Critics suggest other possible explanations, however. Hundreds of organic compounds have been identified in it, including amino acids and compounds closer to the things organisms actually use. The authors note that certain bacteria manufacture broadly similar magnetite and iron sulfide crystals. Joseph Kirschvink , a biomineralogist at the California Institute of Technology, agrees that the mineral formations are intriguing. I don't know of anything else that can make crystals like that.
Shock remains unconvinced.
There are other ways to get those shapes. The final thread of evidence is the one that has drawn the sharpest attacks from skeptics. Many scientists are still unconvinced that such organisms ever existed on Earth, let alone anywhere else. There is also a real danger of an observer effect at work. McKay adds that he looked at a different meteorite as a control and saw no similar formations.