You will hear a lecturer discussing marine archaeology and the technology used to investigate submerged sites.
First, you have some time to look at questions 31 to 40.
Now listen carefully and answer questions 31 to 40.
Today I want to introduce marine archaeology, the area of marine archaeology concerned with the ways people have interacted with oceans, lakes and rivers.
It examines vessels, their cargoes, harbour structures and other material remains.
I'll begin with one example, then explain how recent technology is changing this research.
Atlet Yam was a community on the eastern Mediterranean coast which appears to have prospered until roughly 7000 BC.
Its inhabitants raised cattle, fished and kept stores of grain.
They drew fresh water from wells and many stone houses were arranged around courtyards.
The village also had a remarkable monument, seven stones, each weighing about half a tonne set in a semicircle around a natural spring.
It may have served a ceremonial purpose.
Atlet Yam could have been overwhelmed suddenly by a tsunami or gradually flooded when a warmer climate melted glaciers and raised sea levels.
Whatever happened, the site now rests ten metres beneath the Mediterranean, covered by sand.
It has been called the largest and best preserved prehistoric settlement discovered on the seabed.
For marine archaeologists, the site offers an extraordinary amount of evidence.
By studying its buildings, tools and human remains, researchers have learned how this busy community operated and even identified illnesses suffered by some residents.
Yet one village provides only a narrow view of a vanished world.
A broader picture requires more submerged settlements and locating them is the real challenge.
In the past, divers had to search for wrecks and artefacts themselves.
During the second half of the 20th century, several kinds of underwater vehicle appeared.
Some were directed from a surface ship, while autonomous models could operate without a human controller.
Autonomous underwater vehicles, usually called AUVs, have long been used by the oil industry to produce maps of the seabed before rigs and pipelines are put in place.
They navigate with instruments such as compasses and sonar.
Until fairly recently, these machines cost a great deal and were so heavy that a winch on a large vessel was needed to lower them into the water.
Newer AUVs are far easier to handle and can be launched from the shore or a small boat.
Their lower price also puts them within reach of more research teams.
They are highly advanced as well.
Several vehicles can exchange information and decide, for example, how to divide a survey efficiently or locate particular objects.
Trials have shown that this cooperative method works.
In 2015, three AUVs searched for wrecks at Marsa Memi, near Sicily.
An ancient Roman ship lies there after sinking in the 6th century AD while transporting prefabricated pieces of marble intended for an early church.
The vehicles produced a detailed survey and detected other ships carrying columns made from the same material.
Establishing an underwater internet for AUVs is difficult, however.
Land-based Wi-Fi relies on electromagnetic waves which travel only a few centimetres through water.
A more complicated combination of methods is therefore necessary.
Light can carry data across short distances while acoustic waves are used over longer ones.
Researchers are also testing more inventive arrangements.
One vehicle working on the seabed can pass its data to another, which rises to the surface and sends the information to the team by satellite.
A further system lets AUVs exchange seabed scans and related data.
If one vehicle notices an unusual object, it can transmit the object's coordinates to a nearby AUV equipped with better cameras, so that the second machine can inspect it closely.
Marine archeologists see enormous possibilities in this technology.
One planned location for these vehicles is the Gulf of Berati, off Italy.
A Roman vessel about 2,000 years old was found there in 1974, at a depth of 18 metres.
It had been carrying medical supplies in containers made of wood or tin.
The cargo reveals treatments used at the time, including tablets that were probably dissolved to make a liquid for washing the eyes.
Other Roman ships sank close by with their loads and some contained enormous terracotta jars.
Some of those jars transported olive oil while others carried wine.
Often the containers are all that can still be seen because the wooden hulls lie buried beneath seabed silt.
Another project that's about to...
That is the end of part four.
You now have one minute to...
