Free Astronomy Magazine May-June 2018

43 MAY-JUNE 2018 ASTROBIOLOGY Let’s see how Schmidt and Frank address these issues in the IJA article: “Since the mid-18 th Century, humans have released over 0.5 trillion tons of fossil carbon via the burning of coal, oil and natural gas (Le Quéré et al., 2016), at a rate orders of mag- nitude faster than natural long-term sources or sinks. In addition, there has been wide- spread deforestation and addition of car- bon dioxide into the air via biomass burn- ing. All of this carbon is biological in origin and is thus depleted in 13 C compared to the much larger pool of inorganic carbon (Rev- elle & Suess, 1957). Thus the ratio of 13 C to 12 C in the atmosphere, ocean and soils is de- creasing with a current change of around - 1‰ δ 13 C since the pre-industrial (Böhm et al., 2002; Eide et al., 2017) in the surface ocean and atmosphere” . If all this had already happened in a very distant past, the sedimentary layers of that era should retain its traces. But the sedi- ments could be so altered with respect to the previous and following ones as to be- come themselves evidence. Deforestation and global warming are also the cause of significant soil erosion, either directly, for the felling of trees, or indirectly, for the increase in rainfall due to the greenhouse effect. The eroded soil usually ends up de- positing in coastal regions, and a higher stratum per unit of time, with different properties, could indicate an unnatural al- teration of the climate. Here’s how Schmidt and Frank elaborate on this point: “In ad- dition to changes in the flux of sediment from land to ocean, the composition of the sediment will also change. Due to the in- creased dissolution of CO 2 in the ocean as a function of anthropogenic CO 2 emissions, the upper ocean is acidifying (a 26% in- crease in H+ or 0.1 pH decrease since the 19th Century) (Orr et al., 2005). […] As dis- cussed above, nitrogen load in rivers is in- creasing as a function of agricultural prac- tices. This in turn is leading to more micro- T his spherical concretion, unearthed in Bosnia a few years ago, could suggest the dis- covery of an arti- fact created by an unknown civiliza- tion. Instead, it is a natural, and not all that rare, geo- logical formation. [Dado Ruvic/Reu- ters/Newscom]