What did Lord Kelvin use to deduce the age of the Earth?

Lord Kelvin was a highly respected physicist. So much so that his ideas of the Earth’s age persisted for over 100 years after his death. His irrefutable mathematical calculations were based on

A. the recently established half-life of U238.  Using this information he determined the Earth’s absolute age by sampling rocks from around the planet. The Earth’s age was as old as the oldest sample.

B. the discovery of set of sedimentary layers of the Nile River in Egypt. These layers were put down year after year since the Earth formed. A simple counting of the layers was all that was needed to determine the Earth’s age.

C. the fact that Earth began as a molten sphere. With this fact he was able to use simple physics laws to determine how long it took for the planet to cool to its present temperature.

D. the salinity of the oceans. It was known that the oceans began as fresh water bodies. With erosion of the landmasses, salt was transported to the oceans to create its salinity. Calculating the average rainfall each year for all of the continents and estimating the flow of water to the oceans each year, and knowing (by field research) the salinity of the major rivers flowing into the ocean, he was able to accurately determine Earth’s age.