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Uncovering Earth's Age: A Deep Time Mystery
Genesis 1:1, 1:9, 1:10
In the Beginning, God created the heaven and the Earth. Then God commanded, “Let the water below the sky come together in one place, so that the land will appear”—and it was done. He named the land “Earth,” and the water which had come together he named “Sea.”
Early Theological Attempts
Since recorded time, man has contemplated enduring mysteries that persist today. Theories for the formation and age of our solar system and the earth we live on have been attempted time and again. Prior to the Age of Enlightenment, the Church was the authority on any such questions of origins. And when people began to ask serious questions about the exact age of the earth, the church was more than happy to accommodate. In one famous account, In 1654, Archbishop Usher (Ireland), based on genealogy in the Bible, determined that earth was created October 26, 4004 BC, 9:00am (PST). Therefore, the Earth was 6000 years old. Other Bible sourced calculations all arrived at similar estimates of 6,000 years old that - amazingly - is still believed by fundamentalists today. Serious scientific study and discovery wasn't available at that time and it would of course be impossible for authors of the bible to provide any serious data that we use today.
Chronology of Modern Dating Techniques
By the 17th Century, geological observation began to overtake such thinking. But the Earth is very good at covering its tracks and would not reveal its secrets easily. Erosion, volcanic eruptions, plate tectonics and continental drift would confound and confuse investigators for centuries. The rock cycle, as we now know, is driven by plate tectonics, with sedimentary material vanishing into subduction zones such as the one found in the marinas trench. In his book, The origin of Continents and Oceans, the meteorologist Alfred Wegener described in 1915 what he called continental drift - a theory that would develop into plate tectonics some fifty years later. And the oceans have long since approached something close to a steady state, with chemical sediments removing dissolved minerals as fast as they arrive.
- In the 1660’s, Nicolas Steno formulated concepts of deposits of horizontal strata and noted different strata contained different types of fossils.
- In 1778, Belsazar Hacquet was the first geologist to distinguish limestone from dolomite and that sedimentary limestone and chalk was made mostly from the skeletons of marine life which accumulated at the bottom of shallow seas.
- By 1788 James Hutton had formulated a theory of cyclic deposition and uplift, with the earth indefinitely old. Hutton recognized that unconformities between successive layers implied that deposition had been interrupted by enormously long periods of tilt and erosion and realized this would take millions of years. His theory became to be known as uniformitarianism.
Further investigation would come from not only geologists, but from other investigative scientists as well and would eventually arrive at a solution.
- In 1862, the physicist William Thomson (Lord Kelvin) published calculations that fixed the age of Earth at between 20 million and 400 million years. He assumed that Earth had formed as a completely molten object, and determined the amount of time it would take for the near-surface to cool to its present temperature. His calculations did not account for heat produced via radioactive decay (a process then unknown to science) or convection inside the Earth, which allows more heat to escape from the interior to warm rocks near the surface.
- In 1897, Physicist Ernest Ruthaford figured out that measuring radioactive decay could accurately date the age of rocks. Rock samples from around the globe were found to be not just millions but billions of years old. A timescale referred to now as “deep time.” However, rocks from the earliest stages of earth history are very hard to find and in fact may no longer even exist. The oldest known rock on earth dating to 3.8 billion years ago.
- In the 1950s Clare C. Patterson, a geologist, tried a new approach using meteorites. He knew that meteorites must have clumped together from the same minerals in space that formed the earth but were not subject to the erosive nature of rocks on earth. Aging these meteorites once again provided an answer of billions of years old.
Radiometric aging of the earth works like this: Particular isotopes of a radioactive element decays spontaneously into another element at a distinctive rate such as uranium into lead. This rate is given in terms of a "half-life", or the amount of time it takes half of a mass of that radioactive material to break down into its "decay product". Some radioactive materials have short half-lives; some have long half-lives. Uranium and thorium have long half-lives, and so persist in earth's crust. Since this is the measurement of decay on an atomic level, it is highly accurate. and suggested to scientists that it might be possible to measure the age of earth by determining the relative proportions of radioactive materials in geological samples. When scientists apply radiometric dating to a wide range of material samples from earth’s mantle, our moon and also meteorites (present during the formation of the solar system) the answer that comes back is approximately 4.567 billion years for meteorites old with a range of dates for other material as follows:.
