Bad Science Is a Poor Response to Science Denial: The Age of the Earth and Lead's Role in Determining It
A cute meme circulating has a "Christian Against Science" declaring
The Earth is 4,000 years old. Change my mind.
A presumably more scientifically-inclined reply reads:
The half-life of uranium-238 is 4.5 billion years. It decays into radium-226 which in turn decays into radon-222. Radon-222 becomes polonium-210, which finally decays into a stable nuclide [sic], lead.
The existence of lead as an element disproves the 4000 year old myth.
Unfortunately that second sentence is incorrect, though the first may be accurate (I've not looked into it).
The issues.
- Yes, the Earth is more than 4,000 years old, and is in fact about 4.54 billion years +/- 1% in age. That's not the beef.
- Yes, radiometric dating using radioactive decay and ratios of lead isotopes and lead vs. other post-transition elements (notably Uranium and Plutonium) are in fact how the age of the Earth was first determined to any level of accuracy, in the early 20th century, and finally with about the present level of accuracy, to within about 50 million years, in the 1950s. (That research also uncovered some other interesting facts.)
- But NO, not all lead that exists is the result of the decay of heavier elements. In fact "The abundance of lead in the Solar System since its formation 4.5 billion years ago has increased by about 0.75%", from Wikipedia. So the mere existence of elemental lead is NOT in fact proof of the age of the Earth. The existence of some lead does however strongly support modern estimates. Whether or not the existence of lead at all is sufficient disproof of the 4,000 year age-of-the-Earth belief might depend on other factors and explanations. But it isn't due to the mechanism presented in this meme.
Scientific knowledge is based on accurate statements supported by evidence and/or experiment (though not necessarily the latter), as well as known mechanisms. The response in this meme actually fails this test. Its conclusion is correct (the Earth is more than 4,000 years old), its reasoning is false.
I'd also add that the usual fundamentalist Christian / Biblical age of the Earth is based on the Ussher Chronology, by 17th century Archbishop of Armagh and Primate of All Ireland James Ussher, who reckoned by Biblical evidence the date of Earth's creation to be October 23, 4004 BC, or 6,023 years and a few months old. In an extraordinarily rare instance of my citing the Institute for Creation Research as an authority on anything --- though as an authority on wrong answers, this seems excusable --- it also notes:
Scripture presents enough chronological information to estimate the number of years between Adam, whom God created on Day 6 of the creation week, and Christ, who was the last Adam. ... Adding these and other pieces, most of which even find confirmation from secular archaeological sources, brackets an age for the world of around 6,000 years.
Our Christian Against Science is also somewhat against their own Christian authorities here. But I'll let that slide since even the generally accepted creationist wrong answer is wrong by a factor of very nearly 1 million-fold (750,000 to be more precise).
Evidence of the Age of the Earth
Supposing you did want to come up with estimates of the age of the Earth, or the Universe, which one presumes that God dude might have made at roughly the same time, you could look at the history of scientific attempts to date the planet and cosmos.
By the 1790s, geologists were determining, based on fossils, sedimentation rates, and other evidence, with John Philips estimating that the Earth was at least 96 million years old, already far older than Ussher's Biblical chronology. Other scientific reckoning arrived at different numbers. Comte do Buffon looked at the rate of cooling of objects and tried to extrapolate to that of the Earth and arrived at an age of 75,000 years. That's over 1,000 times less than Smith's estimate, but still well over 10 times Ussher's. William Thomson, 1st Baron Kelvin also used thermodynamic arguments to estimate age at 20 million to 400 million years. (These rate-of-cooling estimates were made in ignorance of radioactivity and didn't account for the possibility of heat production within the Earth's interior, only one of several ways the discovery of radioactivity changed our understanding).
I'll skip over other 19th and early 20th century estimates to look at the model of plate tectonics, which became the central organising principle of geology only recently, being formally adopted in 1965, though it was first seriously proposed around 1915. The idea that "plates" constituting continents and ocean floors moved about over a liquid interior explains a tremendous amount of observed geological phenomena and evidence. The observable rates of movement, continental boundaries, similar geological formations, and similar fossil finds, also give us a timeframe for estimating an earlier supercontinent era of the Earth, characterised by a single large continent "Gondwana", about 180 million years ago. This need not have been the formation of the Earth, but it again points to an age far greater than Ussher's estimate.
