tailieunhanh - EARTH AS AN EVOLVING PLANETARY SYSTEM Part 9

Quá trình hình thành Trái Đất được hoàn thiện trong vòng 10 đến 20 triệu năm.[19] Lúc đầu ở dạng nóng chảy, lớp vỏ ngoài của Trái Đất nguội lại thành chất rắn trong khi nước bắt đầu tích tụ trong khí quyển. | 362 Comparative Planetary Evolution Figure Comparison of channel cross-sections for cataclysmic flood channels on Mars upper two with straits Gibraltar and Bosporus and river channels on the Earth. Modified from Baker 2001 . N. Kasei Ayres Gibraltar m 500 5 10 km Bosporus Altai Missoula . w. . Amazon Mississippi before the terminal large impact event about Ga. Continued fracturing and volcanism on Mars extended to at least 1000 Ma and perhaps 100 Ma. Venus Comparison with the Earth. Unlike the other terrestrial planets Venus is similar to the Earth both in size and mean density and g cm3 respectively Table . After correcting for pressure differences the uncompressed density of Venus is within 1 of that of the Earth indicating that both planets are similar in composition with Venus having a somewhat smaller core mantle ratio. Although both planets have similar amounts of N2 and CO2 most of the Earth s CO2 is not in the atmosphere but in carbonates. Venus also differs from the Earth by the near absence of water and the high density and temperature of its atmosphere. As described later Venus may at one time have lost massive amounts of water by the loss of hydrogen from the upper atmosphere. Unlike the Earth Venus lacks a satellite has a slow retrograde rotation 244 Earth days for one rotation and does not have a measurable magnetic field. Because Venus orbits the Sun in only 225 days the day on Venus 244 Earth days is longer than the year. The absence of a magnetic field in Venus may be caused by the absence of a solid inner core because as described in Chapter 5 crystallization of an inner core may be required for a dynamo to operate in the outer core of a planet. Of the total Venusian surface 84 is flat rolling plains some of which are more than 1 km above the average plain elevation. Only 8 of Members of the Solar System 363 the surface is true highlands the remainder 16 lies below the average radius forming broad shallow basins. This is .