Origin of the oceans and the atmosphere of the Earth
- Univ. of Toledo, OH (United States)
In the terrestrial zone of the Solar Nebula, the temperature of the dusty particles that sedimented from the gas phase to form the Earth cannot be directly established. However, it can be deduced from the known accretion temperature of chondrites, combined with any reasonable temperature gradient from 2.6 to 1 A.U. The authors find that it had to be close to 1,000 K, implying complete degassing of the grains. In particular, all carbon was in gaseous CO and all H[sub 2]O was steam (no silicates were hydrated). The subsequent agglomeration of planetesimals into the Earth was therefore completely devoid of volatiles. A more recent process must exist to bring carbon, nitrogen and water to the Earth. A [open quotes]primary[close quotes] atmosphere has not been captured later (by gravitation) from the nebular gas, as established by the present abundances of the rare gas isotopes. There remains therefore a single possible source for our oceans and our atmosphere: during the following 500 million years, the formation of the giant (comets). A testimony of this bombardment is still visible in the numerous craters of the Moon. A model for the orbital diffusion of those icy planetesimals that Chiba's (1991) estimates deduced from the lunar craters. Our model produces ten times too much water for our present oceans, and one thousand times too much atmosphere. This is consistent with the very large losses implied by the numerous impacts of larger and larger bodies in the final stages of accretion. At the end, a large amount of very fine dust reached the ground by floating gently through the upper atmosphere; it came from the tails of those numberless comets that visited our inner solar system. This dust was able to seed the primitive oceans with organic compounds without destroying them. Hence life was able to start early, as soon as accretion ended.
- OSTI ID:
- 5779262
- Journal Information:
- American Astronomical Society, Bulletin; (United States), Vol. 24:3; ISSN 0002-7537
- Country of Publication:
- United States
- Language:
- English
Similar Records
Impact of Radiogenic Heating on the Formation Conditions of Comet 67P/Churyumov–Gerasimenko
THE IRREGULAR SATELLITES: THE MOST COLLISIONALLY EVOLVED POPULATIONS IN THE SOLAR SYSTEM