1.1: Stories from stone

What stories has the Earth written in the language of Rock? Consider this cobble, found in Montana:

Figure \(\PageIndex{1}\): What is the history of a rock like this? What did it take for this thing to exist? (Callan Bentley photo.)

This chunk of rock contains features that we can translate into information. The variety of materials it is made from, how those materials are arranged, other features that cut across them, and the shape of the sample all convey information about past processes and circumstances. What would it take to make a rock just like this one? Why does it exist in this particular way?

As an exercise in practicing decoding Rock, let’s translate: The smooth tan material is limestone. It originally formed as inorganic deposits of carbonate mud, laid down (1) in calm water, as evidenced from its very fine grain size. It sat still long enough to stick together into a semi-coherent mass. But then it must have been savagely ripped up to make (2) mud-chip clasts & entombed in (3) quartz sand. The event that was energetic enough to tear into the carbonate mud and rip it up, as well as energetic enough to transport in coarse particles of sand. It must have been a storm, perhaps a hurricane. The threat of more violent storms diminished as the sediment was buried and sank further and further underground, smothered beneath the crushing weight of thousands of feet of sediment piled atop it. Then the carbonate mud chunks and surrounding quartz sand (4) lithified into rock: No longer loose sediment, it was transformed through compaction and cementation into solid, coherent rock: limestone clasts in quartz sandstone. After it was solid rock, it broke. Some stress, perhaps imparted by the wrenching compression of mountain building, snapped the bonds holding the rock together. This made fractures, but those fractures were soon healed by the precipitation of the mineral quartz, making (5) thin quartz veins. This is something that must have taken place deep underground, but in order for us to pick it up and hold it, we know it must thereafter have been (6) uplifted. It made its way back to Earth’s surface, and this particular chunk was broken off from its source outcrop. Finally, it experienced (7) differential weathering, etching away the limestone more readily than the quartz sandstone. This gives the sample its distinctive texture.

The rock is no longer just a rock. By speaking its language, we have turned it into a book, with seven chapters.

Figure \(\PageIndex{2}\): Points of annotation showing the 7-chapter history of this one rock sample. (Callan Bentley photo.)

This is the power of Historical Geology: it allows curious humans to interact with inert rock, and coax stories from that rock — vital tales of the planet’s ancient past. Being able to decode the stories of rocks, hidden in plain sight, is an ability akin to an acquired superpower. As Spiderman gained his powers after being bitten by a radioactive spider, you are about to be bitten by the Historical Geology bug. What you learn will change the way you look at your world.

Like the best stories from our favorite storytellers, what we learn resonates with us, changes us. The Earth’s many tales help us understand our present, live our lives more meaningfully, and prepare for a future we can better comprehend. The perspective granted by speaking Rock helps us live better lives, and look to the future with hope and confidence.