Calibration of phylogenic trees with respect to time since divergence is based on:

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Calibration of phylogenic trees with respect to time since divergence is primarily based on fossil and/or geological records. These records provide the most direct evidence of when species diverged and can be used to estimate the rate of molecular evolution in different lineages. While methods based on molecular data (such as mutation frequency and "housekeeping" genes) can be used to infer evolutionary relationships and divergence times, they require calibration against a known timescale, which is often provided by fossil data. The number of nodes and branches and whether the tree is rooted or unrooted are important considerations for inferring evolutionary relationships but are not directly related to the calibration of the timescale.

Calibration of Phylogenic Trees with Respect to Time Since Divergence