The oceans may indeed have come from outer space.
Researchers have managed to find ice which contains the exact same water composition as that found in the oceans of the earth on the Hartley 2 comet. For years the notion that the oceans of our planet, which formed 8 million years after Earth was formed, came about due to comets that carried ice.
While ice is often found in many comets, what makes Hartley 2 so unique is the D/H ratio (of (1.558 ± 0.001) × 10−4) which proportionate to deuterium in water. Deuterium is a hydrogen atom with an extra neutron in its nucleus. And the ice in comet Hartley 2 contained this exact ratio of deuterium as that found in water on Earth. The comet Hartley 2 comes from the Kuiper belt which is little further away from Pluto.
Hartley 2, captured by NASA's EPOXI mission.
“We were all surprised,” said University of Michigan astronomy professor Ted Bergin to The Register, who helped make the discovery. “Life would not exist on Earth without liquid water, and so the question of how and when the oceans got here is a fundamental one,” said Professor Bergin. “It’s a big puzzle, and these new findings are an important piece.”