Hundreds of millions of years ago, single-celled organisms recorded in rock the interactions of the Sun, Earth, and the Moon. Ancestors of blue-green algae built concentrically layered mounds resembling cabbage heads called stromatolite structures by cementing sediment grains together with glue like substance secreted from their bodies. As with modern stromatolites, the ancient stromatolite colonies grew in the intertidal zone, and their height was indicative of the height of the tides during their lifetime. This is because stromatolites grow between the low-tide mark and the high-tide mark.rnThe stromatolite structures also tilted toward the Sun as they grew. This phenomenon is known as heliotropism (helio meaning “sun”), which is the inclination of a structure toward the average direction of sunlight. Stromatolites found in the Bitter Springs Formation in central Australia provided an 850-million-year-old fossil record of the Sun’s movement across the sky. A stromatolite situated near the equator pointed south in the winter and north in the summer and developed a growth pattern in the shape of a sine wave.rnIf new sediment layers were constructed each day, then the number of layers appearing in one wavelength represented the number of days in a year during the time of the stromatolites growth. By counting the layers in stromatolite fossils, researchers have estimated that approximately 435 days constituted a year (the time required for the Earth to complete one revolution around the Sun) during the late Proterozoic. The results agreed well with those of counting the growth rings of ancient coral fossils to estimate the number of days in a year going as far back as the beginning of the Cambrian period, 570 million years ago. The studies indicated that the Earth was spinning faster on its axis and that the days were only 20 hours long.rnIn addition, the sine wave patterns of ancient stromatolites contained information about the maximum travel of the Sun across the equator. The equator forms an oblique angle to the plane of Earth’s orbit around the Sun, called the ecliptic. This angle is controlled by the tilt of the Earth’s rotational axis. The maximum latitude of the Sun during the peak of each season is obtained by measuring the maximum angle at which the sine wave deviates from the average direction of stromatolite growth. Today, the Sun travels 23.5 degrees north of the equator during the summer and 23.5 degrees south of the equator during the winter. However, about 850 million years ago, this value was about 26.5 degrees, an indication that the climate at that time would have been much more seasonal than it is today. This observation supports the idea that the axial tilt angle has been decreasing with time.rnPresent-day stromatolites live in the intertidal zones, above the low-tide mark, and their height is indicative of the height of the tides, which is mostly controlled by the gravitational pull of the Moon. The stromatolite colonies of the Warrawoona group in North Pole, Western Australia, at 3.5 billion years, the oldest on Earth, grew to tremendous heights with some over 30 feet tall.rnThis suggests that an early age the Moon was much closer to the Earth, and because of its stronger gravitational attraction at this range, it raised tremendous tides that must have flooded coastal areas several miles inland.rnThe data also explain why the length of day was much shorter. The early Earth rotated much faster than it does today, and as its rotational rate gradually slowed as a result of drag forces produced by the tides, some of its angular momentum (rotational energy) was transferred to the Moon, flinging it out into a wider orbit. Even today, the Moon is receding from the Earth at a rate of about two inches per year.rnThe solar cycle is a periodic fluctuation of solar output, occurring today about every 22 years, double the 11-year sunspot cycle. Evidence for a solar cycle operating as far back as the Precambrian is thought to exist in 680-million-year old glacial varves, or banded deposits, found in lake bed sediments north of Adelaide in South Australia. The varves consist of alternating layers of silt deposited annually during the late Precambrian ice age. Each summer when the glacial ice melted, sediment-laden melt water discharged into a lake below the glacier, and the sediments settled out to form a stratified deposit. During times of intense solar activity, the Earth’s climatic temperature increased slightly, causing more glacial melting and the deposition of thicker varves. By counting the layers of thick and thin varves, scientists can establish a stratigraphic sequence that mimics the 11-year sunspot cycle, the occurrence of large numbers of sunspots on the Sun’s surface, and the 22-year solar cycle or possibly even the early lunar cycle, covering the full range of lunar orbital variations, which today is about 19 years. Another type of stratified deposit, which might well be the most beautiful, valuable, and enigmatic rock ever created on the planet, occurs in banded iron formations. Composed of alternating layers of iron and silica, they were formed about 2 billion years ago at the height of the earliest ice age. For unknown reasons, major episodes of iron deposition coincided with periods of glaciation. Evidently, on average the oceans were much warmer at that time than they are at present. When iron- and silicate-rich warm currents flowed toward the glaciated polar regions, the suddenly cooled waters could no longer hold the minerals in solution. They thus precipitated out, forming alternating layers due to difference in settling rates between silica and iron, the heavier of the two minerals. Volcanic eruptions are also known to follow the 11-year solar cycle, which is a slight waxing and waning in the sun’s energy output. The study of hundreds of eruptions over the past four centuries implies that the solar cycle might have had an influence on the time when volcanoes came to life. The eruptions appeared most numerous during the weakest portion of the solar cycle, when the numbers of sunspots are low. During the peak of the solar cycle, emissions from the Sun cause small but abrupt changes in the Earth’s atmosphere, jarring the planet slightly. This motion might trigger tiny earthquakes that relieve stress under volcanoes, thereby preventing a large eruption until the solar cycle is again at a minimum, when the pent-up volcanoes blow their tops.
Joseph Kiefferrnhttp://jewelryuk.orgrnfrom:
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