In nature from 28/10/2010 U.S. researchers report the development of the concentration of phosphorus over a period of 3-4 billion years (Planavsky NJ, Rouxel OJ, Bekker A, Lalonde SV, Konhauser KO, Reinhard CT, & Lyons TW (2010). The evolution of the marine phosphate reservoir. Nature, 467 (7319), 1088-90 PMID: 20981096). They found that there were, 700 million years ago, particularly high phosphorus concentrations.
Why is this newsworthy? First because at this time the the global glaciation decreased (Snowball Earth), and because the concentration of oxygen in the atmosphere increased considerably, which should have led to a strengthening of the ozone layer. Consequently, it came to the spread of animal life on Earth, and this process is ultimately quite important for us humans.
But why did the oxygen concentration in the air increase? That is the burning question, the authors have found for perhaps an explanation. They suspect that it might be just come by the decline of the ice to an increased input of phosphorus into the sea. This led into a kind of algae bloom and with the death of these algae fresh oxygen came into in the ocean and atmosphere.
So far, so plausible. Interesting for me is above all, how the authors brought together theory, empirical analysis and experiment into a plausible hypothesis. In fact, also the experiment plays a role, because the concentration of phosphorus in the ocean water must be determined from the characteristic iron-phosphorus ratio in the sediment, and how the turn from the phosphorus content of the water depends, one can determine in laboratory experiments (even if the transfer of results to the primordial ocean billions of years ago seems very uncertain).
In addition to the current experiment, we have the experience of the mechanism of action of algal blooms, this hypothetical approach is also transmitted to the time of Snowball Earth. In addition, the measurement of phosphate concentrations in rock drilling, plus age determinations of individual samples.
All this is put together into a coherent picture from which we gain an idea of what could have been at that time 700 million years ago. Maybe it was different, perhaps some of the many assumptions of the authors are wrong. This will be discussed, perhaps it is plausible to other researchers , perhaps they will find other puzzle pieces that support the thesis of this article, perhaps they will be discarded. This creates something we call, for a time, the truth about our past, a truth which we need because we want to know where we come from.