Final answer:
Statement 3 acknowledges the flawed early estimates but is incorrect in suggesting that the Earth is thought to be much younger than it actually is. The Earth is approximately 4.54 billion years old, which we know due to radiometric dating and geochronology.
Step-by-step explanation:
The truth about the early, incorrect dates for the age of the Earth lies in the work of scientists such as Charles Darwin and Lord Kelvin, who made initial estimates based on the knowledge available at their time.
Darwin's contributions were primarily in the field of biology, and he did not himself estimate the age of the Earth. Instead, geologists of Darwin's time, who influenced his thinking, like Charles Lyell, pointed towards the Earth being much older than 6,000 years; however, no precise age was given by Darwin.
On the other hand, Kelvin estimated the age of the Earth using cooling rates, but he proposed a much smaller age of 20 to 40 million years, not 20 billion years.
The current scientific consensus, supported by radiometric dating, suggests that the Earth is approximately 4.5 billion years old. Kelvin and Darwin's discussions on the subject, however, did help spark the necessary debates and research that eventually led us to a more accurate estimate.
Therefore, of the options given, statement 3 is true as it acknowledges the flawed early estimates but incorrectly claims the Earth is thought to be much younger than the true age.
The age of the Earth is now known to be about 4.54 billion years, with evidence from stratigraphy, paleontology, and geochronology.