Read Online The Universe Within by Neil Shubin - Free Book Online Page A
Authors: Neil Shubin
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liquid water may have formed a few different times, only to evaporate away. As a break from this desolation, you might hope for beautiful moonlit nights. Forget about it. There was no moon.
Artifacts of the transformation of this primordial world into our modern one are strewn across different bodies of thesolar system. Six missions landed on themoon and returned samples to Earth. Carrying mini geological kits, astronauts collected rocks from craters, highlands, and lowlands of the lunar surface. The specimens are today stored in liquidnitrogen in repositories in Houston and San Antonio. A number of small moon fragments have been given as gifts to foreign dignitaries, while others grace public exhibits. The bulk of the rocks, about 850 pounds in all, remain to be studied. The few samples that have made it to labs tell important stories of the origin of our world.
One of the biggest lessons frommoon rocks is how normal many of them are. In terms of mineral content and structure, moon rocks are more similar to those on Earth than others in the solar system. One similarity is particularly telling.Oxygen atoms can exist in different forms, defined by the number ofneutrons in the nucleus. By measuring the neutron-heavy and neutron-lightversions ofoxygen in any rock, a very informative ratio can be calculated. Each body in the solar system carries a unique chemical signature written in the proportion of different versions of oxygen in their rocks. The reason is that the oxygen content inside a planet’s rocks is sensitive to itsdistance from thesun when it formed. The oxygen composition of moon rocks, though, is virtually identical to those of Earth. This means that the moon and Earth formed at the same distance from the sun—perhaps in the same orbit.
With all of these similarities, there remains one very significant difference between moon rocks and those of Earth. Moon rocks almost entirely lack one class of elements, the so-calledvolatiles. These elements—nitrogen,sulfur, andhydrogen—share one important geological fact: they tend to vaporize when things get hot (hence the name volatiles). Some great event in the distant past must have baked the moon rocks, releasing their volatiles.
The lessons of the moon rocks are clear—the minerals on the moon formed at the same orbital distance from the sun as Earth and then suffered some kind of blast. What do these facts tell us of the origin of the moon?
The current theory for the formation of the moon envisions something like a cosmicdemolition derby. In these automotive mosh pits, common at fairgrounds in the 1970s, cars intentionally smashed into one another, with the last car running being the winner. Along the way, cars would slam into each other with wild abandon. The most violent of these collisions would eject the light outer layers of the cars, hubcaps and bumpers, leaving the inner ones hopelessly entangled.
This type of collision offers an insight into how theEarth-moon system came about. Over 4.5 billion years ago, a large, perhapsMars-sized,asteroid is thought to have collided with the forming Earth. Much like the twisted mélange of car parts in a demolition derby crash, the collision ejected lighter parts of each body while the heavier pieces fused. The lighter debris, consisting of dust and smaller particles, now depleted ofvolatile elements, began to orbit Earth as a disk. Over time, this debris disk coalesced as the moon. The cores of the two bodies did not propel into space but liquefied under the great heat of the impact, only later to cool and solidify as the new core of Earth. In addition, the impact so whacked Earth that it left a 23.5-degree tilt in its axis ofrotation.
Initially, there were two large bodies in the same orbit of the sun. Then they collided, forming what we know as Earth and moon today. Ever since that impact, the two bodies have been locked in an orbital dance—Earth and moon exert gravitational pull on each other, while the laws of
Artifacts of the transformation of this primordial world into our modern one are strewn across different bodies of thesolar system. Six missions landed on themoon and returned samples to Earth. Carrying mini geological kits, astronauts collected rocks from craters, highlands, and lowlands of the lunar surface. The specimens are today stored in liquidnitrogen in repositories in Houston and San Antonio. A number of small moon fragments have been given as gifts to foreign dignitaries, while others grace public exhibits. The bulk of the rocks, about 850 pounds in all, remain to be studied. The few samples that have made it to labs tell important stories of the origin of our world.
One of the biggest lessons frommoon rocks is how normal many of them are. In terms of mineral content and structure, moon rocks are more similar to those on Earth than others in the solar system. One similarity is particularly telling.Oxygen atoms can exist in different forms, defined by the number ofneutrons in the nucleus. By measuring the neutron-heavy and neutron-lightversions ofoxygen in any rock, a very informative ratio can be calculated. Each body in the solar system carries a unique chemical signature written in the proportion of different versions of oxygen in their rocks. The reason is that the oxygen content inside a planet’s rocks is sensitive to itsdistance from thesun when it formed. The oxygen composition of moon rocks, though, is virtually identical to those of Earth. This means that the moon and Earth formed at the same distance from the sun—perhaps in the same orbit.
With all of these similarities, there remains one very significant difference between moon rocks and those of Earth. Moon rocks almost entirely lack one class of elements, the so-calledvolatiles. These elements—nitrogen,sulfur, andhydrogen—share one important geological fact: they tend to vaporize when things get hot (hence the name volatiles). Some great event in the distant past must have baked the moon rocks, releasing their volatiles.
The lessons of the moon rocks are clear—the minerals on the moon formed at the same orbital distance from the sun as Earth and then suffered some kind of blast. What do these facts tell us of the origin of the moon?
The current theory for the formation of the moon envisions something like a cosmicdemolition derby. In these automotive mosh pits, common at fairgrounds in the 1970s, cars intentionally smashed into one another, with the last car running being the winner. Along the way, cars would slam into each other with wild abandon. The most violent of these collisions would eject the light outer layers of the cars, hubcaps and bumpers, leaving the inner ones hopelessly entangled.
This type of collision offers an insight into how theEarth-moon system came about. Over 4.5 billion years ago, a large, perhapsMars-sized,asteroid is thought to have collided with the forming Earth. Much like the twisted mélange of car parts in a demolition derby crash, the collision ejected lighter parts of each body while the heavier pieces fused. The lighter debris, consisting of dust and smaller particles, now depleted ofvolatile elements, began to orbit Earth as a disk. Over time, this debris disk coalesced as the moon. The cores of the two bodies did not propel into space but liquefied under the great heat of the impact, only later to cool and solidify as the new core of Earth. In addition, the impact so whacked Earth that it left a 23.5-degree tilt in its axis ofrotation.
Initially, there were two large bodies in the same orbit of the sun. Then they collided, forming what we know as Earth and moon today. Ever since that impact, the two bodies have been locked in an orbital dance—Earth and moon exert gravitational pull on each other, while the laws of
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