This timeline provides a look at some of the historical aspects in finding out the age of the Earth. Find about more the developments in how geologists find out the ages of rocks and fossils.
1860 – Earth ancient, but no date
Many geologists have evidence that Earth is ancient but cannot give an actual date as they only have relative dating methods. Some still use the Bible and other religious texts to support the idea that Earth is only about 6,000 years old.
1862 – Earth 100 million years old
William Thomson (later called Lord Kelvin) estimates the Earth is 100 million years old, based on its cooling from a very hot creation. He is a long way out, because he does not know about the heat from natural radioactivity.
1896 – Radioactivity discovered
Antoine Henri Becquerel discovers the radioactivity of uranium. The actual term ‘radioactivity’ is not used until 2 years later by Marie and Pierre Curie.
1902 – Radioactive decay
Ernest Rutherford and Frederick Soddy work out the cause and nature of radioactive decay.
1903 – Heat from radioactivity
George Darwin and John Joly point out that the newly discovered heat from radioactivity in rocks would upset earlier assumptions about the scientific age of the Earth.
1905 – A way to date rocks
Ernest Rutherford suggests that it should be possible to use radioactive elements with long half-lives, such as uranium, to work out the ages of rocks.
1907 – A new age for Earth
Bertram Boltwood uses the ratios of uranium and its decay product, lead, in rocks to suggest dates of 92–570 million years.
1911 – Even earlier dates
Arthur Holmes improves on Boltwood’s work. Rock determined to be Carboniferous by relative dating is 340 million years old, a Precambrian rock is 1,640 million years old. These dates are not widely accepted, as they disagree with earlier dating methods.
1920 – Mass spectrometer
Francis Aston invents the mass spectrometer for studying isotopes, which have only been known about for a few years.
1927 – Not the oldest rocks
Arthur Holmes suggests that Earth is 1.6–3 billion years old. He realises that all the rocks being chemically dated were formed a long time after Earth was first formed.
1941 – 3.2 billion years old
EK Gerling estimates the age of the Earth as 3.2 billion years. He bases this on rocks he thinks are from the time when Earth was formed. These rocks are later shown to come from after Earth’s formation.
1946 – A better instrument
Alfred Nier improves the mass spectrometer, making it easier for geologists around the world to measure isotopes.
1950 – Looking for oldest rocks
By now, isotope dating has become fairly precise. There is still a problem finding rocks from the earliest formation of Earth, as they have mostly been reworked through the rock cycle.
1956 – Meteorites
Clair Patterson realises that some meteorites were formed at the same time as the Earth and have stayed unchanged. He gets the age of 4.55 ± 0.3 billion years from the Canyon Diablo meteorite.
1972 – Moon rock
The oldest rocks brought back from the Moon by the Apollo 17 mission have radiometric dates of up to 4.5 billion years. It is thought that the Moon formed at a similar time to Earth.
1983 -–Oldest crystals
Zircon crystals in Western Australia are dated to 4.2 billion years old. The zircon has now become part of younger rocks but has not changed since it was first formed.
2007 – Oldest Earth rocks
The oldest known rocks, called Acasta gneiss, are found in Canada, dated at 4.03 billion years old. The 1983 Australian crystals are older, but are no longer in their original rock.
2010 – Improved error range
Many meteorites have now been dated, improving Patterson’s 1956 age of the Earth of 4.55 ± 0.3 billion years to 4.55 ± 0.02 billion years. This reduction in error means that geologists have become more confident in their estimates of the age of the Earth.
Use Developing the New Zealand geological timescale to learn about how geologists have built up an international timescale of Earth’s history, based on relative and absolute dating methods. New Zealand scientists have added to this to reflect the country’s unique history.
Help your students understand more about timescales, big numbers and different dating methods with one of these activities below:
Build a timescale – develop a timescale for a person’s life. The techniques of relative and absolute dating are similar to those used in the construction of a geological timescale.
Big numbers in science – investigate the use of big numbers, such as millions and billions, and they encounter ways to understand what these big numbers mean.