Mari Tõrv, associate professor of archaeology at the University of Tartu, told ERR's Novaator portal that human bones are generally quite well preserved given Estonia's climate and soil types, so construction projects simply have to take this inevitability into account.

Tõrv said several factors affect the preservation of bones in the soil.

The most important is the immediate environment in which the remains are situated, including groundwater, the above ground climate, and soil acidity or pH.

The nature of burial of the remains, which reflect customs of the time, can also be factors in how well bones are preserved.

"Bones certainly survive better in cold environments or, conversely, in hot and dry conditions," she added.

As for pH levels, Tõrv stressed that alkaline soils help to preserve bones much better than acidic soils.

She said: "An acidic environment, as it were eats away at the bone over time."

"How quickly this will happen depends on the specific environment, and how the remains were interred," Tõrv added.

At the same time, bones do not always deteriorate at all. Their structure can be preserved for thousands or even millions of years, if and when fossilization occurs.

Tõrv said: "A bone is like a sponge, one whose chemical composition changes in the ground. During fossilization, soil and groundwater wash out the organic particles in the bone and replace them with tiny mineral particles found in the soil," explaining how fossilization works.

"Thanks to fossils, we know a lot about the Earth's very distant history," Tõrv added.

Bogs preserve bodies well, but without bones

Estonia is well-known for its vast areas of bog and marsh.

These, as is seen in other parts of Europe, present ideal conditions for preserving corpses.

The downside of this is that bones generally do not last in boggy conditions.

"The cold, acidic, and oxygen-limited environment of bogs preserves soft tissue, such as skin and internal organs, very well."

"However, this environment breaks down the mineral component of the bones and also leaches out organic matter. As a result, many bog bodies do not have intact, preserved bones, or instead they have become softer over the centuries," Tõrv continued.

According to Tõrv, it is extracting the organic portion, namely collagen, of well-preserved, millennia-old bones, is viable.

By analyzing its chemical composition, conclusions can be drawn about the diet and health of our antecedents, Tõrv noted.

"In the case of bog bodies, however, the organic portion of the bone has generally already disappeared from the skeleton."

In terms of DNA, it is now feasible to in effect travel back in time over 400,000 years.

The oldest DNA sequence identified derives from the remains not of our species, homo sapiens sapiens, but of a Neanderthal, H. sapiens neanderthalensis, found in the Atapuerca mountains of northern Spain.

This find demonstrates that bones can remain preserved for a very long period of time yet without fossilizing, given the right conditions.

The oldest human bones found in Estonia to date are about 8,500 years old.

"This does not mean that older bones could not be preserved here; simply that our oldest traces of human settlement date back 11,000 years," she continued.

The oldest known Estonian settlement, Pulli on the banks of the Pärnu River, has yielded finds such as animal and fish bones have as food remnants.

The oldest bones of any kind found preserved in Estonia belonged to wooly mammoths and are around 40,000 years old, Tõrv noted.

So if settlements in Estonia date back so far, why haven't human remains from that era been found? According to the archaeologist, the answer lies in burial customs. "We do not have archaeologically preserved burials from the early hunter-gatherers," Tõrv said.

"As archaeologists, we can only study burials if they have actually been buried. Perhaps the early hunters-gatherers left their deceased on the surface of the ground instead? This does not mean they did not honor family members; rather, their customs were simply different. That we have not yet found the oldest burial sites is also possible," she went on.

Bones in Estonia often better preserved than in other neighboring northern countries

The oldest bones found in Estonia come from the headland of the Narva River valley, near the present-day Narva fortress, and were from a Stone Age settlement. "From that same area, near Narva Jõesuu, scientists found in the 2010s burials from a Corded Ware culture settlement, dating back 5,000–4,500 years."

"However, the burial environment there was so acidic and oxygen-rich that it allowed bacteria and fungi to do their work in such a way that almost no bones were preserved," Tõrv added.

"Only tooth enamel, which is our strongest bone tissue, remained. So, the preservation of bones depends greatly on the local burial environment."

To sum up, Tõrv estimates that bones preserve well in Estonia.

"We have a relatively cold climate and a generally alkaline soil, which preserves bone tissue. This likely also indicates that burial sites, perhaps unintentionally, have been chosen at various points in history to indeed be at locations favorable for bone preservation. If we take the skeleton found on Kunderi tänav as an example, we see that remains from burials dating to the 17th century are predominantly very well preserved," she added.

In Finland, however, the picture is completely different. "There, the soil is significantly more acidic, and skeletons are rarely well-preserved. From the stone ages, for instance, only burial pits with some stained soil and grave goods remain, but not the bones themselves.

"This applies not only to the stone ages, but to all later periods too. Finding human remains in Finland is a rather rare occurrence," she added. "

In Estonia, when carrying out excavation work in cities of medieval or early modern origin—whether for constructing a new building or repairing existing infrastructure— the likelihood of encountering a cemetery or other burial site has to be factored in, Tõrv said.

"We have a societal compact that we will not destroy these skeletons with an excavator or move the soil heap carelessly to another site. Instead, the human remains must be carefully excavated and documented, in the course of archaeological fieldwork. After that fieldwork, the remains can be analyzed, to tell the stories of our collective past, and they are later re-interred."

--

Follow ERR News on Facebook and Twitter and never miss an update!