Earth Sciences

Fossil Footprints

Some 385 million years ago, an early amphibian walked along a mud flat while the tide was out. The footprints it made in wet sand later turned to stone. The tracks were discovered in 1992 by a Swiss geologist on Valentia Island off Co Kerry. The creature resembled a salamander and lived partly on land and partly in water. It was about one metre long and waddled like a crocodile.

Image: Courtesy of the Geological Survey of Ireland

Fossil Footprints
Image: Courtesy of the Geological Survey of Ireland

Fossil Footprints

Some 385 million years ago, an early amphibian walked along a mud flat while the tide was out. The footprints it made in wet sand later turned to stone. The tracks were discovered in 1992 by a Swiss geologist on Valentia Island off Co Kerry. The creature resembled a salamander and lived partly on land and partly in water. It was about one metre long and waddled like a crocodile.

Image: Courtesy of the Geological Survey of Ireland

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The Age of the Earth

Dublin-born James Ussher counted the generations in the Old Testament, consulted ancient Egyptian and Hebrew texts and calendars and concluded that the world began on October 23rd 4004 BC. Other scholars calculated similar dates, but Ussher's was the one that was widely accepted. In the 19th century, scientists tried other ways of calculating an age: based on the amount of salt that had accumulated in the oceans, for instance, or the time it had taken the Earth to cool from a molten ball to a solid planet. Some techniques were useful, others were flawed. The discovery of radioactivity in the early 20th century provided new ways of dating rocks accurately. We now know our planet is 4.6 billion years old. Irish scientists who made important contributions to this work in the 19th century were geologists Samuel Haughton and John Joly and physicist William Thompson (Lord Kelvin).

Image: James Ussher (1581-1656)

The Age of the Earth
Image: James Ussher (1581-1656)

The Age of the Earth

Dublin-born James Ussher counted the generations in the Old Testament, consulted ancient Egyptian and Hebrew texts and calendars and concluded that the world began on October 23rd 4004 BC. Other scholars calculated similar dates, but Ussher's was the one that was widely accepted. In the 19th century, scientists tried other ways of calculating an age: based on the amount of salt that had accumulated in the oceans, for instance, or the time it had taken the Earth to cool from a molten ball to a solid planet. Some techniques were useful, others were flawed. The discovery of radioactivity in the early 20th century provided new ways of dating rocks accurately. We now know our planet is 4.6 billion years old. Irish scientists who made important contributions to this work in the 19th century were geologists Samuel Haughton and John Joly and physicist William Thompson (Lord Kelvin).

Image: James Ussher (1581-1656)

Enlarge image

Over the past 100 years, earth scientists have pieced together the story of Ireland's landscape. They identified the seam that runs from Limerick to Louth, marking the place where two ancient continents collided 400 million years ago. (See the Physical Landscape feature)

They located the oldest place in Ireland: Inishtrahull, a small rocky island off Donegal is zircon-dated at 1.778 billion years old. And they found the oldest fossil footprints in the northern hemisphere on Valentia Island, made 385 million years ago by a primitive four-legged creature. Several other Irish fossils turned out to be internationally important.

Irish scientists in turn have added to our understanding of geology and the world around us. Many contributed to estimates of the Age of the Earth, starting with Archbishop James Ussher who in the 1650s calculated that the Earth was 6,000 years old, and ending with John Joly, who was one of the first to use radioactivity to date rock in the early 1900s.

Even from the earliest Stone Age times, geology has been intimately linked with economic development. Every resource we use was either grown, or dug from the ground. Some 6000 years ago Stone Age people found the ideal stone for making stone axes: a porcellanite on Rathlin Island. Axes made at a 'factory' there were traded across Europe.

In the early Bronze Age 4,500 years ago, metals became important. Bronze Age miners found useful copper sources in Co Kerry, and the oldest-known copper mine in northwest Europe is at Ross Island near Killarney. In the centuries since, prospectors have found dozens of different minerals in Ireland, including commercial deposits of lead, silver, copper, uranium, natural gas and especially zinc.