Do you have any references for this 0.4% claim?
Because, first the math doesns’t compute (5% of 70% is more than 0.4%), and additionally most of EurAsia and also Northern Americas is explored, with large parts of South America and Africa explored as well.
PS: NOAA.gov claims more than 80% of the oceans is unexplored, so that would point at 15% of 70%.
PPS: Many parts of the Amazon are explored already as well, but left alone because of the presence of tribes.