Could some extraterrestrials have green blood like Mr. Spock?
A favorite theme of science fiction is the diversity of pigmentation that might exist among extraterrestrials due to differences in the color of their blood. Mr. Spock Star Trek’ s Mr. Spock, for example, has a greenish tinge to his skin on account of being a green-blooded Vulcan. The variation in the color of the blood of terrestrial species is due to differences in the metallic component of the blood from one species to another. Human blood, like that of all mammals and birds, is red because of a cocktail of iron-containing pigments, including hemoglobins (red), myoglobins (red), chlorocruorins (green), and hemerythrins (violet). Horseshoe crabs and certain other organisms, on the other hand, have blood in which the oxygen-carrier is hemocyanin, a copper-containing pigment that is blue. Perhaps Mr. Spock has blood which is similar to that of the humble sea cucumbers which is yellow-green and based on vanadium.
