| · Catastrophic | · Nebular |
| Geo. Louis Le Clerc (1749) (Comte de Buffon)  (Collison of sun and comet) | Kant (1754), Laplace (1796)  (Nebular hypothesis) |
| Chamberlain & Moulton (1900)  (Near approach of star) | Cosmic Evolution of Earth |
Hoyle (1940's) (Explosion of companion star) | von Weiszacker (1940's) (Neo-nebular hypothesis) |
Figure 2.1 Hypotheses for earth's origin (from The Changing Earth - Introduction to Geology (2nd ed.), by Mears, Jr., D. Van Nostrand Co., 1977).
Figure 2.2
Figure 2.3 A diagrammatic summary of the Solar System. The Sun and the planets are drawn
to scale in the lower half. All the planetary orbits except those of Pluto and
of Mercury lie in nearly the same plane as the Earth's orbit, The asteroid belt
and a highly eccentric comet orbit are shown
(from Understanding the Earth (2nd ed.), by Gass, Smith, & Wilson,
The M.I.T. Press, 1972).
Figure 2.4 Three possible origins of the Moon
(from The Changing Earth - Introduction to Geology (2nd ed.),
by Mears, Jr., D. Van Nostrand Co., 1977).
Figure 2.5 Numerical simulation by Benz et al. (1986) for impact of Earth by a
body of (one Earth mass )/7 (i.e., Mars size). The initial conditions are 0 km/sec relative
velocity at infinity but the present Earth-Moon system angular momentum.
The iron cores are circled. Time is given in hours from impact.
The clump in the lower right corner of the last frame has exactly one Moon
mass (35 particles). There is another 1/2 - 1/3 Moon mass in a disk around
Earth. No iron is in orbit. Subsequent evolution after the final frame
is not known. Results courtesy of W. Benz (Los Alamos National Laboratory).