There are plenty of secrets inside Parliament House. But how about underneath it?
Down the lifts, through the labyrinth of service corridors and behind an innocuous door lies evidence of the Canberra region more than 400 million years ago. Back then, the area was covered by ocean, volcanoes were spewing lava and tectonic forces were creating mountains.
Incredibly, an ancient rock formation from that time remains intact beneath Parliament House, once thought to have been destroyed in the construction of the building 35 years ago but, conversely, actually preserved by virtue of it being hidden beneath a high-security facility.
What makes the rock beneath Parliament House even more intriguing is it reveals a phenomenon known as "unconformity"; in this case where one layer of rock is 435 million years old and the next is 425 million. What happened to remove 10 million years' worth of rock history?
For National Science Week (August 12 - 20), special tours of the Parliament House unconformity will be conducted by Geoscience Australia's chief scientist Dr Steve Hill, giving a rare insight into something far more dramatic than Question Time.
Geoscience's education centre coordinator Joe Fayle, also a geologist, says the formation was discovered in about 1995 through a chance conversation between a visitor guide at Parliament House and a local geologist Wolf Mayer. The guide told him there were in fact rocks still underneath the building. Professor Mayer went straight down to see for himself and was astounded by the find.
What he found revealed the beginnings of the land that became Canberra.
Mr Fayle said during the Silurian period (from around 444 million years ago to 419 million years ago), the ACT was still under water and large amounts of sediment were being washed into the ancient ocean.
That sediment came to form what is known as the Black Mountain sandstone, thought to be 435 million years old and one of the layers of rock beneath Parliament House.
"In geology, we expect rocks to go up in age-sequence and be conformable, meaning the older layers are at the bottom, the younger ones are at the top without any gaps" Mr Fayle said.
"But in this particular case, we have gap in the sequence where we have a different rock type, called the Camp Hill sandstone, sitting on the top of the Black Mountain sandstone and that Camp Hill sandstone is 425 million years old which means the point at which they touch we have no record of about 10 million years of Earth's history."
Mr Fayle said that meant, if geologists read rocks like a book of history, the formation beneath Parliament House was missing a page.
This is probably a result of a combination of forces - tectonic movement pushing up rock from the sea floor forming mountains, followed by extensive erosion removing that page of Earth's history.
Mr Fayle said the Parliament House unconformity was a "very special and important" glimpse into Canberra's ancient past.
The Unconformity Geology Tours will take place on Friday, August 11 and Saturday, August 12 at Parliament House. The one-hour tours will be at 5.30pm, 6pm and 6.30pm on August 11 and 2pm, 2.30pm and 3pm on August 12.
The cost is $76 for adults and $56 for concession card holders.
They can be booked at aph.gov.au/Visit_Parliament.
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