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This Date in the Earth Year September 14, 2009

Proterozoic life (Image used by permission of A.H. Knoll)

Earth formed approximately 4.5 billion years ago (bya) also known as 4500 million years ago. It’s difficult, maybe even impossible to get a good sense of this length of time. Yet we must “feel deep time in our guts” as my late-mentor Steve Gould referred to the endeavor, if we are to live harmoniously on the planet. Today I write the first of an occasional series, “This Date in the Earth Year,” in an effort to help the layperson develop a feel for geologic (deep) time.

Using a calendar year as a metaphor for the 4500 million years of Earth history and employing January 1, New Year’s Day, as the Earth’s birthday, I calculate the current date’s location in the Earth Year and detail what was happening paleontologically at that moment in Earth history. For example today, September 14, is day 257 out of 365 days in this (non-leap) year. With so much of a calendar year having elapsed, one might think that at this point in the Earth Year, some pretty complex organisms might have been roaming the planet. Not so.

In geologic time, September 14 represents 1330 million years ago, the Proterozoic —the second of two eons that comprise the immense stretch of time called the Precambrian. Many of the most important events in earth history took place during the Precambrian including the formation of life, the accretion of the earth’s first tectonic plates, the proliferation of oxygen in the atmosphere, and the evolution of eukaryotic cells (single-celled organisms with internal organization). Still, at 1330 million years—the middle Proterozoic—the only living things on Earth were ocean-dwelling single-celled organisms.