Answer to Question 1
As long as radiation dominated the early Universe, normal baryonic matter could not contract to form galaxies and stars. Dark, non-baryonic matter does not interact with electromagnetic radiation, and was not affected by the intense radiation.
Tiny fluctuations in the texture of the big bang were caused by quantum mechanical effects. As the Universe expanded, these tiny fluctuations would have been stretched to very large, but subtle, variations in the gravitational field of the Universe. Since dark matter was not affected by radiation, it began to clump around areas of higher gravitational field.
At the time of recombination, baryonic matter was smoothly spread through the Universe, but dark matter was already clumped in filaments. After recombination, ordinary matter quickly gravitated to regions of high dark-matter density.
Dark matter clumping allowed normal matter to clump and begin producing stars and galaxies much faster than normal matter could have done on its own.
Answer to Question 2
Earth is a solid body and rotates equally at all latitudes. The Sun does not rotate as a rigid body; this is possible because the Sun is entirely gas. For example, the equatorial region of the photosphere rotates faster than do regions at higher latitudes. At the equator, the photosphere rotates once every 24.5 days, but at latitude 45 degrees, one rotation takes 27.8 days. This phenomenon is called differential rotation. Helioseismology maps of rotation in the Sun's interior reveal that the gas at different levels also rotates with different periods, another type of differential rotation. Both types of differential rotation seem to be involved in the Sun's magnetic cycle.
The first dark spot observed on Uranus. Image obtained by the HST ACS in 2006.
Medial view of tracts revealed by removing gray matter from a midsagittal section
The early stages of transcription in prokaryotes
MRI scans of normal elderly person compared to one with Alzheimer's
The stages of meiosis