Re: [dinosaur] Age of dinosaur fossils before radiometric dating

[Thomas Richard Holtz <tholtz@umd.edu>]

You should look into any history of geochronology: the story is long and interesting...

By the end of the 19th and earliest 20th Centuries, though, there were two main schools of thought. Many geologists and some biologists predicted the Earth was 100s of millions to billions of years old, mostly based on looking at contemporary rates of deposition and comparing them to the thickness of the physical geological column.

In contrast, some physicist (famously William Thomson, Lord Kelvin (of the temperature scale)) looked at the temperature profile of the Earth (and the temperature of the Sun), and assumed their heat was from an initial molten state or gravitational compression, respectively. With no new source of heat, the Earth could only be a few 10s of millions of years old at most. So the K/T (as it still was at the time) boundary was no more than 3 million years ago. Osborn happened to follow the Kelvin model.

The discovery of radioactivity both revealed a potential energy source to keep the Earth's interior warm AND the key to numerical dating of igneous rocks.

Here are a couple of books on the history of geochronology, but there are many more:

Richet & Venerella's 2009 A Natural History of Time

Jackson (or Wyse Jackson?) 2006 The Chronlogers Quest: The Search for the Age of the Earth

On Mon, Nov 13, 2017 at 9:49 AM, Poekilopleuron <dinosaurtom2015@seznam.cz> wrote:

Good day,

IÂve read that (for example) T. rex and Allosaurus fossils at the beginning of the 20th Century (prior to the first radiometric dating techniques) were "dated" at some 3-4 million years. I wonder how did scientists of those days (like Henry F. Osborn) figure out such estimates? Thank you in advance, Tom

--

Thomas R. Holtz, Jr.
Email:Âtholtz@umd.eduÂÂÂÂÂÂÂÂ Phone: 301-405-4084
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