  In this paper we conduct a longitudinal analysis of the structure of labour
markets in the US over 7 decades of technological, economic and policy change.
We make use of network science, natural language processing and machine
learning to uncover structural changes in the labour market over time. We find
a steady rate of both disappearance of jobs and a shift in the required work
tasks, despite much technological and economic change over this time period.
Machine learning is used to classify jobs as being predominantly cognitive or
physical based on the textual description of the workplace tasks. We also
measure increasing polarisation between these two classes of jobs, linked by
the similarity of tasks, over time that could constrain workers wishing to move
to different jobs.
