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The origins of life
In Search of Deep Time
The beginnings of a scientific approach
Edmund Halley (1715) began a trend of observations made in nature used to determine the age of the Earth. The passage of comets, eclipses and the precession of stars through constellations were being considered more valid than biblical references.
George-Louis Leclerc de Buffon (director of the Jardin du Roi) proposed that the Earth was formed as a molten lump (caused by a collision between a comet and the early sun). As a molten planet spins its equator bulges and the poles flatten. The bulge in the Earth's equator was determined by differences in gravitation between the poles and the equator. This was determined by the differences in the time kept by pendulum clocks at the equator and at high latitudes. The time to cool down and solidify could be used to establish the age of the Earth but he thought that the Earth had finally solidified long ago.
In 1765 it was discovered that the Earth is still molten inside, Buffon's idea was still valid. So he proceeded to experiment with iron balls of different dimensions and time how long they took to cool down. He discovered that there was a direct relationship between cooling and diameter of the ball. These data were then scaled up to the size of the Earth. His estimate was 74832 years.
Geology verses Physics
Patrick Brydone (1773) observing lava flows from Etna was told by a local historian that it took about 2000 years for the lava to be covered by a layer of soil. In digging a pit 7 layers of lava flows were discovered putting Etna's age at 14000 years.
James Hutton (1785) interested in soil formation for farming purposes developed the idea of the rock cycle. That is the planet's surface is continually being eroded down but the rocks are also being uplifted by earth movements building up new mountain ranges.
George Cuvier (1812) discovered that each layer of rock had its characteristic layer of fossils. This led to a relative method of dating fossils.
Charles Lyell (1828) observed that 18% of fossils of tertiary rock were present today.
If the extinction rate was uniform for all geological periods an estimate could be made of the age of rocks, but it would still be relative as there is no way of calibrating it.
(Lyell developed this hypothesis from his idea of uniformitarianism - that is, the same forces were acting on the earth in the past as they are now.)
Charles Darwin (1859) observed that the evolution of new species was a slow process. His theory of natural selection needed a long time. He calculated rates of erosion and put the origin of the Earth at more than 300 million years. After his calculations were shown to have an error, the estimate was revised back to 96 million years. Darwin admitted was not long enough to account for the evolution of species.
Lord Kelvin (of Kelvin temperature scale) was an antievolutionist. He used the cooling of the Earth again, with more precise temperature data, to estimate the age of the Earth. His estimate came to 98 million years.
Other estimates based on different calculations seemed to support him.
The credibility of evolution suffered.
Physics to the rescue
The discovery of radioactivity by Henri Becquerel (1896) changed everything. Pierre and Marie Curie showed that the energy released by radioactivity did not change with variations in temperature or pressure.
Lord Kelvin's calculation was shown to be false when in 1904 it was discovered that the Earth generates heat through radioactivity. In 1902 Ernest Rutherford and Frederick Soddy discovered that radioactivity accompanied the disintegration of atoms into other atoms particles leading in 1905 to the development of a natural chronometer radioactive decay.
Initial estimates put the origin of the Earth back to 570 million years.
By 1907 this was pushed back to 2200 million years.
In 1929 geophysicists had pushed the origin of the Earth back to 3.4 billion years.
Light years behind
Ole Rømer (1676) discovered that light had a speed whilst observing the movement of the moons around Jupiter.
Henrietta Leavitt (1912) discovered stars whose brightness varied at a constant rate. This gave a relative unit of distance for astronomy. Edwin Hubble 1919 measured the galaxy as being 300 000 light years across and by 1923 he had estimated the Andromeda Nebula to be 10 million light years away.
By 1931 observations of the furthest stars put the age of the universe at 1.8 billion years which was, apparently, not as old as the rock on Earth!
Better measurements lead to an estimate of 3.6 billion years by 1952. Meanwhile the use of the uranium-lead disintegration from pieces of meteorite put the age of the Earth at 4.5 billion years. Close but not close enough.
Light years ahead
By the end of the century the data from the Hubble orbiting telescope and much improved computing power of the astrophysicists has put the age of the Universe at 13.4 billion years (The Big Bang).
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