The Shape and Future of the Earth

                                                              

“It’s tough to make predictions, especially about the future.”

–Yogi Berra

 

By Edwin D. Reilly, Jr.

For The Sunday Gazette

 

 It is with great sadness that I note that the University at Albany is phasing out its geology department, and this comes at the very time when more, not less, study of our fragile Earth is so much needed. Climate scientists agree that the Earth is warming, but have a hard time projecting exactly what will happen over the short term—the next hundred years, say. But, ironically, they are more certain about what, if not quite when, certain things will happen over the next few billion years.

 

The shape of the Earth

 

Spaceship Earth is remarkably stable, but not unchanging. Since its formation about 4.5 billion years ago, most of its rough edges have smoothed out, although mountains continue to rise and fall and the continents move about on their tectonic plates. Currently, the highest point above sea level is Everest at 29,028 feet, and the Marianus Trench under the Pacific is 35,798 feet deep. But these deviations from the surface of the Earth are insignificant compared to its almost 4,000 mile radius. Viewed and measured from afar, the shape of the Earth is much closer to a perfect ellipsoid than a billiard ball is to a perfect sphere, the deviations therefrom being 0.17% and 0.22% respectively.

 

Land features affect climate

 

Mountains obviously affect weather patterns that endure long enough to be called climates, as do the positions of the continents. A mere 250 million years ago, 1/18 the age of Earth, but long before there were humans, Earth had only one megacontinent, one now called Pangaea. It looked like a capital C, or to me, like the side view of a Roman soldier’s helmet (see illustration at top). Clearly, the climate in the middle of Pangaea must have been vastly different than anything we find on Earth today, and will be the next time the current continents meet again, especially if internal seas such as the Mediterranean are squeezed dry. The continents as we know them are still separating, Africa and South at the rate our fingernails grow, but eventually they will again coalesce.  Will Neo-Pangaea again be shaped like a helmet? Probably not. But the intelligent creatures that get to find out, in perhaps another 250 million years, are unlikely to look like humans and, if any exist to walk or crawl or fly over it, they may be of a species that evolves from some critter other than us.

 

The life of the Earth

 

How much longer might the Earth endure? No longer than our sun, of course, which has a probable additional lifetime of at least another five billion years before it explodes. But the Earth’s remaining life, or our own upon it, could be cut short through collision with a sufficiently large asteroid. On March 23, 1989, an asteroid with a diameter as big as a football field missed the Earth by a mere 400,000 miles. If that does not seem close to you by distance, consider the minor difference in time: the asteroid passed through the exact point that Earth had occupied just six hours earlier. The impact, had it occurred, would have created the largest explosion in recorded history. It is widely believed that a much larger asteroid that fell on the Yucatán Peninsula sixty-five million years ago caused the mass extinction of the dinosaurs and many other living things.      

 

Why are there seasons?

 

 We learned in grammar school that we on Earth experience seasonal changes because, relative to the plane of the Earth’s orbit around the sun, our planet happens to be inclined—“tilted” if you wish— by about 22.5 degrees. Clearly, if that were to change significantly, climate would change with it. More tilt, and we’d have hotter summers and colder winters; less tilt, the reverse. And the tilt does vary, ranging from 22.1 degrees to 24.5 degrees and back again in a 41,000-year cycle. This cycle is one of several different cycles discovered by one Milutin Milanković (1879-1958), a Serbian geophysicist best known for his theory that ice ages are caused by a combination of changes in the sun and variations of the Earth’s orbit.


Milanković is also the scientist who, in 1923,  formulated a leap-year rule for the Revised Julian calendar that differs from the one of the Gregorian calendar used by most of the world, in contrast to the Revised Julian in use by only a few countries. In the Gregorian, century years, those divisible by 100, are not leap years unless they are also divisible by 400 (which is why 2000 was a leap year). The
Milanković rule is that century years are not leap years unless, when divided by 900, the remainder is either 200 or 600, so that 2000 was a leap year by his standards too. The variant rules will not produce a different result until the year 2800, a leap year for those living in that centennial year who still observe the Gregorian calendar but not one in the Revised Julian. (I am indebted to Dr. Jack Underwood of Schenectady who, in a letter to the Gazette of 6/17/2007, pointed out in a very gentle way that I had botched the leap-year discussion of my original article.)

 

Short term changes

     

A mere change in the weather can seem like climate change if a pattern endures long enough. In North America and comparable latitudes in Europe and Asia in 1816, “The year without a summer,” lakes and rivers were still partially frozen in late June, due to the explosion of Mount Tambura in the Dutch East Indies in August of the year before. Then on August 26, 1883, the volcano on the island of Krakatoa erupted, ejected about ten cubic miles of rock, ash, and pumice high into the atmosphere, and, directly or indirectly through tidal waves, killed 36,417 people. Scattering of the suns rays from the added atmospheric dust caused spectacular sunsets all over the world for many months. A blood-red sky supposedly inspired Edvard Munch to paint his famous series of Scream paintings (though not until a decade later). By 1884, the Earth’s average temperature fell by a bit over 2 degrees Fahrenheit and did not return to normal for another year.

 

How long is a day?

 

Climate certainly depends on the length of a day, and that length has changed drastically over 4.5 billion years because the Earth’s rotation is slowing down by 1.7 milliseconds per century due to the friction of sea and atmospheric tidal forces. When the Earth was very young, its days were but six hours long. After 1.3 billion years, the length of a day reached 15 hours. And if the nuclear fuel of “That Lucky Old Sun” (my tribute to Frankie Laine, who died four months ago) can hold out for another 20 billion years so it can “Roll Around Heaven All Day,” a day that will be as long as two are now and I’ll finally be able to get enough done in one of them.  

 

Edwin D. Reilly, Jr. lives in Niskayuna and is a regular contributor to the Sunday Gazette opinion page.