This week’s “sciencey” tourist picture comes from the Petrified Forest National Park in Arizona:
The petrified logs in the park (as well as many other local fossils) date from the Triassic period, some 200 million years ago. The now-preserved wood was washed into an ancient river system, and buried quickly and deep enough that oxygen was cut off, and decay almost eliminated. Over the ensuing millennia, minerals absorbed into the wood, replacing the organic material, and crystalizing into almost solid quartz. Since the organic material is primarily replaced with Si02 (a.k.a., silica), this variety of petrification is called silicification (or agatization). The colors in the preserved logs are produced by mineral impurities in the quartz.
As the Colorado Plateau rose, starting some 60 million years ago, the petrified logs were exposed — often cracking like glass rods in the process. Visit today and you’ll find the landscape strewn with these logs, many cracked at regular intervals as if they’d been sectioned with an ancient chainsaw.
As usual, click on the above picture to get to the Flickr version of this image — it’ll give you lots of options for resizing and otherwise manipulating the source photo.