Actually, I’m not a layman, and I have some ideas.
The Proterozoic (2 billion years ago) is a time period that geologists affectionately call the ‘boring billion’. In those rock strata, we very often find biogenic stromatolites, crumpled accretionary structures produced by the accumulation of mineral waste products in microbial metabolism. In the wild, they look like lumpy rocks on coastlines and in lakes, with a thin biofilm on top. Think of them as the microbial forests through which the early eukaryotes would have foraged and hunted. These ecosystems are also exclusively shallow-water, since they require sunlight and water in copious supply.
As such, they would be wiped out by a ‘moderate’ gamma ray burst, since they don’t have the protection of deep oceans. In other words, there would be a specific moment at which accretion halted for every biogenic stromatolite at the same time. This would be followed, in geologic history, by a shortish period in which newly lithified sediments lacked a biological influence, as life clawed its way back from the deep oceans. Even if the biosphere that followed was indistinguishable from the previous incarnation (which itself seems unlikely), we’d be able to see an interruption.
We haven’t yet found evidence of such a hiatus in the Precambrian. It’s a big history, so it’s always possible that the evidence will come in later- but it’s worth pointing out that we have found interruptions of comparable magnitude, from different sources.
Actually, I’m not a layman, and I have some ideas.
The Proterozoic (2 billion years ago) is a time period that geologists affectionately call the ‘boring billion’. In those rock strata, we very often find biogenic stromatolites, crumpled accretionary structures produced by the accumulation of mineral waste products in microbial metabolism. In the wild, they look like lumpy rocks on coastlines and in lakes, with a thin biofilm on top. Think of them as the microbial forests through which the early eukaryotes would have foraged and hunted. These ecosystems are also exclusively shallow-water, since they require sunlight and water in copious supply.
As such, they would be wiped out by a ‘moderate’ gamma ray burst, since they don’t have the protection of deep oceans. In other words, there would be a specific moment at which accretion halted for every biogenic stromatolite at the same time. This would be followed, in geologic history, by a shortish period in which newly lithified sediments lacked a biological influence, as life clawed its way back from the deep oceans. Even if the biosphere that followed was indistinguishable from the previous incarnation (which itself seems unlikely), we’d be able to see an interruption.
We haven’t yet found evidence of such a hiatus in the Precambrian. It’s a big history, so it’s always possible that the evidence will come in later- but it’s worth pointing out that we have found interruptions of comparable magnitude, from different sources.