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 true statements about the cosmic microwave background radiation

2points what is the term for a female reproductive cell? a. egg b. chromatid c. allele d. fertilization

8) animals respond in various ways to stimuli detected through their senses. some of these responses are stimulated by the presence of danger. which of these animal responses is the best example of a response to an immediate threat? a) a rooster crows every morning at the first sign of light. b) as something approaches an octopus, it shoots a cloud of ink. c) from late fall until spring, bears hibernate to preserve energy. d) a dog is getting hot in the sunlight, so he moves to a shaded area.