The top options were chosen by an expert committee of geoscientists, palaeontologists, and science communicators.

"Fossils instil a sense of wonder about time and place, particularly about the incredible scale of geological time and the many changes to our region," Geoscience Australia chief scientist Steve Hill said.

"All of our ACT fossil emblem candidates are marine invertebrates which clearly brings home how different Canberra was millions of years ago."

Voting opened on Monday with five finalists including a graptolite, two trilobites and two brachiopods.

Each one comes from a different part of the ACT and are about 430 million years old.

The first candidate is Retziella capricorniae, a brachiopod found in Queensland, NSW and the ACT.

The second is Monograptus exiguus, a graptolite important to the Canberra region as it allows scientists to date the State Circle shale back to the early Silurian.

A trilobite hailing from Coppins Crossing, Apocalymene coppinsensis is the third choice. The original discovery site of this fossil has been covered by the lower Molonglo wastewater treatment site.

The second brachiopod was named Atrypa duntroonensis, after the location it was found, at Woolshed Creek near Duntroon. It is the most abundant and complete brachiopod fossil in the ACT.

The final option is the most common trilobite in the ACT, Batocara mitchelli. It is usually found in fragments but an almost complete fossil was discovered during the drilling of foundations of the John Gorton Building, bits have also been found during Braddon's redevelopment.

The fossil emblem would join the ACT's other emblems the royal bluebell, gang-gang cockatoo and Southern brush-tailed rock-wallaby.

The ACT would become the fourth Australian jurisdiction with a fossil emblem, following NSW, Western Australia and South Australia.

Voting closes during National Science Week, on October 13.