Discover How We Came to Know the Cosmos

Chapter 6. The Age of the Universe

18th December 2017 by Dr Helen Klus

6.1 19th Century problems

The 1800s ended with a number of unresolved problems in physics. The Michelson-Morley experiment of 1887 (discussed in Book II) had shown that space is not filled with Aristotle’s aether, and that unlike everything else in the universe, the apparent speed of light is the same whether it’s travelling towards you or away from you.[1] This meant there was no explanation for how light can travel through space, since waves usually need a medium to travel in, and would have as yet unknown implications for the nature of space and time. Olbers’ paradox remained unsolved, as did the problem of explaining the shape of Mercury’s orbit (both discussed in Chapter 5), and people were increasingly worried about how long the Sun would continue to burn.

In the 17th century, English natural philosopher Isaac Newton had suggested that comets fuel the Sun, arguing that:

“...fixed stars that have been gradually wasted by the light and vapours emitted from them for a long time, may be recruited by comets that fall upon them; and from this fresh supply of new fuel these old stars, acquiring new splendour, may pass for new stars”.[2]

By the end of the 1800s, it had been suggested that the Sun could be fuelled by a chemical process, like combustion, yet even if the entire mass of the Sun were made of petrol, it would still only burn for about 7000 years.

This was not considered a problem in the 1700s, when the age of the Earth was accepted to be about 6000 years. This was based on Irish Bishop James Ussher’s argument that the world had been created on the 23rd of October 4004 BCE. Ussher had come to this conclusion by reading the bible and adding the male lineage from Adam through to Solomon. Beyond the time of Solomon, he cross-referenced the lineage of Kings with known historical data.[3] Yet by the end of the 1800s, there was evidence that the Earth must be at least 35,000 times older than this.

People had been discovering the fossilised remains of unknown animals for thousands of years, and these were often only found in specific strata - layers of sedimentary rock or soil. In the 1790s, British geologist William Smith suggested that different strata have different ages, where one layer of rock or soil forms over another. He argued that if the same fossils were found in strata at different locations, then the strata are probably the same age.[4]

British geologist John Phillips, used Smith’s theory to show that there must have been at least three major geological eras: the Palaeozoic (‘Age of Fishes’), the Mesozoic (‘Age of Reptiles’), and the Cenozoic (‘Age of Mammals’). Phillips estimated that the Earth could be up to 96 million years old.[5]

The lifetime of the Sun if it were fuelled by combustion:

Mass (m) = 2×1030 kg,

Energy emitted per second (L) = 3.9×1026 J/s, and

Energy released per kg burnt (HV) = 45×106 J/kg.

Rate of combustion (Rcom) = L/HV = 3.9×1026/45×106 = 8.7×1018 kg/s.

Lifetime = m/Rcom = 2×1030/8.7×1018 = 2.3×1011 s = 7,300 years.

Photograph of rock strata.

Figure 6.1
Image credit

Rock strata in the Petrified Forest National Park in Arizona. These were formed during the Triassic period over 200 million years ago.

The remains of extinct dinosaurs were first correctly identified in England in the early 1800s. The first belonged to the herbivorous Iguanodon, discovered in Sussex by palaeontologist Mary Ann Mantell in 1822.[6] The second was the carnivorous Megalosaurus, discovered in Oxford and identified by palaeontologist William Buckland in 1824,[7] and the third was the armoured Hylaeosaurus, also discovered in Sussex, and first identified by palaeontologist Gideon Mantell in 1833.[8]

Artist’s impression of an Iguanodon.

Figure 6.2
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Artist’s impressions of an Iguanodon, 1859 (no longer considered accurate).

Artist’s impression of a Megalosaurus.

Figure 6.3
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Artist’s impressions of a Megalosaurus, 1859 (no longer considered accurate).

Artist’s impression of a Hylaeosaurus.

Figure 6.4
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Artist’s impressions of a Hylaeosaurus, 1871 (no longer considered accurate).

