Thursday, May 26, 2016

How Old Are We?


The cosmic age problem is a historical problem in astronomy concerning the age of the universe. The problem was that at various times in the 20th century, some objects in the universe were estimated to be older than the time elapsed since the Big Bang, as estimated from measurements of the expansion rate of the universe known as the Hubble constant, denoted H0.

Since around 1997–2003, the problem is believed to be solved by most cosmologists: modern measurements give an accurate age of the universe of 13.8 billion years, and recent age estimates for the oldest objects are either younger than this, or consistent allowing for measurement uncertainties.

Many of my Christian friends tell me the world is six thousand years old. Science says otherwise. I don't have a problem either way, but I've been told if I don't believe the world is six thousand years old, then I'm going to hell. I've also been told by atheists what an unaware idiot I am. I don't begrudge them their opinions because, yes, sometimes I am an idiot. However, sometimes so are they so it appears to balance out. My idiocy against yours. I will add that the current understanding of a quantum universe allows for the most dogmatic creationism so if you fancy yourself a scientist, don't forget there are a number of fascinating new theories on how reality maintains itself. It's not a clockwork universe, apparently.

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. The most famous came in 1654, when Archbishop James Ussher of Ireland offered the date of 4004 B.C.

Within decades observation began overtaking such thinking. In the 1660s 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. Robert Hooke, not long after, suggested that the fossil record would form the basis for a chronology that would “far antedate ... even the very pyramids.” The 18th century saw the spread of canal building, which led to the discovery of strata correlated over great distances, and James Hutton’s recognition that unconformities between successive layers implied that deposition had been interrupted by enormously long periods of tilt and erosion. By 1788 Hutton had formulated a theory of cyclic deposition and uplift, with the earth indefinitely old, showing “no vestige of a beginning—no prospect of an end.” Hutton considered the present to be the key to the past, with geologic processes driven by the same forces as those we can see at work today. 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.

The oldest dated rocks on Earth, as an aggregate of minerals that have not been subsequently broken down by erosion or melted, are more than 4 billion years old, formed during the Hadean Eon of Earth's geological history. Such rocks are exposed on the Earth's surface in very few places. (Some meteorites, such as the ALH84001 Mars meteorite found in the Allan Hills of Antarctica, are older but they were not formed on Earth).

Some of the oldest surface rock can be found in the Canadian Shield, Australia, Africa and in a few other old regions around the world. The ages of these felsic rocks are generally between 2.5 and 3.8 billion years. The approximate ages have a margin of error of millions of years. In 1999, the oldest known rock on Earth was dated to 4.031 ± 0.003 billion years, and is part of the Acasta Gneiss of the Slave craton in northwestern Canada. Researchers at McGill University found a rock with a very old model age for extraction from the mantle (3.8 to 4.28 billion years ago) in the Nuvvuagittuq greenstone belt on the coast of Hudson Bay, in northern Quebec; the true age of these samples is still under debate, and they may actually be closer to 3.8 billion years old. Older than these rocks are crystals of the mineral zircon, which can survive the disaggregation of their parent rock and be found and dated in younger rock formations.

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