UCLA: Moon Was Produced by Head-on Collision
Posted: Fri Jan 29, 2016 6:11 pm
Moon Was Produced by a Head-on Collision between Earth and a Forming Planet
University of California, Los Angeles | 2016 Jan 28
Oxygen isotopic evidence for vigorous mixing during the Moon-forming giant impact - Edward D. Young et al
University of California, Los Angeles | 2016 Jan 28
UCLA-led research reconstructs massive crash, which took place 4.5 billion years ago
[img3="The extremely similar chemical composition of rocks on the Earth and moon helped scientists determine that a head-on collision, not a glancing blow, took place between Earth and Theia. (Copyright: William K. Hartmann)"]http://cms.ipressroom.com.s3.amazonaws. ... 37-prv.jpg[/img3][hr][/hr]The Moon was formed by a violent, head-on collision between the early Earth and a “planetary embryo” called Theia approximately 100 million years after the Earth formed, UCLA geochemists and colleagues report.
Scientists had already known about this high-speed crash, which occurred almost 4.5 billion years ago, but many thought the Earth collided with Theia (pronounced THAY-eh) at an angle of 45 degrees or more -- a powerful side-swipe (simulated in a 2012 YouTube video). New evidence reported Jan. 29 in the journal Science substantially strengthens the case for a head-on assault.
The researchers analyzed seven rocks brought to the Earth from the Moon by the Apollo 12, 15 and 17 missions, as well as six volcanic rocks from the Earth’s mantle -- five from Hawaii and one from Arizona.
The key to reconstructing the giant impact was a chemical signature revealed in the rocks’ oxygen atoms. (Oxygen makes up 90 percent of rocks’ volume and 50 percent of their weight.) More than 99.9 percent of Earth’s oxygen is O-16, so called because each atom contains eight protons and eight neutrons. But there also are small quantities of heavier oxygen isotopes: O-17, which have one extra neutron, and O-18, which have two extra neutrons. Earth, Mars and other planetary bodies in our solar system each has a unique ratio of O-17 to O-16 -- each one a distinctive “fingerprint.” ...
Oxygen isotopic evidence for vigorous mixing during the Moon-forming giant impact - Edward D. Young et al
- Science 351(6272):493 (29 Jan 2016) DOI: 10.1126/science.aad0525