Question

early scientists believed that the origins of earth was best explained by
the gravity of the sun capturing an object floating by (the capture theory)
a piece of the early sun was flung out into space which then became our planet (the fission theory)
a giant impact event on another celestial body (the giant impact theory)
coalescence of dust and gas from a rotating nebular cloud (the nebular theory)

Explanation:

The Fission Theory was an early idea about Earth's origin. It proposed that a part of the early Sun was thrown out into space and formed Earth. The Capture Theory (capturing a floating object) is less likely as early scientists might have thought more about the Sun's direct relation. The Giant Impact Theory (impact on another body) and Nebular Theory (nebular cloud coalescence) are more modern or complex theories compared to the simple Fission - related early view.

Answer:

a piece of the early Sun was flung out into space which then became our planet (The Fission Theory)