Explain how fossils and paleontology give evidence for evolution by natural selection. How is the age of a fossil determined? How do scientists infer relationships among fossils? Please consider and use the following words in your explanation: fossil, gap species or missing link, evolution, extinction and Tiktaalik

Fossils are the preserved remains or traces of ancient organisms that have been embedded in rock layers over millions of years. Paleontology is the scientific study of these fossils, through which scientists can reconstruct past life on Earth. By analyzing fossils, paleontologists gain insights into the process of evolution by natural selection.

The evidence for evolution by natural selection through fossil records includes:

- Transitional forms or "missing links": Fossils can show gradual changes over time from one species to another, portraying how modern organisms evolved from extinct ones. The discovery of "missing links" or gap species, like Tiktaalik, for example, bridges the gap between aquatic fish and terrestrial tetrapods. Tiktaalik had structures that are intermediate in form between the fin bones of fish and the limb bones of tetrapods, showing how the limbs of tetrapods could have evolved from fins.

- Records of Extinction: The fossil record displays numerous species that are no longer present on Earth today. By studying their features and the environmental shifts at the time, scientists can deduce the reasons behind extinctions, which demonstrate the concept of "survival of the fittest," central to natural selection.

To determine the age of a fossil, scientists often use a method called radiometric dating, particularly when the fossils are older than about 50,000 years. This technique involves measuring the decay of radioactive isotopes within the rocks surrounding the fossils. Isotopes like Carbon-14 can be used for more recent fossils, while longer-lived isotopes such as Uranium-238 are used for dating older geological formations.

Scientists infer relationships among fossils by analyzing their physical characteristics and using computer algorithms to construct phylogenetic trees, which show the inferred evolutionary relationships. The placement of fossils within these trees helps to understand how traits evolved and how different species are related to each other.