A view of non‐analog worlds

I’ll readily admit that I had promised to finish this book review before the beginning of the current academic year, having read it earlier this summer during our first field season. But, somehow the northern hemisphere summer has passed quickly and the leaves are now beginning to turn color in the northeast; it’s only mid-September. Our concept of time goes back towards the dawn of civilization when early societies used a variety of astronomical means to track the seasons. The earliest Assyrian calendar was based on the lunar cycle, but such a means of keeping time necessitated the introduction of additional months in leap years to even things out. And, even though the early Romans tried to standardize their concepts of time defining months as having either 29 or 31 days (30 was an unlucky number then), the addition of an extra month every second year (i.e., Mercedonius) was necessary. In 45 BC, Caesar reformed the calendar which became known as the Julian calendar, comprised of months of either 30 or 31 days and a leap year. But, under this scheme, the date of the vernal equinox drifted. It wasn’t until the Council of Trent (1545–1563) when Pope Gregory XIII authorized the reformation of the calendar that the Gregorian Calendar was conceived and adopted where every fourth year became a leap year (except for century years not divisible by 400). Even then, the Gregorian calendar wasn’t universally adopted until 1918 when the Russians changed from their long-held Julian calendar. Why spend so much time talking about time and our concepts of time? Why not just get to the book review? Since the discovery of radioactivity by Becquerel and the Curies and the development of geochronological techniques within the last 100 yr, geoscientists have recognized that time is as immense as the concept of the universe is to physicists. This concept of Deep Time has radically changed the way in which we view our planet and the timing of the abiotic and biotic processes involved in its evolution. The first radioisotopic scale was published in 1934, and advances in the identification and proof of a variety of decay series allowed for independent mineralogical assemblages from the same rock to be assessed, thereby confirming the numerical age of crystallization. It is this fact, that Earth has a very very long, almost incomprehensible, historical record, that Andy Knoll has outlined elegantly in Life on a Young Planet. We are grounded in the life and times that surround us; but we are asked in this book to abandon our perspectives and concepts of the time governing our lives to consider evidence and processes operating on scales without personal reference. The challenge is rewarding. Andy Knoll is Fisher Professor of Natural History at Harvard University where he studied with Elso Barghoorn at Pre-