Question

Evolutionary trees provide relative scales of divergence. How can these be reconciled with real times?

a) by comparing the amount of sequence divergence.

b) by comparing proteins from convergent evolution.

c) by using fossil records when possible.

d) All of the above.

e) None of the above.

PLEASE EXPLAIN

Answer 1

Answer: c) by using fossil records when possible.

Estimation of the molecular rate require to calibrate the tree of life with known values. Most of the microfossils of eukaryotic origin are large and the very long back time period of these are microfossils ranging ∼3.2-billion-year-old. This is done by carbon dating, passing years the ratio of 14C/13C (carbon isotopes) varies with time. Using first order kinetics integrated laws we can back calculate the age of tree. But how this method of fossil calibrations are applied on a tree is extremely important thing on age estimates, it will reflects on the age of the deepest nodes of the eukaryotic tree by hundreds of millions of years. This method of calculation depends on Hard constraints (also called as hard bounds) treat calibration points as fixed and time intervals predicted to particular nodes on the tree.

For further interest you may look at

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.113.5490&rep=rep1&type=pdf

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