Pakistan, April 22 -- A NASA rover has discovered more building blocks of life on Mars after carrying out a chemistry experiment never before conducted on another planet, scientists said Tuesday.

The organic molecules are not definitive evidence of past life, the NASA-led team emphasised, because they could also have formed on the red planet or crash-landed on meteorites.

But it proves that these important clues to Martian history have been preserved on the surface for more than three billion years, they added.

Back then, the surface of Mars was thought to have been dotted with huge lakes and rivers full of liquid water, a key ingredient for life as we know it.

NASA's Curiosity rover landed in a former lake bed called the Gale crater ...