For decades, planetary scientists debated the primary origin of Earth’s surface water, generally favoring the 'late veneer' hypothesis, which posits that water-rich asteroids bombarded the planet post-formation. Recently, however, geochemical analyses of deep-mantle rocks have challenged this consensus by revealing isotopic signatures identical to those of ancient nebular dust. These findings suggest that water was actually present during Earth's initial accretion, locked within the planetary interior and later released through volcanic degassing. While some researchers argue that both mechanisms contributed significantly, the discovery of early mantle water has fundamentally shifted focus toward internal geological processes rather than external cosmic impacts.
Which choice best describes the overall structure of the text?
- AIt presents a consensus scientific theory, details a study that supports that theory, addresses a minor limitation of the study, and proposes a compromise between competing views.
- BIt details the specific geochemical methods used to analyze deep-mantle rocks, explains how those rocks were formed, and argues that volcanic degassing is the sole cause of planetary accretion.
- It outlines a long-standing scientific hypothesis, introduces new evidence that challenges it, explains an alternative explanation supported by that evidence, and notes a shift in the research community's focus.Cevap
- DIt claims that asteroid bombardment was the sole source of Earth's water, explains how volcanic degassing prevents water from escaping the mantle, and predicts when the next cosmic impact will occur.