Since childhood I have loved looking through a telescope at the faint wisps of light that reach us from distant galaxies. I've long known that the starlight from these faraway objects is old and that those galaxies appear not as they are now but as they were millions or even billions of years ago. When I look at galaxies of the spectacular Virgo Cluster, I am seeing them as they were some 50 million years ago (by comparison, dinosaurs became extinct 65 million years ago).
As a biology teacher, I am acutely aware of another universe, one that is within us, one of thought, feeling, and memory. This inner universe consists of as many interacting cells as there are stars in the Milky Way. Electrochemical impulses flick between the myriad brain cells in ways we are only beginning to understand. The power of the brain is immense, but can that brain fathom immense quantities of time? Can we compresend the length of the journey made by the ancient light that softly glows in the eyepiece of the telescope?
I have found a way to imagine the depths of time. It involves three seemingly unrelated phenomena: the dynamics of the Earth-Moon system, the skeletons of corals that lived 400 million years before the human species arose, and a wonderful animal called the nautilus.
In the 18th century, Edmond Halley noted discrepancies between predicted and observed positions of solar eclipses and showed that these deviations resulted from the gradual slowing of the Earth's rotation. Immanuel Kant, the philosopher, correctly suggested that tidal friction causes the slowing. The Moon's gravity causes ocean tides that, as they lap against shorelines, dissipate the energy of the Earth's rotations. The rate of slowing is about 0.00002 second [20 microseconds] per years; that is, every 50,000 years the day becomes one second longer.
Until the 1960s, the only evidence supporting the rotational slowing came from astronomical observations. Then paleontologist John Wells found that certain long-dead corals contain in the annual rings within their fossilized skeletons a record of the passage of days and years. Within the rings are fine laminations that record daily deposits of calcium carbonate by the coral polyp within the skeleton.
Careful examination of fossil corals from previous geological periods spanning millions of years reveals that the average number of laminations within each set of rings increases as one searches further and further back into time. For example, in the Devonian period, some 370 million years ago, fossil corals contain an average of 400 laminations per ring. This indicates that the corals lived through a year of approximately 400 days, with each day only about 22 hours long. Does 0.00002 second per year make a difference? It would seem so.
This story has an additional dimension because the slowing of Earth's rotation affects the Moon. Earth and the Moon revolve around a common center of gravity. This point lies deep inside Earth because of the far greater mass of Earth. The angular momentum of the two bodies (the product of their masses and velocities) remains constant, so as Earth loses momentum as its rotation slow, the orbital momentum of the Moon increases. This causes the Moon to accellerate in its orbit and slowly withdraw from the Earth.
Paleontological evidence shows the lunar recession. Consider the champered nautilus, a cephalopod related to octopuses and squids. Once nautiluses were a mighty group, 10,000 species strong. But like so many other tribes, most have disappeared. Today only a scant five species remain. The nautilus lives within a shell and, as it grows, it secretes a new chamber into which it moves. The animal then seals off the old chamber with a septum, or wall. Between the septa of present-day nautiluses is an average of 30 fine laminations, which suggest that each lamination represents one day and the secretion of the septa is tied to the 30-day lunar month.
Fossil nautiloids show an almost linear decrease in the number of laminations per chamber as one examines progressively older specimens. The youngest fossil nautiloids have about 25 lamina per chamber. In the Ordovician period some 420 million years ago, each chamber contains only nine or ten laminations. The lunar cycle in the Ordovician must have been only nine or ten days.
From Kepler's laws of planetary motion, astronomers can deduce the Moon's distance in the past from its present distance, present orbital period, and past orbital period. A 10-day month means that the Ordovician nautiloids saw a gigantic Moon at a distance of about 100,000 miles -- just over 40 percent of its present distance. Their day would have been about 21 hours long at a rotational slowing rate of 0.00002 second per year, and each year would have had 417 days, assuming no change in Earth's orbit around the Sun.
The Grand Canyon is one place in the United States where one can peer back into the Ordovician. Recently, I stood at its rim at sunset and could see the colorful layers of rock that show so much of Earth's long history. The great chasm yawned beneath me, full of light, darkness, and shadows. I imagined I was standing at the edge of the abyss of time. I thought back 420 million y4ears to those ancient Ordovician nautiloids, whose strange eyes had witnessed a gigantic Moon that raced through all of its phases in just ten days. Trying to comprehend the vast amount of time that had passed since those nautiloids swam in their ancient ocean made me giddy.
In the rocks of central and western Texas, I have found ancient corals and nautiloids. When I hold the fossils in my hands, they speak to me in haunting voices. For me, they carry messages from deep time: Astronomy is not only over our heads but under our feet as well. next time you look through your telescope across the light-years to a distant galaxy, remember that seemingly insignificant 0.00002 second per year. Ponder its dramatic effect upon the Moon and the amazing record in the crust of our beautiful planet, unknowingly preserved by those corals and nautiloids.
Edward Greding, Jr., is a professor of biology at Del Mar College in Corpus Christi, Texas. http://news.bbc.co.uk/hi/english/sci/tech/newsid_956000/956126.stm:
Bands indicate tidal movements billions of years ago By BBC News Online science editor Dr David Whitehouse
The Earth's oceans were being tugged by tides more than three billion years ago, according to an analysis of rocks in South Africa.
The sandstone and shale deposits, which were found in the Moodies group of hills, have markings that scientists say were made by the ebb and flow of waters moving along a continental shoreline.
The study proves that the Moon was orbiting the Earth in a roughly similar orbit to the one it occupies today.
The tidal research has been published in Geology, the journal of the Geological Society of America.
The scientists examined rocks exposed on the banks of the Sheba River in Mpumalanga province.
Dating showed the deposits were laid down 3,225 million years ago, in a shallow lagoon on the edge of a continental margin.
Strengths of the tides
Close inspection revealed markings indicating the various times during the tidal cycle when silts would have been deposited - such as in an ebb tide when the waters moved back from the shore.
Other patterns in the rocks revealed the neap-spring-neap tidal cycle, as well as variations in the strengths of the tides.
Dr Eriksson, of the Australia National University in Canberra, explains the evidence as due to variations in the pull of the Moon depending how far or how close the satellite was to Earth in its orbit.
He told BBC News Online: "In my mind this represents unambiguous evidence for tides on Earth some 3,200 million years ago, and implies the presence of the Moon in orbit around the Earth at that time."
The analysis of the tidal patterns also suggests that the duration of the lunation, the length of the lunar month, was 20 days as opposed to the 27.5 days today.
"The nature of the cyclicity indicates that the Moon was in a near-circular orbit similar in shape to the present orbit. This is consistent with the idea that the Moon formed after a giant impact and was not a separate body that was captured by the Earth.
The Geology paper was co-authored by Edward Simpson from Kutztown University, Pennsylvania, US.