Geologists now agree that Crystals in rocks that were found in Australia prove that the earth was not a desolate inhabitable place 4.5 billion years ago during the Hadean period. These crystals found embedded in rocks know as zircons are billions of years old and they offer signs that the Earth’s plate had begun shifting during the Hadean period. The minerals show that the plates were already forming continents and oceans 4.5 billion years ago. Zircons are composed of the elements Zirconium, oxygen, and silicon. They are really hard and durable and can survive harsh conditions that erode, melt, and destroy the rocks around them. The relative amounts of oxygen isotopes show that there was water. Zircons have high levels of oxygen-18 which in minerals in clays and carbonates that form in water prefer as well. The most common oxygen isotope is oxygen-16. Scientists believe the Earth at this time was a pretty placid place with both land and oceans. The temperatures on earth were cold enough to create large areas of lands covered by ice. The sun was much younger then and emitted 30 percent less energy then it does today.
http://www.nytimes.com/2008/12/02/science/02eart.html?ref=science
7 comments:
3intersting
straighte to the point
written well
2talk more about Hadean period
be clearer on crystals in rocka
1 never knew that sun used to be less powerful than it is today
3 Good:
-general topic that was supported with evidence
-interesting
-about isotopes and elements, which are part of chemistry
2 Improvements:
-explain how scientists can tell that the minerals were forming continents
-explain the earth 4.5 billion years ago
1 Thing Learned:
-life could have formed on the earth 4.5 billion years ago, but the first life didn't appear until much later
3 Aspects well presented:
* very interesting topic
* a lot informations
* the topic was easy to understand
2 Suggestions:
*you could say if a human could live in Earth with 30% less sun energy, saying how cold it was
*you could explain more the relationship between water and zircons
Thing learned:
*That with zircons you can discover if there were water billions of years ago
1. It had good facts
2. Straight to the point
3. Easy to understand
1. You could of had more facts
2. You could have talked more about Zircons
1. I learned that Zircons could give us an idea about how the Earth was 4.5 billion years ago
1 very detailed
2 interesting topic
3 make us think about how different life could have been
1 explain what it was like 4.5 billion years ago
2 explain the zircons more
1 i didnt know what zircons were
-general topic
-interesting
-about chemistry related thing
-explain relationship between water and zircons
-explain how scientists knew minerals were forming continents
-Because zircons existed billions of years ago, so did water
3. well written
good topic with a lot of evidence
straight to the point
2. you could have added more facts
you could have explained the earth and how it was long ago
1.I learned that Zirons can show us what the earth was like 4.5 billion years ago
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