Without oxygen connected, blood is a darker red color. Carbon monoxide, a potentially deadly gas, can also bind to heme, with a bond around 200 times stronger than that of oxygen.

Under high pressure, oxygen molecules (labeled O1-O2 and O3-O3) aggregate into groups of four, each of which is surrounded by four neighbors. Such a grouping of molecules had never been observed.

In 1979, chemists discovered that, at pressures above 10 GPa, oxygen becomes a red solid 1. At 96 GPa, oxygen molecules are so close that electrons flow freely between them, in a metallic phase ...