Russian researchers say they have found new support for the idea that something fell out of the sky onto the northern hemisphere about 12,900 to 12,800 years ago, and that the evidence is a coloured band in the mud at the bottom of Lake Onega.
The band is called the pink horizon: a layer in the varved clays where the colour changes sharply, traceable across the whole of the lake. In it the team found high concentrations of iron-oxide particles, tens to hundreds of micrometres across. That, together with the fact that the horizon holds a distinct boundary everywhere in the lake, may point to material arriving from outside — cosmic dust, for example. Dmitry Subetto, dean of the geography faculty at the Herzen State Pedagogical University, presented the finding at a palaeolimnology conference in Apatity.
What is new is less the idea than the resolution. For this round the team used magnetic measurements at intervals of four to five millimetres, and came out with what they call a magnetic fingerprint of the horizon — something that can now be recognised and matched against sediment sections elsewhere in the region. The same work, Subetto said, traced the whole passage from the ice age to the present climate at a single site for the first time.
The lake it came out of was not the lake that is there now. Ancient Onega covered 33,000 square kilometres, three times the present area, held 900 cubic kilometres of water and ran to 300 metres deep. In one to two thousand years it took in about 52 cubic kilometres of sediment — more than 30 billion tonnes of dry matter — against ten cubic kilometres over the nine or ten thousand years of the warm epoch that followed, a difference the researchers put down to melting ice and erosion across the catchment. Телеканал Санкт-Петербург adds that microbial mats and biofilms were found in the pink horizon itself, which could have formed at depths beyond a hundred metres.
The three accounts are one announcement. РИА Новости, Интерфакс and Телеканал Санкт-Петербург all attribute it to the university's press service, and they differ mainly in how much of the release each kept. On one point they part: РИА says the impact could have caused abrupt cooling and stops there, while the other two put the cooling at about a thousand years.
Why it is on the board
Top of РИА Новости's most-read list when we collected. A one-lens entry: the Russian video lens held four clips this round and none was this.
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