the concentrates in four of five coals; in the remaining coal, from West Virginia, arsenic is enriched in the whole coal by a factor of 22, and the iron is also enriched by a similar factor, which indicate that arsenic is associated with pyrite in this sample; (3) antimony is enriched in the vitrinite concentrates of the three foreign coal samples; (4) tungsten is enriched in the vitrinite concentrates of the four samples where tungsten was detected in both the concentrate and the whole coal; (5) the ash- and shale-normalized rare-earth element (REE) patterns suggest that some of the organic matter is enriched in REE.