Christianity had a hard time in its first four centuries as a faith, especially at the centre of the Roman Empire. Persecution of Christians ended abruptly with the conversion of Emperor Constantine in 312 AD. Legend has it that, while faced with the double problem of northern barbarian hordes at the gates of Rome and dissident Christians within, Constantine saw a vision in the sky while preparing to take on the invaders. Immediately converting to Christianity, he saw off the hordes, albeit temporarily, and the rest, as they say, is history. One version of the legend, from the Sirente region of Central Italy, tells of a new star that came nearer and nearer to disappear behind the mountains, with a blaze of light from horizon to horizon and ground shaking. Unsurprisingly, impact theorists latched onto this because of its similarity to what probably happens when a substantial meteorite strikes the Earth. Geologists from Sweden have discovered a small crater field in the Sirente area, that consists of a 125 m wide, circular lake with a raised and deformed lip, and several lesser craters dotted around it. Preliminary dating gives an age of 412+ 40 years. Although this date is a century later than Constantine’s conversion, contamination with later material might have reduced the actual age. If the link does prove to be substantial, the Sirente impact will rank with other catastrophes that literally made history, such as the filling of the Black Sea which has been argued to be the inspiration for the Biblical Flood and the Epic of Gilgamesh, and the explosive volcanism of Santorini that wiped out Minoan civilisation on Crete and may well be recorded apocryphally in the Old Testament.
Source: Chandler, D.L. 2003. Crater find backs falling star legend. New Scientist, 21 June 2003, p. 13.
Middle Devonian extinction and impactite layer
Around 380 Ma there was a major extinction event (~40% of marine animals) that is recorded world-wide, along with negative shifts in 13C. As with other extinctions since the discovery that the Chixculub crater was exactly the same age as the famous K/T extinction, there has been a quest to link this Middle Devonian event to an extraterrestrial cause. Now there seems to be a positive result (Ellwood, B.B. and 4 others 2003. Impact eject layer from the mid-Devonian: possible connection to global mass extinctions. Science, v. 300, p. 1734-1737). A Devonian section in Morocco contains a thin layer rich in shocked quartz, microspherules of devitrified glass, and metals, that also has low d13C. The carbon-isotope shift could have resulted from either of two possible consequences: collapse of the marine ecosystem; or massive release of methane from gas hydrates destabilised by the impact. Only one crater coincides wit the date of the layer and the extinction, Kaluga in Russia, but it is only 15 km wide, so cannot have had any dramatic biological effect. However, the very presence of a moderate crater at exactly the right age might signify other impacts, because it is becoming increasing clear that impacts come in clusters, perhaps because large, approaching bodies break up before they hit the Earth.