Deep Time

Another semester has started, which means back to the books for me.  But three weeks in, I'm pretty excited about the course I'm taking, the material I'll be learning, and the discussions I'll be a part of with my class and professor.  Last week we talked a little about deep time (in relation to some other topics I'm going to be covering in greater detail soon), and I realized how difficult of a concept it can be to wrap your head around, even for someone like myself who spends a great deal of time thinking about it.  I know the Earth is 4.54 ± 0.05 billion years old, but what does it mean when we all live in a timescale of years, hours, or even minutes? When most people think about time, this is probably not what comes to mind.

The GSA Geologic Time Scale, not actually to scale, from http://www.geosociety.org/science/timescale/timescl.pdf.

All those numbers and colors can be intimidating, so I find it's helpful to try and explain deep time to people in a way they can relate to.  Some use a 12 or 24 hour clock as an analogy.  Others use a calendar year.  I swear one time in ELT we used a role of receipt paper.  But my favorite analogy is one I always have on hand...

... GET IT!?!?

It's the human arm.  And it serves as a pretty good point of reference.  I'm not sure where I first learned it (probably from Merck and Holtz), but it goes a little something like this:

The Geologic Time Scale... kind of to scale... on my arm.

The start of the shoulder marks the formation of earth ~4.6 bya.  From there to the end of the shoulder/start of the arm is the length of the Hadean Eon.  The upper arm (4.0 bya to 2.5 bya) is the Archean Eon, terminating in the elbow.  From the elbow to the first knuckle of the middle finger (2.5 bya to 542 mya) is the Proterozoic, Eon and the Phanerozoic Eon starts there.  Breaking it down, the first knuckle to the second knuckle (542 to 252.2 mya) is the Paleozoic Era, and from the second knuckle to the cuticle (252.2 - 65.5 mya) is the Mesozoic Era. All that's left is the Cenozoic Era, which is basically your fingernail (65.5 mya to present).  And all of human existence is basically right there at the very tip. Years, hours, and minutes are small potatoes compared to the timespans we're talking about here.  But as the semester really starts to pick up speed, I still find myself wishing I had more of them!  Good old Deep Time sure puts things in perspective.