Geysers are one type of hydrothermal vents. They gush hot water from deep underground.
Oceanographers found hydrothermal vents at the bottom of the ocean gushing hot water at more than 400 ºC.
A vent site in the Cayman Trough named Beebe, which is the world's deepest known hydrothermal site at ~5,000 m (16,000 ft) below sea level, has shown sustained supercritical venting at 401 ºC (754 ºF) and 2.3 wt% NaCl.
1400 years ago people could only have seen geysers at the surface but nobody could have seen this at the bottom of the ocean. However the Quran says that the oceans are being heated.
Sujirat "سُجِّرَتْ " in Arabic means heated. Well is 400 ºC hot enough?
How could an illiterate man who lived 1400 years ago have known that oceans are being heated?
The Quran (Koran, the book of Islam) contains scientific knowledge that could not have been known 1400 years ago. It ranges from basic arithmetics to the most advanced topics in astrophysics. You are invited to go through those miracles and judge for yourself.