However, some reefs were destroyed in the Persian Gulf, mostly caused by phosphate water pollution and resultant increase in algae growth as well as oil pollution from ships and pipeline leakage. The fertile soils of Yemen have encouraged settlement of almost all of the land from sea level up to the mountains at . In the higher elevations, elaborate terraces have been constructed to facilitate grain, fruit, coffee, ginger and khat cultivation. The Arabian peninsula is known for its rich oil, i.e. petroleum production due to its geographical location. History Stone tools from the Middle Paleolithic age along with fossils of other animals discovered at Ti's al Ghadah, in northwestern Saudi Arabia, might imply that hominins migrated through a "Green Arabia" between 300,000 and 500,000 years ago. 200,000-year-old stone tools were discovered at Shuaib Al-Adgham in the eastern Al-Qassim Province, which would indicate that many prehistoric sites, located along a network of rivers, had once existed in the area. Acheulean tools found in Saffaqah, Riyadh Region reveal that hominins lived in the Arabian Peninsula around 188,000 years ago. Human habitation in Arabia may have occurred as early as 130,000 years ago. A fossilized Homo sapiens finger bone found at Al Wusta in the Nefud Desert dates to approximately 90,000 years ago and is the oldest human fossil discovered outside of Africa and the Levant. This indicates human migrations from Africa to Arabia occurred around this time. Pre-Islamic Arabia There is evidence that human habitation in the Arabian Peninsula dates back to about 106,000 to 130,000 years ago. The harsh climate historically prevented much settlement in the pre-Islamic Arabian peninsula, apart from a small number of urban trading settlements, such as Mecca and Medina, located in the Hejaz in the west of the peninsula. Archaeology has revealed the existence of many civilizations in pre-Islamic Arabia (such as the Thamud), especially in South Arabia. South Arabian civilizations include the Sheba, the Himyarite Kingdom, the Kingdom of Awsan, the Kingdom of Ma'īn and the Sabaean Kingdom. From 106 AD to 630 AD northwestern Arabia was under the control of the Roman Empire, which renamed it Arabia Petraea. Central Arabia was the location of the Kingdom of Kinda in the 4th, 5th and early 6th centuries. Eastern Arabia was home to the Dilmun civilization. The earliest known events in Arabian history are migrations from the peninsula into neighbouring areas. The Arabian peninsula has long