Conversation so far:
where do the prime meridian and the international date line meet
The prime meridian separates the eastern hemisphere from the western hemisphere. Halfway around the world, at 180 degrees longitude, is the International Date Line
what is the offical prime meridian
There is an international agreement that the meridian that runs through Greenwich, England, is considered the official prime meridian.
when was the official prime meridian chosen
At an international convention called by U.S. President Chester Arthur in 1884, representatives from 25 countries agreed to make the Greenwich Meridian the international standard for the prime meridian.

Question: what is the modern line
Self-contained rewrite: what is the modern prime meridian