Explanation:
waterfalls are temporary features of rivers because stream erosion is greatest at waterfalls and rapids. The water that falls at the base of the waterfall erodes rock there, leaving the rock at the tops of the waterfalls to overhang. Overall, undermining causes waterfalls to recede farther upstream.
Answer: Igneous Rock
Explanation: Radiometric dating is used to date rocks by measuring the decay of their composite materials. Stable isotopes remain the same over time while the nucleus of an unstable or radioactive isotope will decay to form other isotopes
.
Dating rocks using Isotopic methods uses the decay time of the isotope in the rock to assess its age. The accuracy of this method is assured by the fact that when these isotopes decay, they are retained in the rock. Isotopic dating is not very accurate in sedimentary rocks because they contain particles from older rocks.
5.972 × 10^24 kg is the correct answer
A radioactive element with a half-life of 1,000 years, and starting mass of 20 grams, will need 2,000 years to decrease to 5 grams.
Explanation:
The radioactive elements all have a specific half-life. Each element's half-life is well known, and they are used by scientists of numerous fields as they are excellent for determining the age of a particular item, be it or organic or non-organic nature. In this case, we have a radioactive element with a half-life of 1,000 years, and starting mass of 20 grams.
The half-life basically means that half of the mass of an element is lost during a particular period of time. For the element in question we need to find out how much time will be needed for it to decrease to 5 grams. In order to get to the result, we just need to add 1,000 years on every decrease of half of the mass:
20/2 = 10
10/2 = 5
So in 1,000 years, the element in question will decrease to 10 grams, and in further 1,000 years (2,000 cumulatively) it will decrease to 5 grams.
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