PBS Space Time Season 2020 Episode 13 How We Know the Earth is Ancient

How We Know the Earth is Ancient is the thirteenth episode of season 2020 of the PBS Space Time series. In this episode, the hosts delve into the scientific methods used to determine the age of the Earth.

The episode starts with a brief history of how scientists have tried to determine the age of the Earth over the years, from Archbishop Ussher's biblical calculations in the 17th century to the discovery of radioactivity in the 20th century. The hosts then explain how radioactive isotopes, such as uranium and potassium, decay over time at a known rate, allowing scientists to calculate the age of rocks and minerals using the ratio of the radioactive isotope to its stable counterpart.

The hosts explore the different methods used to measure the age of rocks and minerals, including radiometric dating, argon-argon dating, and lead-lead dating, each with its own advantages and limitations. They also discuss the techniques used to date the oldest rocks on Earth and the oldest meteorites, which give insight into the early history of the solar system.

The episode then moves on to the concept of geologic time scales, which divide Earth's 4.5 billion year history into different eras, periods, and epochs based on major events such as mass extinctions, volcanic eruptions, and the formation of continents and oceans. The hosts explain how these time scales were created using a combination of radiometric dating and the study of rock layers and fossils.

Throughout the episode, the hosts emphasize the importance of multiple lines of evidence in corroborating the age of the Earth, including the ages of the oldest rocks and meteorites, the ages of the moon and other planets, and the ages of the earliest life forms on Earth. They also discuss some of the challenges and controversies in dating the Earth, such as the difficulty in accurately dating rocks that have been metamorphosed or weathered over time, and the ongoing debate over the exact age of the Great Oxygenation Event, which transformed Earth's atmosphere over 2 billion years ago.

The episode concludes with a discussion of the implications of knowing the Earth's age. The hosts point out that the vastness of geologic time can be difficult for the human mind to comprehend, but that it gives us an appreciation for the slow but profound changes that have shaped our planet over billions of years. They also note that our knowledge of the Earth's age and history allows us to make more accurate predictions about the future, such as the effects of climate change on the planet.

In summary, How We Know the Earth is Ancient is an informative and engaging episode that explores the scientific methods and evidence used to determine the age of the Earth and the importance of geological time scales in understanding Earth's history. The hosts strike a good balance between technical detail and layman-friendly explanations, making the episode accessible to a wide audience. Anyone interested in earth sciences or the history of our planet will find this episode engaging and informative.