  We integrated the orbital evolution of 30,000 Jupiter-family comets, 1300
resonant asteroids, and 7000 asteroidal, trans-Neptunian, and cometary dust
particles. For initial orbital elements of bodies close to those of Comets 2P,
10P, 44P, and 113P, a few objects got Earth-crossing orbits with semi-major
axes $a$$<$2 AU and moved in such orbits for more than 1 Myr (up to tens or
even hundreds of Myrs). Four objects (from 2P and 10P runs) even got
inner-Earth orbits (with aphelion distance $Q$$<$0.983 AU) and Aten orbits for
Myrs. Our results show that the trans-Neptunian belt can provide a significant
portion of near-Earth objects, or the number of trans-Neptunian objects
migrating inside the solar system can be smaller than it was earlier
considered, or most of 1-km former trans-Neptunian objects that had got
near-Earth object orbits for millions of years disintegrated into mini-comets
and dust during a smaller part of their dynamical lifetimes. The probability of
a collision of an asteroidal or cometary particle during its lifetime with the
Earth was maximum at diameter $d$$\sim$100 $\mu$m. At $d$$<$10 $\mu$m such
probability for trans-Neptunian particles was less than that for asteroidal
particles by less than an order of magnitude, so the fraction of
trans-Neptunian particles with such diameter near Earth can be considerable.
