The material that makes up the planets has been affected, to a greater or lesser degree, by events occurring after the planets’ formation. Particularly on Earth, where erosion, geology, and chemistry have left little pristine primordial material, the story of the last 4.6 billion years is a complex (but fascinating) one. However, some of the samples we have obtained from space provide a record of the material that first came together to form our Solar System. Radiometric dating techniques similar to those used in paleontology can help reveal the history of these samples. The story they tell is consistent with what we know from observing distant objects with our telescopes: gas and dust form stars and planets over billions of years of cosmic time.
All the material that makes up our Earth, including the water in our oceans, the nitrogen in our air, and the iron in our rocks and in our bodies, ultimately came from space, and provided the stage and the substance from which life on Earth got its start. Later impacts from space have also led to profound changes in the evolution of life on Earth, at times resulting in the extinction of almost all life on our planet. Though all known life is firmly rooted on Earth, its history is clearly interwoven with that of the Universe as a whole.