1) The first successful human heart transplant was performed by Dr. Christiaan Barnard in 1967.

2) The invention of the printing press by Johannes Gutenberg in the 15th century revolutionized the spread of knowledge and played a key role in the Renaissance.

3) Mount Kilimanjaro in Tanzania is the highest mountain in Africa and attracts climbers from around the world.

4) The smallest unit of time is known as a zeptosecond, which is equal to one trillionth of one billionth of a second.