Answer: It was obtained 8515 years ago
Explanation:
Expression for rate law for first order kinetics is given by:

where,
k = rate constant
t = age of sample
a = let initial amount of the reactant
a - x = amount left after decay process
a) to find the rate constant:
Half life is the amount of time taken by a radioactive material to decay to half of its original value.


b) for completion of 36% of reaction


t = 8515 years
The time was 8515 years.
The answer to this question is Fossil Fuels
Answer/Explanation:
Density-dependent limiting factors are non living and biotic factors that affect the size and growth of a population based on the population density, while density-independent limiting factors are those factors that do not depend on the density of a population before they can have an effect on the growth and size of the population.
Examples of density-dependent limiting factors are predation, disease, Parasitism, competition. These rely on the density of a population in order to affect the growth and size of a population.
On the other hand, examples of density-independent limiting factors are pollution, flood, temperature.
The correct answer is A! Hope this helped!