The controversy over where Earth's water may have come from is an ongoing debate within the Geosciences community. For years, scientists have grappled with the issue. Some scientists believe that water-ice from comets impacted the Earth early it's history may have provided enough water for the planet. Other scientists, however, are skeptical of this claim. Another theory proposes that volcanic eruptions released water vapor gas into the atmosphere of the young Earth and that the vast oceans and waterways formed this way. Recent data coming out appears to be showing the "comet water-ice" theory to be less and less likely, however.
Sources:
Rosetta Spacecraft's Comet Water Discovery: What It Means For Earth
Earth Story - Time Travelers (Minutes 41:25-41:47)
Rosetta:
URL: The URL for this source ends in html. This indicates that the story appeared on a webpage. While the webpage might have factually information being presented, I should certainly be more skeptical of what is being said within it.
Author: The webpage was written by Miriam Kramer. Kramer has degrees in both journalism and anthropology (Miriam Kramer).
Last Updated: December 12th, 2014. Most of the links are related to the Rosetta Spacecraft in some way. Also, the links are still working.
Purpose: The purpose of the text is to inform the reader about new data from the Rosetta Space Probe. The story, using data collected from the Probe, appears to be stating that comets may not have delivered water to the early Earth after all.
Graphics: There are many images within the story. The images include a picture of the comet being researched, a picture of the Rosetta Space Probe, and a graphic representation of the data collected.
Position on Subject: The story takes the position that comets probably did not deliver water to the early Earth. This statement appears to be backed by the data from the Rosetta Project, however. The data from the mission indicates that the water vapor on the comet contains much higher levels of deuterium hydrogen atoms (Isotope of hydrogen; has one proton, one electron and one neutron rather than the normal one proton and one electron normally found in hydrogen) than normal hydrogen atoms. Scientists supporting theories that water on Earth arrived through some different method stand to be proven correct if the data holds that all comets being researched have water that has a different chemical makeup than what we see on Earth.
Links: There is a section titled 'Editor's Recommendations" near the bottom of the page. However, the sources linked include a comet quiz and pictures of comets. Therefore, they might not be the most credible of sources to follow.
Earth Story:
URL: The video was found on YouTube, so the URL is a bit different from other sources. not .org, .html, or .net exists in the URL. So, the credibility of the source could be in question already.
Author: The video is from a television series called "Earth Story". The show is a documentary series that appeared on BBC and is narrated by Aubrey Manning; an English zoologist (Earth Story). It was directed by Danielle Peck and Simon Singh.
Last Updated: The series came out in 1998 and was only intended to be run for one season. As a result of the age, no real links to websites are listed in the film. As well, the age calls into question the reliability of the information.
Purpose: The purpose of this film series was to educate viewers about the geologic processes that have shaped Earth. The episode in question served to inform viewers about the age of the Earth and also introduce theories on how life may have started on Earth, as well as where Earth's water may have come from.
Graphics: Being a documentary film, the entire source is a moving graphic image! However, the series, being focused on geology, typically involves shots of sweeping vistas or volcanic islands. These sites were chosen to show how processes such as erosion and volcanic activity have shaped Earth.
Position on Subject: The short snippet of the video I was focused on talked about how water vapor was released into the atmosphere by volcanoes, not comets or asteroids. This indicates to me that the film series takes the position that volcanic activity released water vapor into the atmosphere. This water vapor eventually condensed and fell back to the Earth as precipitation (rain, snow, etc). If later research proves that volcanoes are mostly responsible for waters appearance on Earth, then those scientists supporting that theory stand to be proven correct in their hypotheses. However, one question that scientists sticking to the comet water ice theory might ask is how did the water vapor come to be within the volcanoes to begin with?
Links: While there are no links to other websites in the video, the credits of the film list people and foundations that contributed to making the film. Since the episode in question is from a BBC documentary, one can assume that it is a rather reliable source of information, despite the age.
gnuckx. Etna Volcano Paroxysmal Eruption. January 13th, 2011 via Flickr. Attribution License.
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