"The Earth from here [the Moon] is a grand oasis in the big vastness of space." – Jim Lovell, Apollo 8 Astronaut
Following months of flooding, the Illinois River was finally approaching what might be termed its normal, low-water level for the summer. The sandy beach and seeps at Quiver Lake were once again exposed. Great egrets, great blue herons, and killdeer could now find appropriate foraging areas in the shallows. And Caspian terns and ring-billed gulls gathered on exposed mud flats further from shore. I sat on the bluff side just above the beach and tried to avoid thinking about the daunting task before me: clearing the beach of the massive tangles of twigs, branches, and large logs left behind from the floodwaters.
Then a slight movement at the water’s edge caught my attention: a lone shorebird called a pectoral sandpiper, walking along in the wet sand and occasionally grabbing minute food items from the ground. It was early August, and the fall shorebird migration had begun; many other species would follow and perhaps thousands of individuals. I stood still and thought about this small bird, traveling from its high Arctic nesting area to South American overwintering habitats, stopping briefly at this particular location in Illinois to gather enough food energy to continue its journey. It’s easy to feel insignificant when faced with a small bird capable of such a great feat, recognizing no international boundaries, local authorities, or governments. An authentic being of the world that illustrates how truly connected and one this world really is.
And yet my thoughts immediately veered in the opposite direction. And I was struck by the fact that although the earth may be an interconnected whole from a sandpiper’s perspective, from the standpoint of geopolitics, it may never have been more fragmented…and, of course, dangerous. I feel safe at my home and lakeside cabin in a quiet rural atmosphere far from any major city, and most of the time, life is relatively carefree. But it is really the privilege of living in the United States that allows this life, just one result of all who have sacrificed and fought for such a country to exist. The daily news helps keep me in touch with the rest of the world, but most of it is not good, reminding me of murderous ideologies, corruption, oppression, and, what seem to be, insurmountable obstacles to progress. I want to know what is happening; but the newspaper is not an inducement for international travel.
Unlike me, though, the sandpipers that I watch along the beach have no choice. They must make the yearly journeys across the globe to complete breeding cycles and survive to the next season, immersed in their own world of continual danger; high alertness and wariness are quite obvious as the sandpipers frequently check surroundings for predators, who are themselves highly attuned to any gap in the sandpipers’ defense strategies. To these creatures, danger is ever present as an accepted fact of life.
In any case, it is the long summer days on the northern tundra combined with a superabundance of insect life make the migration worth the risk and effort. At the other extreme of each year are nights equally as long as the summer daylight hours but with brutal, freezing weather. And, of course, it is these extreme seasonal changes that shaped bird migration in the beginning, a direct result of the Earth’s axial tilt of 23.5 degrees relative to the ecliptic plane, defined as a baseline by the Earth’s elliptical orbit around the Sun. What if the tilt angle were zero? Then equal hours of daylight and night time would occur on each day at all latitudes, not just on the vernal and autumnal equinoxes, which would no longer exist. It’s the tilt, in fact, that causes the seasons—during summer, the Earth’s axis is tilted toward the Sun; and during winter, the tilt is away from the Sun—so with zero tilt, there would be no seasons. In that situation, for example, what is now Arctic tundra in northern Canada would probably be a perpetual winter. Without pronounced seasonal cycles, how differently evolved would be the planet’s biological communities (tundra, boreal forest, tropical rain forest, desert, grassland, etc.) and how would they be distributed across the globe? What would bird migration patterns be like?
An interesting aspect of this thought experiment is that there is nothing special about 23.5 degrees. Billions of years ago, a chance collision of the Earth with a planet-sized object is thought to have caused the tilt (i.e., pushed the Earth over), which happened to settle out at 23.5 degrees, plus or minus a certain amount of variation on a 40,000-year cycle. (Although I write this in a rather matter-of-fact manner, the unimaginable violence of such an event has not escaped me.) Other planets in the Solar System have different axial tilts; for example, Jupiter is only 3 degrees, while Uranus is at 98 degrees (so Uranus, in effect, rolls around the Sun on its side).
Photo from Apollo 8, downloaded from NASA.
Following such thoughts, the images meandering through my mind are far removed from the Illinois River backwaters and pectoral sandpipers. Then as my consciousness returns closer to home, I recall the iconic image of Earth from 1968, captured by the crew of Apollo 8, the first manned spacecraft to orbit the Moon. In that photograph, the Earth appears as an interconnected whole. The sandpiper’s perspective! But, with its thin wisp of an atmosphere, our one and only home planet, shining against the dead blackness of space, also seems fragile, vulnerable, and…quite improbable.
References
Kutter, G.S. 1987. The universe and life. Jones and Bartlett Publishers, Inc. Boston/Portola Valley.
All About Birds. www.allaboutbirds.org referenced 14 August 2019.
National Aeronautics and Space Administration. www.nasa.gov referenced 14 August 2019.
Universe Today. www.universetoday.com referenced 14 August 2019.