Geology how old is the earth

Published earlier this year, the collection draws articles from the archives of Scientific American. Aristotle thought the earth had existed eternally. Roman poet Lucretius, intellectual heir to the Greek atomists, believed its formation must have been relatively recent, given that there were no records going back beyond the Trojan War. The Talmudic rabbis, Martin Luther and others used the biblical account to extrapolate back from known history and came up with rather similar estimates for when the earth came into being.

Within decades observation began overtaking such thinking. In the s Nicolas Steno formulated our modern concepts of deposition of horizontal strata. He inferred that where the layers are not horizontal, they must have been tilted since their deposition and noted that different strata contain different kinds of fossil.

This position came to be known as uniformitarianism, but within it we must distinguish between uniformity of natural law which nearly all of us would accept and the increasingly questionable assumptions of uniformity of process, uniformity of rate and uniformity of outcome.

That is the background to the intellectual drama being played out in this series of papers. It is a drama consisting of a prologue and three acts, complex characters, and no clear heroes or villains. We, of course, know the final outcome, but we should not let that influence our appreciation of the story as it unfolds. Even less should we let that knowledge influence our judgment of the players, acting as they did in their own time, constrained by the concepts and data then available.

One outstanding feature of this drama is the role played by those who themselves were not, or not exclusively, geologists. Most notable is William Thomson, ennobled to become Lord Kelvin in , whose theories make up an entire section of this collection. He was one of the dominant physicists of his time, the Age of Steam.

His achievements ran from helping formulate the laws of thermodynamics to advising on the first transatlantic telegraph cable. Scientists have dated these rocks using uranium-lead isotopes at 4. Also, scientists recently reported 4. Narryer and the Jack Hills in Western Australia Nutman , which suggests the erosion of granite-like crust older than the oldest known preserved crust Cooper Thus, we can be confident that the minimum age for the Earth exceeds 4 billion years by examining Earth materials.

But old rocks do exist, says Reich, and the oldest rock we know is a tiny piece of zircon found in western Australia. The process of figuring out a rock's age often falls to the scientific techniques of radiometric dating , the most famous of which is radiocarbon dating. This process focuses on the ratio between the number of carbon and carbon isotopes in any once-living being: that ratio indicates how long it's been since that being was alive.

But carbon is not the only element that can be dated— a whole host of others exist. As the dating technology progressed, these methods proved unreliable; for instance, the rise and fall of the ocean was shown to be an ever-changing process rather than a gradually declining one.

And in another effort to calculate the age of the planet, scientists turned to the rocks that cover its surface. However, because plate tectonics constantly changes and revamps the crust, the first rocks have long since been recycled, melted down and reformed into new outcrops.

Scientists also must battle an issue called the Great Unconformity, which is where sedimentary layers of rock appear to be missing at the Grand Canyon, for example, there's 1. There are multiple explanations for this uncomformity; in early , one study suggested that a global ice age caused glaciers to grind into the rock , causing it to disintegrate. Plate tectonics then threw the crushed rock back into the interior of the Earth, removing the old evidence and turning it into new rock.

In the early 20th century, scientists refined the process of radiometric dating. Earlier research had shown that isotopes of some radioactive elements decay into other elements at a predictable rate.

By examining the existing elements, scientists can calculate the initial quantity of a radioactive element, and thus how long it took for the elements to decay, allowing them to determine the age of the rock. But rocks older than 3. Greenland boasts the Isua supracrustal rocks 3.

Samples in Western Australia run 3. Research groups in Australia found the oldest mineral grains on Earth. These tiny zirconium silicate crystals have ages that reach 4.