Who's got big balls?

Detailed studies (i.e., Boles et al., 1985; Thyne and Boles, 1989; Scotchman, 1991; Mozley and Burns, 1993; McBride et al., 2003; Chan et al., 2005; Mozley and Davis, 2005) published in peer-reviewed journals have demonstrated that concretions form [in sedimentary depositional environments] subsequent to burial during diagenesis. They quite often form by the precipitation of a considerable amount of cementing material [usually calcium carbonate] around a nucleus, often organic, such as a leaf, tooth, piece of shell or fossil. For this reason, fossil collectors commonly break open concretions in their search for fossil animal and plant specimens. Some of the most unusual concretion nuclei, as documented by Al-Agha et al. (1995), are World War II military shells, bombs, and shrapnel, which are found inside siderite concretions found in an English coastal salt marsh.

Attention is often given to oxygen since it is not only vital to the respiration of most life on the planet, but it also provides protection, via the ozone layer, from the harsh UV radiation generated by the Sun. Most scientists now recognise that the atmosphere of the early Earth was nearly devoid of oxygen and that during two main events the amount of oxygen rose in substantial amounts. The first of these events occurred approximately 2.3 billion years ago (Ga) and is now referred to as the Great Oxidation Event (GOE). The second occurred roughly 600-500 million years ago (Ma) and paved the way for the evolution of life. The presence of atmospheric oxygen requires oxygenic photosynthesis, a process performed predominantly by cyanobacteria, and a steady-state of oxygen consumption that doesn’t exceed its production. Detecting the presence of an oxygenated atmosphere, therefore, provides clues regarding the evolution of life and the transition to an Earth habitable by complex multicellular life. But, how do scientists detect the presence or absence of oxygen in the atmosphere millions and even billions of years ago?