From Dave Smith, Alnwick, Northumberland, UK
Instead of using a 1950s sedimentary layer in a lake in Canada to define the start of the Anthropocene, I suggest that the appearance of lead in Greenland ice is, at least, a measurable and significant marker of our activity.
Lead levels in Greenland ice became significant from 1000 BC, but they skyrocketed when leaded fuel was introduced and became widely used in the 20th century.
