There is another theory of how the precursors of life were brought to Earth—known as panspermia. Scientists theorize that comets and asteroids bombarded the early Earth, bringing complex organic materials, many of which survived the fall to our planet.

Scientists know there are such organic materials in space. In the late 1960s, radio astronomers discovered organic molecules in dark nebulae. Since that time, other sources have been found, including organic molecules existing in space bodies such as asteroids, comets, and meteorites. In 1969, analysis of a meteorite showed at least 74 amino acids within the chunk of rock. Scientists began to speculate that the organic molecules could have traveled to Earth via meteorites, cometary dust, or, during the early years of Earth, by way of comets and asteroids.

Although many scientists argue that the heat from the impact of a giant asteroid or comet would destroy any organic passengers, many other scientists disagree. They propose that only the outer layers of a large body would be affected, or that the fine, unheated dust of comets could have brought the necessary amino acids to Earth. If this theory is true, we are apparently all—from dinosaurs to humans—made of “star stuff.”