Evolution on other planets could have taken a different direction, with dinosaurs dominating over mammals, researcher Ronald Breslow says.
Breslow, a chemist, has studied the mystery of why the building blocks of terrestrial amino acids, sugars, and the genetic materials DNA and RNA exist mainly in one orientation or shape.
There are two possible orientations, left and right, which mirror each other in the same way as hands do.
With the exception of a few bacteria, amino acids in all life on Earth have the left-handed L orientation while most sugars have a right-handed D orientation.
Writing in the Journal of the American Chemical Society, Breslow suggests unusual amino acids carried to a lifeless Earth by meteorites about 4 billion years ago set the pattern for amino acids and sugars on Earth, but says it could have been different on planets in far-off solar systems.
"An implication from this work is that elsewhere in the universe there could be life forms based on D-amino acids and L-sugars. Such life forms could well be advanced versions of dinosaurs, if mammals did not have the good fortune to have the dinosaurs wiped out by an asteroidal collision, as on Earth.
"We would be better off not meeting them," he said.