Human life on the Korean Peninsula can be traced as far back as 30,000BC, to the Paleolithic period, and physical artifacts have been dated as early as 20,825B. Physical artifacts become more common in the neolithic period (around 4000BC). It is believed at this time the early Koreans became more sedentary, and switched from being nomadic hunter-gatherers to an agricultural society, there is also evidence that animals had been domesticated by this time.
Common artifacts of this time include stone knives and axes, as well as other tools crafted form bone and stone. Early pottery has also been discovered in the form of bowls, vases and dishes. Little is known about these early koreans that has not been clouded by myth and legend. It is not until the bronze age that a clearer picture of early Korean civilization can be detailed.
By the bronze age Koreans had developed their own style of architecture, in the form of dolmens. Dolmens are a prehistoric monument made of a large flat slab of stone laid across upright stones (think stonehenge). Stone implements found in the proximity of these dolmen sites confirm that the peoples of this era were settled agriculturalists. The Bronze Age provides evidence that the Chinese culture penetrated the Korean region well before the fifth century BC, metallic artifacts similar to chinese designs from the same era are offered as proof.
In the Iron age (~300 BC) southern Korea began to engage in trade with China and Japan, it is thought that the secrets of iron working were brought to Korea from one of these lands. Weapons became more practical due to these innovations and would be instrumental into ushering in the era known to Koreans as "The Three Kingdoms Period".
Credit given to USC Berkley Korean history Project