Our home, Planet Earth, is a very wet place. In contrast, our neighbor, Mars, is a desert. Three-quarters of Earth's surface is covered by water. It's mainly in liquid form, though ice exists over the northern and southern polar oceans and water vapor is present in the atmosphere. Being 93 million miles from the sun, conditions are such that water "sticks" to our planet. All three phases can coexist, so water remains a prominent feature. Dating of meteorites indicate that our solar system is about 4.6 billions years old. The older sedimentary rocks, formed through processes requiring water, are about 3.9 million years old. Water must have been present at least that long ago then. It is not clear where this water came from, but the traditional view has been that it was a byproduct of planetary cooling, our seas resulting from the condensation of water vapor originating in the rocks of the Earth's crust. In the last decade, some new and radically different ideas have emerged from the scientific community, particularly from University of Iowa astrophysicist Louis A. Frank. Frank took note of mysterious dark spots in high-resolution photographs taken in the high-elevation mesosphere of the polar regions. He hypothesized that they might be house-sized, 40- to 60-ton ice balls from small comets that were entering the atmosphere at the astonishing rate of 40,000 a day.
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wouldnt want to get in the way of one of those!!!