On a Saturday morning, your restless kindergarten daughter asks you, “What’s time?” You reply “8:30.” Not what she wants. “What is time?” You give her, “It’s days and nights, minutes and hours, years and months.” “Yeah, but what is it? Can you see it? Can you hear it? Can you eat it?” Hmmm.
So, you get out the family’s musty dictionary and quote from it, time is “a nonspatial continuum in which events occur in apparently irreversible succession from the past through the present to the future.” Or you check Wikipedia and you get, “Time is the indefinite continued progress of existence and events that occur in an apparently irreversible succession from the past, through the present, into the future.” She rolls her eyes and says, “I’m going outdoors to see if the pussy willows are out yet.”
Time is one of the most abstract concepts that influence our lives: time, love, infinity, and many more. And yet, time has a vital place in nature, providing measures of time in our part of the Solar System for over 4 billion years. These natural measures of time come from just three pieces: 1) the Sun, with great mass, heat, light, and gravity; 2) the Earth, where life has existed for at least 2.5 billion years; and 3) the Moon, the result of a cataclysmic impact when the young earth was struck by a “proto-planet” named Theia and produced a molten mass that became our moon, affected the rate of the earth’s rotation, and perhaps shaped the earth’s orbit around the sun.
These three orbs give us years, months, and days, the only measures of time produced by nature. The other measures of time – centuries, weeks, hours, minutes, seconds - have been created for the convenience of our species. A Bristlecone Pine does not ponder the centuries it has lived; the days of a week are irrelevant to seaweed; a giraffe does not know the hours in each of its days; a daffodil doesn’t count the minutes until sunset; and a mayfly doesn’t spend its short life tallying seconds.
Seconds are intriguing because scientists have created an atomic and mathematical definition of seconds upon which other measures of time can be extremely precise in your digital watch, the launch moments of spacecraft, or the fastest ever 100-yard dash. The accepted, precise definition of a second in an atomic clock is: “The duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium 133 atom.” Try that one on your kindergartener.
Science has also found many answers to how plants and animals respond to the natural measures of time – years, months, and days. The evidence suggests that around 2.5 billion years ago, these rhythms of the earth, sun, and moon were in place, but life was just coming into the picture in the form of organic molecules and primitive cells forming in the chemical soup of ancient oceans. The cells that were successfully surviving and replicating were those that responded to these rhythms, depending upon timely light, heat, food. DNA and chemical activities within living cells were the tools for adapting to these external measures of time.
Ultimately the external cycles stimulated internal biological cycles in those cells. As life forms became more complex, the external stimulation of natural rhythms affected their vital activities such as stages of development and growth; reproductive success; and species-specific behaviors and adaptations such as diurnal or nocturnal activity; migration; hibernation; movement; cycles of enzyme and hormone activity; and many more. With that legacy, all existing life forms – every species - have evolved internal clocks and calendars that align with external rhythms. Biologists have studied these innate cycles, some are year-long calendars, some track monthly tides, and the most abundant are the daily (circadian) rhythms of life, with their evolved instructions from DNA, hormones, and enzymes.
The year calendar is determined by the axis-tilted Earth’s revolving around the sun, reliably creating seasonal conditions, such as climate, day length, and the location of sunrise and sunset, as well as the apparent revolving of the night sky’s star patterns. This calendar sets the internal annual calendars of living plants and animals. Once set, these innate calendars remain active and guide behavior until they get out of rhythm with the external calendar that will reset the innate clocks and calendars. How do long-distance migratory birds, sea turtles, or Arctic herds of caribous, know when they must leave and remain on track? The innate calendar.
The moon’s monthly (“moonthly”) journey around the earth reveals a sequence of phases and shapes the schedule of the tides. “Edge habitats” are the richest in biomass production and species diversity. The edges of Earth’s oceans are the most productive in these ways. Species of plants, vertebrates, and an extraordinary diversity of invertebrates – mollusks, arthropods, sponges, worms, and jellyfish are all tuned to the tides. The gravity of the moon and sun create tide cycles both monthly and daily because of the Earth’s rotation. Spend a month on the edge of the Bay of Fundy in Downeast Maine, and you’ll see the dramatic tides that raise the water level 8 to 20 feet. The highest monthly tides are known as Spring Tides, the result of the moon and sun are both in line with the Earth.
Two of my favorite critters live in the tidal zone. Grunions are small fish that ride the Spring Tides in southern California and wash up on the beach by the millions, where they lay their eggs. The males wrap around the females and deposit their sperm. Within 10 days the fertilized eggs hatch, and five days later the tiny fish wash away in the second Spring Tide of the month. On the east coast, Horseshoe Crabs have been using the Spring Tides to deposit their eggs in the damp upper beach sand where males do their part. Like Grunions, then the tiny larvae from the recent eggs wash into the ocean. Their monthly cycle has been absorbed as an innate cycle for over 400 million years. Their eggs serve another annual cycle, nourishing migrating shorebirds.
Circadian (daily) cycles have been studied for years. While they generate innate daily cycles, plants have a host of cyclic activities – leaves tracking the sun; opening and closing flowers; releasing pollen, and distributing their fruits and seeds. Humans, too, have a complex set of bodily functions driven by innate 24-hour cycles in our brains and affect our sleep, temperature, mental acuity, blood pressure, and comfort. Even if not exposed to the environmental cycles of the day and night, your innate cycles remain. Search “circadian cycle” to find charts of how we respond to these cycles. Better yet, have your kindergartener search it and then find her pussy willows. It’s their time.