3- Considera os seguintes isótopos radioativos e os respetivos tempos de semivida: Isótopo pai Isótopo filho Semivida (anos)
40K 40Ar 1,4x109
235U 207Pb 0,7x109

3.1.1- Foi feita a análise da desintegração de átomos de 40K contidos em minerais de uma amostra de rocha, tendo-se verificado que a desintegração se iniciou há 2,8x109 anos. Indica, justificando com todos os cálculos, a percentagem de átomos de 40Ar existentes nessa amostra de rocha.

(select all the correct choose each statement that is scientific. - the opinions of randomly selected participants in a survey prove the idea that global temperatures are not increasing on earth. - the universe's average temperature and rate of expansion support the idea that it began as one super-dense and hot mass 13.8 billion years ago. - ocean tides are caused by the uneven gravitational pulls of the moon and sun on different parts of earth. - human life is more valuable than other forms of life on earth because humans are more intelligent than other organisms.

To confirm when to exclude children from school it’s recommended that you refer to guidelines from which of the following organizations

They live on every continent except antarctica