The impact is thought to have happened in the Holocene period, around 3,500 years ago. The estimates of the age of the Kaali impact structure (Saaremaa Island, Estonia) provided by different authors vary by as much as 6,000 years, ranging from ~6,400 to ~400 years before current era (BCE). Analysis of silicate spherules in Estonian bogs show that the possible age of the impact craters could be approximately 7,600 years. A study based on elevated Ir signal in a nearby bog suggested much younger age of 4th century BC. The craters were formed by a meteor with an estimated impact velocity of between with a total mass of between 20 and 80 metric tonnes. According to some researchers the meteor arrived from the north-east.