Al Stahler: Changing planet
Sometime in grade school, we’re given a map of the world, then tasked with coloring-in the land and seas. As fingers and crayons do their work, something becomes obvious: The beautiful fit between South America and Africa. Young brains call out, “What’s going on?”
Can you say “jig-saw puzzle”?
Something over two hundred million years ago, a dinosaur gazed up at the full moon, and saw the same pattern of dark and light we see on the moon today: The “man-in-the-moon”, painted across the moon by bright, rocky mountains, and dark, lava-filled basins. In two hundred million years, the moon’s dark-and-light pattern of mountains and basins has not changed.
Truth be told, the bright-and-dark moonscape has not changed in billions of years. The moon is a dead world. Deep down in its core – down in its belly – the moon is cold.
Suppose the early dinosaurs had invented space rockets, and had launched themselves to the moon.
Standing on the moon, dinosaurian astronauts looking toward Earth would have seen Earth’s surface, also painted in patterns of mountains and basins. But Earth’s pattern of mountains and basins, two hundred-plus million years ago, would have been very different from the pattern we see when we look at Earth from space today.
Earth’s core – Earth’s belly – is hot. Heat energy, rising up from our core, pushes things around on the surface of our planet, and the pattern of mountains and basins changes … big-time.
Powered by heat rising up from the belly of the Earth, North America and the Pacific Ocean basin both move across the face of our planet … in different directions, causing continent and ocean basin to grind against each other. They don’t grind smoothly; rock on both sides bends and stretches, building up stress. Several weeks ago, rocks east of the Sierra reduced some of that stress, breaking, slipping, twanging back. The sudden jerk was felt across the Sierra as a small earthquake [Soundings, The Union, 13 May].
Two hundred-plus million years ago, there was no North America … no South America … no Africa, Asia, Europe … no Pacific … no Atlantic. When the dinosaurs evolved, maybe two hundred-thirty million years ago, Earth boasted just one huge continent: The super-continent of Pangaea [pan-JEE-uh]. Pangaea was surrounded, in turn, by one humongous ocean.
Pangaea did not last long. Heat rising up from Earth’s belly pushed on it here, pulled on it there. The super-continent broke apart. Rifts developed between new continents; the rifts grew to become the basins of oceans.
North America pulled away from Eurasia; South America pulled away from Africa. Stretched thin, the floor of the rift between the western hemisphere (the Americas) and the eastern hemisphere, provided an easy route for heat to rise. Rift rock melted, feeding young volcanoes.
The rift widened … filled with seawater … and became the Atlantic. But even under water, the volcanoes continued to erupt … they erupt still, today. And the Atlantic continues to widen: The flight between New York and Paris grows longer by an inch-or-two, each year.
With copious heat in Earth’s belly – it’s hotter than the surface of the sun down there – the rifting of continents and creation of new ocean basins never ends. Here-and-there across the planet’s surface, rifts open up. Some evolve into new ocean basins; others simply cool down.
Eastern Africa’s Great Rift Valley – where humans first evolved – is one such rift, where the planet is attempting to create a new ocean. Volcanoes erupt on what is still dry land … as happened, late last month, in the Democratic Republic of Congo.
Sadly, the eruption of Mount Nyiragongo [neer-uh-GAHN-go] claimed lives. People lived on the sides that volcano … people live still on its slopes.
Why would people choose to live – to build their homes – on the sides of an active volcano? And to move back, after an eruption?
The politics and economics involved in such a decision are beyond the scope of this column. But there’s also biochemistry – the chemical reactions you and I perform in our bodies, the chemistry plants perform in theirs. We glue atoms together, to make the molecules (clusters of atoms) we need to survive. We un-glue atoms, take molecules apart, then re-glue those atoms back together, in new ways, to make new molecules.
To build the molecules we need, the right atoms must be available. We get some of those atoms from air and water, but we get most of them – especially the rare ones – from our food.
Plants pull these essential atoms from the soil. But the soil holds only so many of these atoms. When we harvest plants, these atoms do not return to the soil. And rain washes many atoms out of the soil. The soil becomes depleted.
Volcanoes bring fresh rock – full of fresh atoms – up from below. The soil around a volcano is rich in essential atoms. Aware of the risks, farmers from time immemorial have put down roots … built their homes … on the sides of volcanoes.
Nyiragongo is not erupting … this week. But it will erupt again … people will flee … and then will re-build … unless and until this piece of land … millions of years from now … becomes a new ocean basin.
IN THE SKY
Sunday, after sunset, red planet Mars will be right below the crescent moon.
Al Stahler enjoys sharing science and nature with friends and neighbors in The Union and on KVMR-FM. He teaches classes for both kids and grown-ups, and can be reached at email@example.com
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