Evolutionary dating how accurate
The carbon-14 in a sample decays at a steady rate after it dies, and thus works like a clock.
It is assumed that the amount of radioactive carbon left in the sample indicates how old it is. It is based on several assumptions, one of which is false.
The accuracy of these methods depends on both an adequate underlying model and the appropriate implementation of fossil evidence as calibration points. The ages obtained for the major clades of grasses by different methods and genetic markers were compared with the known fossil record.
We explore the effect of these in Poaceae (grasses), a diverse plant lineage with a very limited fossil record, focusing particularly on dating the early divergences in the group. 2011), angiosperm-wide dating projects have inferred a very recent origin for this same clade, between 23 and 39 Ma (Bell et al. The influence of a divergent calibration point, represented here by the most recently published phytolith fossils (Prasad et al.
This problem can be circumvented by using markers that have lower rate variation, and we show that phylogenetic markers extracted from complete nuclear genomes can be a useful complement to the more commonly used plastid markers. In this study, we explore the effect of variation in rates of mutation, fossil placement, and model assumptions on divergence time estimation, with the goal of inferring the age of the grasses (Poaceae; monocots). The vast majority of grass species belongs to two large sister groups referred to as BEP and PACMAD clades (Grass Phylogeny Working Group II 2012). Dating analyses were first conducted on DNA regions from the plastid genome, which are the most frequently used in plant phylogenetics and are available for a large number of taxa (Soltis et al. We selected three genes that are variable enough to reconstruct relationships within lineages but are also sufficiently conserved to be compared among distantly related angiosperms (Grass Phylogeny Working Group II 2012).
However, estimates of divergence times remain strongly affected by different implementations of fossil calibration points. Investigation into the appropriateness of rate autocorrelation has been inconclusive, yielding contrasting results depending on the data sets and methods used (Drummond et al. This diverse and ecologically important plant lineage of more than 11,000 species includes the world's major crops, such as rice, wheat, and maize, and natural grasslands cover large regions of the world's terrestrial land surface (e.g. Previous dating analyses of Poaceae have typically included only a limited number of taxa outside the focal group (Vicentini et al. These three markers are coding regions of the genes for ribulose-1,5-bisphosphate carboxylase large subunit ().
So scientists made calibration charts to make up for the variation.
Do you honestly think that no one has done anything about it? By making thousands (if not millions) of these adjustments we get a very good idea of how old a piece of unknown material can be. The 2009 calibration set extends the ‘well calibrated range’ to 50,000 years using the varves in a Japanese lake. This is unlike the creationists which think it happened, but can’t be bothered to check.
For this method to work, the rate of production of carbon-14 in the atmosphere has to remain constant through time.
In truth, however, the amount of carbon-14 in the atmosphere varies with fluctuations in solar activity and Earth’s magnetic field, changes in atmospheric conditions and even the exploding of atomic bombs!
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Doesn’t that give accurate dates of “prehistoric” civilizations?