"There is a line that starts in northeastern Washington and then travels approximately along the border of Washington and Idaho and the border of Oregon and Idaho. This line separates two areas that have different values of Strontium 87. Strontium 87 is an isotope that is stable, meaning it is no longer radioactive. Its parent material is Rubidium 87. Rocks east of this line have a much higher concentration of Strontium 87, while rocks west of this line have a low concentration of Strontium 87. Explain why this occurs."

so you know what happened be fore you were alive

explanation:

can you explain it better

european feudalism was a combination of legal and military customs in medieval europe that flourished between the 9th and 15th centuries. broadly defined, it was a way of structuring society around relationships derived from the holding of land in exchange for service or labour.

japanese feudalism. the era of feudalism in japan took place from the 12th through 19th centuries. during that period local rulers, either powerful families or military warlords, dominated the land, while the emperor was merely a figurehead and not a significant political presence.