British biologist and palaeontologist Richard Owen coined the term Dinosauria to encompass all three genera in 1842. Dinosauria is derived from the Greek words deinos, which is translated as ‘terrible, powerful or wondrous’ and the word sauros, which means ‘lizard’.[9]

In The Origin of Species, published in 1859, British naturalist Charles Darwin suggested that our current stage of evolution would require hundreds of millions of years.[10] British natural philosopher William Thomson, better known as Lord Kelvin, showed that it would take 20-40 million years for the Earth to cool to its current temperature from a molten state in 1897.[11]

In 1898, Darwin’s son, astronomer George Darwin, suggested that the Earth and Moon had once been part of the same molten mass but had broken apart. Astronomers now think that this occurred when it was hit by an object the size of Mars. George Darwin’s theory showed that it would take at least 56 million years for the Moon to become tidally locked with the Earth, so that we only see one side.[12]

Finally, in 1899, Irish physicist John Joly showed that it would take about 90 million years for the oceans to have accumulated their current salt content through mineral erosion.[13]

6.2 20th Century solutions

We now know that the Earth is about 4.54 billion years old. This was first determined by American geochemist Clair Cameron Patterson using the radioactive dating of meteorites in 1953.[14]

American astronomer Edwin Hubble estimated that the universe is about 9 billion years old in 1929.[15] Hubble’s calculations have since been refined to show that the universe is about 14 billion years old (discussed in Chapter 9).

The mystery of how the Sun is fuelled was solved in the early 1900s, with the discovery of nuclear fusion, which can fuel the Sun for about ten billion years (discussed in Chapter 11).

Olbers’ paradox would be resolved with the discovery of the big bang (discussed in Chapter 9), and the shape of Mercury’s orbit would be explained with German-Swiss-American physicist Albert Einstein’s theory of general relativity (discussed in Chapter 8).

The problems produced by the Michelson-Morley experiment would be resolved with quantum mechanics (discussed in Book II) and Einstein’s theory of special relativity (discussed in Chapter 7).

6.3 References

  1. Michelson, A. A., Morley, E. W., Sidereal Messenger 1887, 6, 306–310.

  2. Newton, I. in The Mathematical Principles of Natural Philosophy, translated by Motte, A., Daniel Adee, 1846 (1726).

  3. Fuller, J. G., Earth Sciences History 2005, 31, 5–14.

  4. Phillips, J. in Encyclopaedia Metropolitana: Or Universal Dictionary of Knowledge, (Eds.: Smedley, E., Rose, H. J., Rose, H. J.), B. Fellowes, 1845.

  5. Burchfield, J. D., Geological Society 1998, 143, 137–143.

  6. Mantell, G., Illustrations of the Geology of Sussex, Lupton Relfe, 1827.

  7. Buckland, W., Notice on the Megalosaurus Or Great Fossil Lizard of Stonesfield: From the Transactions of the Geological Society, Richard Taylor, 1824.

  8. Mantell, G., The geology of the south-east of England, Longman, Rees, Orme, Brown, Green and Longman, 1833.

  9. Owen, R., A Monograph on the Fossil Reptilia of the Wealden Formations, Cambridge University Press, 2015.

  10. Darwin, C., The Origin of Species, Project Gutenberg, 2009 (1859).

  11. Kwok, S., Stardust: The Cosmic Seeds of Life, Springer Science & Business Media, 2013.

  12. Chambers, J., Mitton, J., From Dust to Life: The Origin and Evolution of Our Solar System, Princeton University Press, 2013.

  13. Whitrow, G. J., What is Time?, Oxford University Press, 2003.

  14. Patterson, C. C., Proceedings of the Conference on Nuclear Processes in Geologic Settings 1953, 1, 36–44.

  15. Hubble, E., Proceedings of the National Academy of Sciences 1929, 15, 168–173.

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How We Came to Know the Cosmos: Space & Time

I Pre 20th Century theories

1. Constellations

2. Latitude and Longitude

3. Models of the Universe

4. Force, Momentum, and Energy

5. Newton’s theory of Gravity

6. The Age of the Universe

II 20th Century discoveries

7. Einstein’s theory of Special Relativity

8. Einstein’s theory of General Relativity

9. The Origin of the Universe

10. Galaxies

11. Stars

12. Red Giants and White Dwarfs

13. Supergiants, Supernova, and Neutron Stars

14. Black Holes

III Missions to planets

15. The planet Mercury

16. The planet Venus

17. The planet Earth

18. The Earth’s Moon

19. The planet Mars

20. The Asteroid Belt

21. The planet Jupiter

22. The planet Saturn

23. The planet Uranus

24. The planet Neptune

IV Beyond the planets

25. Comets

26. The Kuiper Belt and the Oort Cloud

27. The Pioneer and Voyager Missions

28. Discovering Exoplanets

29. The Search for Alien Life in the Universe

30. Where are all the Aliens?

V List of symbols

31. List of symbols

32. Image Copyright