The Earth is far more than 6,000 years old.
Evidence of the Age of the Universe
Looking outward we can determine distances to remote parts of the Universe based on several factors, two of the most notable of which are specific type of stars, and of the degree of red-shifting of light spectra which increases with distance.
Among the benchmark stars is one known as a Cepheid variable, which have a distinctive behaviour, changing in brightness in a characteristic manner and having a consistent absolute brightness. Another being Type 1A supernovae, also of characteristic brightness By noting the observed brightness of such stars, estimates of distances can be arrived at. Cepheids can be used to determine distances both within the Milky Way and to other galaxies. Supernovae can be seen across large portions of the visible Universe.
Redshift is the observed shift of atomic spectral emission and absorption bands such as in hydrogen and helium, both major constituents of stars, which increases with distance according to Hubble's Law. The greater the redshift, the greater the distance. And via redshift, we can directly observe distances of billions of light years. Since light travels at the rate of one light year per year, distance is also time, and so we're looking back in time billions of years. Again, the timeframes greatly exceed Ussher's increasingly troubled estimate.
We don't even have to call on Cepheids and redshift though.
Simple geometry, combined with modern telescope optics and precision, allow dynamical paralax estimates to be measured directly, by observing the apparent motion of "near" stars against the distant background. This is good to about 1,000 parsecs, or just a bit under 4,000 light years. Again, since looking further in distance is looking back in time, this means we're seeing relatively near regions of space which are roughly as distant, and as far back in time, as Ussher's estimate of the age of the entire Universe would be. Structures such as the Milky Way galaxy have an estimated diameter of 150,000 to 200,000 light years, with the largest galaxies being about 700,000 light hears in diameter. As before, space is time, and the implied ages of these structures greatly exceeds the Ussher chronology.
The Universe is far more than 6,000 years old.
Lead
Back to lead: Most of this is thought to have formed slowly in stars through what's called the s-process or r-process of neutron capture, in which lighter atomic nuclei acquire an additional neutron, or in "high neutron density environments" such as supernovae or neutron-star mergers. Lead occupies a position of stability within the nuclear potential curve, and so tends to be preferentially created. Again, whilst some lead on Earth is created through radioactive decay, most, probably more than 99% of it, was part of the initial planetary formation, having been initially created in stars, supernovae, or neutron-star collisions or mergers.
The period from about 1910 to 1965 was an extraordinary one for the understanding of Earth's geology. Nuclear chemistry and radioactivity gave new models for understanding and explaining phenomena, as did relativity and advances in astronomy. All collectively pointed to a far, far, far older world than even earlier scientific estimates had contemplated. Arthur Holmes made the first radiometric estimate in 1911, finding that tested rock samples were 1.6 billion years old. By 1927 the range was given as 1.6 to 3.0 billion years. Through the 1950s and 1960s, further estimates were based on terrestrial and extraterrestrial materials --- Earth-based rocks and meteorites, principally, but also returned Lunar samples. All converged on the 4.54 billion year +/- 1% range, suggesting a common formation of the entire Solar System.
One side-light of this work was the discovery of extensive lead contamination of virtually the entire laboratory used for this work in the 1950s, as well as any materials brought in from elsewhere. This was ultimately traced to the addition of lead to petrol in the US and elsewhere as an anti-knock formulation, and resulting in pervasive lead contamination of the environment, now thought to have had a major impact on health, cognitive development, mental health, and possibly criminal behaviour.
Geology and Creationism
That's only one of the intersections of geology, dating of the Earth, and the petrochemical industry. Fundamentalism, mentioned earlier, derives its name from The Fundamentals a series of books published between 1910 and 1915, by Lyman Stewart, the founder of Union Oil (later Unocal), and of Biola University, the Bible Institute of Los Angeles. Stewart was also responsible for introducing the use of field geologists into the practice of petroleum prospecting. Fundamentalism and Biola University have played major roles in advancing Young Earth Creationist myths and disinformation, whilst their founder and benefactor's own firm benefited from the applications of scientific geology.
Life is complicated.
But yeah: Earth is old. 4.54 billion +/- 1% years old.
Adapted from a comment posted here.
#Science #ScienceBitches #AccurateScienceIsBetterScience #AgeOfTheEarth #Lead #Creationism #Fundamentalism #LymanStewart #RedShift #CepheidVariables #RadiometricDating
