It really is hard to fathom the scale of geologic time. The recent TV series “Cosmos” used one favorite trick, compressing the history of the universe into a single calendar year. This graphic is a different setup, showing the age of the Earth on the face of a clock.
If we tried to picture how long our lives are on a geologic timeline, the bit of the planet’s history that we occupy barely registers. The Earth is right around 4.56 billion years old. If that length of time were compressed into 12 hours, then each second on the clock face would represent over 100,000 years.
1 second ago on this clock face was during the start of the last glaciation. During that last second, 90,000 years of glaciation and the rise of the entire human civilization took place.
Many of the major events in evolution are shown on this clock. The appearances of land plants, land animals, animals in the oceans with hard parts, and multicellular life all are shown. There Yesterday, we referred to an era of time in the Precambrian covering nearly a billion years; that is ¼ of this clock. Even geologists are used to thinking of time periods like the Cambrian as a long time ago, but the last 540 million years is but 10% of this clock, equivalent to an hour and 20 minutes.
Some quibbles could be taken with exactly where the dates are hung on this clock, but the mental exercise of comparing all of human civilization taking place in a tenth of a second is hopefully an interesting way to think about geologic time.
Image credit: (public domain label):http://en.wikipedia.org/?title=Talk%3AGeologic_Timescale#mediaviewer/File:Geologic_clock.jpg