Welcome to Day 28 of 31 Days of A Sense of Place.

*

“All things pass. None of us can manage to hold on to anything. In that way, we live our lives.” — Haruki Murakami, from Hear the Wind Sing

*

In terms of Earth’s history, we are fleeting.

It all started in Hadean time, 4600 to 4000 million (4.6 to 4 billion) years ago, when the solar system was forming. The oldest meteorites and lunar rocks are about 4.5 billion years old. The Earth was molten until it cooled, around 3.8 billion years ago.

During the Archean era, which lasted about 1.5 billion years (4000 to 2500 million years ago, or 4 to 2.5 billion years ago), Earth’s atmosphere was mainly methane, ammonia, and other toxic (to our life) gases. The Earth’s crust cooled during this time, with rocks and continental plates forming, and life in the form of bacteria first appeared.

Then, just 2.5 billion years ago to 542 million years ago, came the Proterozoic era, when stable continents first appeared, bacteria and other microorganisms flourished (and some algaes, about a billion years ago), and oxygen began to increase in the atmosphere, killing off some organisms while beginning to make the planet habitable for others.

Next, the very exciting Paleozoic era (542 to 251 million years ago), which began when multi-celled animals became much more diverse, leading to the creation of almost all animal phyla (and animals including fish, the first air-breathers, sharks, amphibians, reptiles, spiders, cockroaches, scorpions), and which ended with a mass extinction that destroyed about 90% of all marine animal species. The Earth comprised six major continental land masses, but they weren’t in the same configuration as our current continents. Limestone and coal were formed during this period as the Earth shifted to and fro.

From 251 million to 65.5 million years ago, dinosaurs roamed the planet in the Mesozoic era (which includes the Jurassic period), but by the end of the era, all dinosaurs except the birds had become extinct. Plant life moved from ferns, cycads, ginkgophytes, etc., to modern gymnosperms, like conifers, and then flowering plants and deciduous trees came along.

Finally, the era we’re in now, the Cenozoic, began 65.5 million years ago. A diversity of mammals, birds, insects, flowering plants abound, and along about 6 million years ago, our ape ancestors came into being. Two million years ago the first animals classified in the genus Homo appeared, but the modern form of humans evolved only about 200,000 years ago, and “civilization” is only about 6,000 years ago.

(For more on geologic time, check out the Univ. of California’s Museum of Paleontology timeline. InfoPlease also has a good chart.)

*

Another way to look at it: If geologic time were condensed into one year, with the Earth forming on 1 January, bacteria and some algae came along in early April, the first land plants around mid-July, in August fish and amphibians, in Sept. insects and, by the end of the month, dinosaurs. In October, dinosaurs and the first mammals. By December, more mammals, and by Christmas, the Grand Canyon would be formed by the Colorado River. No humans at sunrise on 31 Dec. but by noon, the first hominids and later in the day, massive ice sheets would cover America and Euroasia. An hour before the new year, Neanderthals show up, and at 11:55 p.m., civilization begins. (With thanks to WanderLearn)

*

I mention all this only to say that all things pass, and much has passed, long before any human was here to notice, admire, or engineer.

The rocks we see every day, all around us, are one connection to our very distant past, one way to know our place on this planet. There are igneous rocks (granite,  scoria, pumice, basalt, obsidian), the most plentiful on our planet, that are formed from lava flows and from magma inside the Earth. Sedimentary rocks (sandstone, limestone, shale, conglomerate, gypsum), the least common, are formed through a gradual accumulation of sediments (sand, soil, etc.). Metamorphic rock (marble, slate, schist and gneiss) forms when existing rocks are heated and put under pressure beneath the Earth’s surface.

Some rocks I’ve seen in my town this month:

Even though the Grand Canyon (Arizona) is young in geologic time, carved out just 6 million years ago, it’s got rocks that range from 1840 million years old (1.84 billion years old) to 270 million years old, as well as younger rocks, like Ice Age fossils and some debris flow deposits that form each year.

My own state is filled with granite, mica, quartz, schist, slate, among others. You can see the bedrock map here for “the Granite State.”

Next time you see a rock, think about all it’s been through, all that’s occurred in its mute presence, the places it’s been. And the place it’s come to rest for now, with you.

*

“I wonder if you, like me, feel, just now, like a ghost in the sunlight, awash in memories …” — Hilton Als

*

Thanks for checking in. Be sure to see what the other 31 Dayers are writing about.

*