for ever
they where invented in 1883
It is not clear what law of conservation you are talking about. There are several.
About 300 years.
49 years
61years
It started in 1823
50
They were invented in 1997 ! :)
Invented in 1959
since computers were invented
Mango juice was not invented. It has been enjoyed for as long as humans have eaten fruit.
The law of Conservation of Mass was invented by a French chemist Antoine-Laurent Lavoisier.