- The oldest rocks on Earth, found in western Greenland, have been dated by four independent radiometric dating methods at 3.7-3.8 billion years. Rocks 3.4-3.6 billion years in age have been found in southern Africa, western Australia, and the Great Lakes region of North America. These oldest rocks are metamorphic rocks but they originated as lava flows and sedimentary rocks. The debris from which the sedimentary rocks formed must have come from even older crustal rocks. The oldest dated minerals (4.0-4.2 billion years) are tiny zircon crystals found in sedimentary rocks in western Australia.
- The oldest Moon rocks are from the lunar highlands and were formed when the early lunar crust was partially or entirely molten. These rocks, of which only a few were returned by the Apollo missions, have been dated by two methods at between 4.4-4.5 billion years in age.
- The majority of the 70 well-dated meteorites have ages of 4.4-4.6 billion years. These meteorites, which are fragments of asteroids and represent some of the most primitive material in the solar system, have been dated by 5 independent radiometric dating methods.
- The "best" age for the Earth is based on the time required for the lead isotopes in four very old lead ores (galena) to have evolved from the composition of lead at the time the Solar System formed, as recorded in the Canyon Diablo iron meteorite. This "model lead age" is 4.54 billion years.
Other Dating Methods
Of course, there are other dating methods in use today:
Carbon 14 Dating – accurate for material no more than 50,000 years old. While sometimes subject to error, carbon dating is reliable and dating of organic material and fossil remains show a consistent pattern of age in conjunction with surrounding sedimentary column strata.
DNA Mutation Dating – upper limit accuracy of 150,000 years. Helpful for determining the migration of early hominids out of Africa.
Paleomagnetic Dating – accurate up to 1 billion years ago - The study of the record of the Earth's magnetic field in rocks, sediment, or archeological materials. About every 250,000 years, the earth changes its magnetic polarity direction from North to South and back again. Certain minerals in rocks lock-in a record of the direction and intensity of the magnetic field when they form. This record provides information on the past behavior of Earth's magnetic field and the past location of tectonic plates
Radiometric Dating of other matierals (potassium-argon; argon-argon)– accurate to 3.8 billion years
Spectral and luminosity classification system, –The evidence for the antiquity of the Earth and Solar System is consistent with evidence for an even greater age for the Universe and Milky Way Galaxy. a) The age of the Universe can be estimated from the velocity and distance of galaxies as the universe expands. The estimates range from 7 to 20 billion years, depending on whether the expansion is constant or is slowing due to gravitational attraction. b) The age of the Galaxy is estimated to be 14-18 billion years from the rate of evolution of stars in globular clusters, which are thought to be the oldest stars in the Galaxy.
The Big Picture
With many of the longstanding questions answered, geology and astronomy combined to form a modern day picture of how the earth was created and developed 4.567 billion years ago:
The sun in our newly developed solar system was surrounded by a cloud of dust and gas. As the gases cooled, little grains of minerals formed that eventually began to coalesce into larger and larger objects. As these objects grew, their own gravity attracted more and more material until several planet sized formations where created. It is believed that the early earth was molten from the heat generated from the constant bombardment of meteorites and internal convection as well as heat generated from radioactive material. Heaver material, such as iron and nickel, was drawn deep into the earth’s core and the lighter material formed the outer thin crust with a super compact dense mantel in between. In fact, remnants of the material that created Earth are still drifting in space today in what’s known as the Kuiper belt, a belt surrounding the solar system which also contains Pluto with millions of objects.
It is theorized that liquid water arrived on earth from meteorites. Some of the oldest rocks found on earth prove oceans were forming as early as 4.28 billion years ago. Banded iron formations, in magnetite from these very old rocks could only have developed in the presence of water. Evidence contained within meteorites that we can find even today appear to also to have contained amino acids, the building blocks of life on earth. Finally, Cyanobacteria, or blue-green algae, produced the oxygen in our atmosphere leaving the remants of stromatilites (layered bio-chemical accretionary structures formed in shallow water), a major constituent of the fossil record as to first forms of life on earth and date to 3.5 billion years ago.