The Lappajärvi impact structure is estimated to be 77.85 ± 0.78 million years old (Campanian age of the Late Cretaceous time period).

[8] According to current estimates, it is believed to have been formed during the intensified meteorite and asteroid bombardment in the Late Cretaceous epoch.

Kärnänsaari has been suspected to be the central uplift of the impact crater, although it could also be a mere erosional remnant shaped by glacial activity.

[12] Typical rocks found in meteorite craters, such as breccia, as well as impact diamonds and minerals like suevite and coesite, have been discovered in Lappajärvi.

[22] In 1967, Martti Lehtinen started his investigations of the crater and discovered suevite in the Hietakangas gravel pits in July 1967.

[23] In 1976, Lehtinen published an English-language doctoral dissertation on the meteorite theory, which included evidence of quartz transformations in certain rock samples that could not have resulted from volcanic activity.

[24] Gravity measurements conducted in the same year also supported the meteorite theory, as a gravitational anomaly was detected within a 17-kilometer diameter area.

[25] In 1980, German researchers Elmar Jessberger and Uwe Reimold used the argon–argon dating method to determine the age of the crater to be approximately 77.3 million years.

[30] The fourth drilling reached a depth of 275 meters in the intermediate island between Kärnänsaari and Matalasaari, but no kärnäite was found.