What is the international date line? describe its geographic location. why doesn't it follow a straight line? why do we need it?

The International Date Line (IDL) is a line that separates the world into two hemispheres. It was first established in 1884 during the International Meridian Conference which was attended by 26 countries. It is located at the 180° longitude, which is the east of Greenwich, United Kingdom. 

The International Date Line does not follow a straight line because it has to avoid countries or groups of islands. The main purpose of the zigzag pattern of the IDL is to avoid confusion regarding time.

The IDL is important because it's the basis for our time zones. Back in the nineteenth century, scientists as well other professionals in various industries proposed to adopt the 24 time zone system which centered on the IDL's principle of adopting the proper "time". The IDL divides the world into two dates: the East of the IDL is a day behind compared to the West of the IDL. 

Answer collision and mountain formation;

Ascenario that doesnt  include any modern objects like electricity