Along the middle length of the desert there are a number of raised, hardened areas of calcium carbonate, gypsum, marl, or clay that were once the site of shallow lakes.
These lakes existed during periods from 6,000 to 5,000 years ago and 3,000 to 2,000 years ago.
the Banu Yam and Banu Hamdan (in Yemen and the Najran region of southern Saudi Arabia), and the Bani Yas (in the United Arab Emirates).
A few road links connect these tribal settlements to the area's water resources and oil production centers.
The rule of the Imams in Oman began in the eighth century when Al-Julanda bin Masood was elected as the first Imam in 751AD and his reign lasted intermittently for four centuries until 1154 AD.
The Nabhani dynasty took control of Oman 1154 AD and the Nabhani kings ruled Oman for four and a half centuries.
Desertification has increased through the millennia. Before desertification made the caravan trails leading across the Rub' al Khali so difficult, the caravans of the frankincense trade crossed now virtually impassable stretches of wasteland, until about AD 300.
Ghawar, the largest oil field in the world, extends southward into the northernmost parts of the Empty Quarter.The expedition consisted of 89 environmentalists, geologists and scientists from Saudi Arabia and abroad.Various types of fossilized creatures as well as meteorites were discovered in the desert.Evidence suggests that the lakes were home to a variety of flora and fauna.
Fossil remains indicate the presence of several animal species, such as hippopotamus, water buffalo, and long-horned cattle.
It seems likely that at this time Sohar was one of the largest and most important cities in the Arab world.