1. **State the problem:** We are given two numbers in scientific notation: Earth is about $4.5$ billion years old and primate fossils date back about $45$ million years. 2. **Write each number in standard notation:** - $4.5$ billion years means $4.5 \times 10^9$ years. - $45$ million years means $45 \times 10^6$ years. Convert to standard notation: - Earth age: $$4.5 \times 10^9 = 4,500,000,000$$ - Primate fossils age: $$45 \times 10^6 = 45,000,000$$ 3. **Find how many times as old Earth is compared to primate fossils:** Divide Earth's age by primate fossils' age: $$\frac{4,500,000,000}{45,000,000} = \frac{4.5 \times 10^9}{4.5 \times 10^7} = 10^{9-7} = 10^2 = 100$$ 4. **Explain the thinking:** Earth is about 100 times as old as the primate fossils because when dividing the two numbers, the powers of ten subtract, leaving $10^2$, which equals 100. **Final answers:** - Earth age in standard notation: $4,500,000,000$ - Primate fossils age in standard notation: $45,000,000$ - Earth is about 100 times as old as the primate fossils.