&quot;Like this&quot; refers to the proposal that there were large numbers of iron chemotrophic organisms in the Precambrian.<p>Some elements (like Carbon) are known to be essential elements in the metabolism of biological organisms. This is why we would expect elements like Al and U to never show isotopic ratios associated with biological activity. Fe is used in living things, but only rarely. (The human body is 0.0006% Fe by weight.) To propose a biological origin for massive iron deposits is so far outside of what we know about biochemistry that it is not a legitimate proposal as is. The outlandishness of these proposed organisms equates to a very poor hypothesis that is not rigorous enough to be legitimately considered yet.