Magnesium (Mg) naturally occurs in three stable isotopes, 24 Mg, 25 Mg, and 26 Mg. There are 19 radioisotopes that have been discovered, ranging from 19 Mg to 40 Mg. The longest-lived radioisotope is 28 Mg with a half-life of 20.915 hours. The lighter isotopes mostly decay to isotopes of sodium while the heavier isotopes decay to isotopes of aluminium. The shortest-lived is 39 Mg with a half-life shorter than 180 nanoseconds, or possibly 40 Mg, with a half-life longer than 170 nanoseconds (the half-life of 19 Mg is unknown). Standard atomic mass: 24.3050(6) u. A chart showing the abundances of the naturally-occurring isotopes of magnesium.
Another large shark, capable of growing to a length of over 16 feet, or 5 meters, the Tiger Shark can be found in the Caribbean and other warm waters around the world. They can have a blue to light green colour, combined with a white or light yellow belly.
The bull shark, also known as the Zambezi shark in Africa, and Lake Nicaragua shark in Nicaragua, is a requiem shark commonly found worldwide in warm, shallow waters along coasts and in rivers. The bull shark is known for its aggressive nature, predilection for warm shallow water, and presence in brackish and freshwater systems including estuaries and rivers. Bull sharks can thrive in both salt and fresh water and can travel far up rivers. They have been known to travel up the Mississippi River as far as Alton, Illinois, about 700 miles (1100 km) from the ocean.