Lichen as a dating tool

30-Jan-2018 00:28 by 2 Comments

Lichen as a dating tool - online dating best membership russian good

This is to determine if the size of the lichen varies across the moraine and to identify any influencing factors which may be contributing to a size variation.

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However, researchers have found a 'Green Zone' and the hypothesis suggests that lichens are larger at the proximal (side of the moraine closest to the glacier) base of terminal moraines (ridge of sediment that is deposited when a glacier retreats) than at other locations (Haines-Young, 1983).

As a result lichens which colonize the recently exposed rock would not reflect the true age of the moraine.

It has been suggested by Armstrong (2002) that the aspect of rock surfaces may affect the growth of the lichen ; his results from Gwynedd, North Wales, showed that the radial growth of the thalli on the north-west facing slopes was 'significantly greater' than that on the south-east facing slopes (Armstrong, 2002: 193).

Lichenometric dating curves have been produced by numerous researchers (Bickerton and Matthews, 1992; Erikstad and Sollid, 1986; Mottershead and White, 1972) and relate the size of the largest lichens in a population to a surface of known age (Loso and Doak, 2006) to enable a surface of unknown age to be approximately dated.

These dates can vary, however, some by 28 years and others by 15-25 years (Matthews, 1994), which highlights the inaccuracy of the technique.

If lichens are to be used successfully as a dating tool then the factors which hinder or promote growth need to be understood or data may be unreliable.

Lichenometry is a dating technique which fairly accurately identifies the age of a deposited surface by measuring the thalli of lichens, which are a symbiosis of two organisms, fungi and algae (Armstrong, 2004).

The lichen growth curves, and also the dating curves to some extent, assume that the environmental conditions have remained the same through time without fluctuation.

Some research has been completed to understand the influence of water (Gregory, 1976; Andrews and Webber, 1964; Curry, 1969 and Harvey , 1984), snow patches (Carroll, 1974 and Benedict, 1993) and aspect (Armstrong, 2002) on the growth of lichens, but this is only a small number.

This hypothesis is tested by data which was collected from six dated moraines on the glacial foreland of Nigardsbreen in the Jostedal, Norway.

Five transects were taken across each moraine, each consisting of 3 metre x 3 metre quadrats where the five largest lichens were measured (Innes, 1984: 343).

This could be anomalous; however, if the 'Green Zone' does exist there are implications for the reliability of previous studies as they could conclude that substrates are older because the lichen sizes are larger.