Could comets have been the source for water and life on Earth?
Life on Earth and on the Moon
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Since comets contain huge amounts of ice and rock, astronomers have long speculated that comets colliding with Earth may have deposited substantial amounts of water onto Earth’s surface early in our planet’s history. Recently, additional hypotheses have been proposed positing that biological ingredients for life—such as complex protein and DNA molecules—may have been formed elsewhere in the solar system or the galaxy; they may have been frozen into cometary ice and then carried down to Earth’s surface billions of years ago, seeding our planet with the biological precursors for life. The latest research suggests, however, that while some water may well have been brought to Earth by extraterrestrial objects, complex organic molecules probably break down too quickly when exposed to the extreme cold and radiation environment of interplanetary space to survive a multi-million-year ride embedded in cometary ice.