Short answers, pulled from the story.
The oldest known hammer was discovered in 2012 by Sonia Harmand and Jason Lewis of Stony Brook University near Lake Turkana in Kenya. This ancient tool dates back 3.3 million years and was found in a deposit alongside other rocks used to strike wood, bone, or other stones. The archaeological record suggests this may be the oldest tool for which definite evidence exists.
The modern hammer head is typically made of steel that has been heat treated for hardness. The handle, known as a haft or helve, is traditionally crafted from wood such as hickory or ash, or from plastic and rigid fiberglass resin. Some hammers are one-piece designs made mostly of a single material with the handle coated or wrapped in resilient material such as rubber for improved grip.
There are over 40 different types of hammers, each shaped and sized for specific purposes ranging from carpentry to blacksmithing. Common examples include the claw hammer used in framing, the ball-peen hammer used by blacksmiths, and the sledgehammer used in open spaces. Specialized tools include the geologist's hammer, the engineer's hammer, and the gavel used by judges.
Hitting one's fingertip with a hammer can cause a comminuted fracture of the finger and uncontrolled shock waves can injure nerves and the skeleton. Awkward handles can cause repetitive stress injury to hand and arm joints, and striking metal objects may produce small metallic projectiles which can become lodged in the eye. Both manual and powered hammers can cause peripheral neuropathy or a variety of other ailments when used improperly.
The Norse god of thunder and lightning Thor wielded a hammer named Mjölnir, and the Greek hero Hercules was associated with the tool. The god Sucellus carried a hammer in Celtic and Gallo-Roman lore, while the hammer of John Henry appears in American folklore. Judah Maccabee was nicknamed The Hammer, possibly in recognition of his ferocity in battle.
The hammer and sickle became the symbol of the former Soviet Union, strongly linked to communism and early socialism. The hammer is used in some coats of arms in former socialist countries like East Germany, and a variant known as the Hammer and Sword symbolizes Strasserism. The Workers' Party of Korea incorporated an ink brush on the middle of their hammer symbol, which represents both Juche and Songun ideologies.