What percentage of the earths solar radiation reaches earths surface

What is thought to have caused the mass extinction at the end of the cretaceous period?

The organelle pictured is found in cells of and is theorized to have once been an independent organism.

The current thought on the structure of the cell membrane is: a. a static phosphate sandwich of lipids b. a fluid-mosaic of phospholipids and proteins c. a bilayer of proteins with static lipid molecules d. an impermeable bilayer of protein molecules e. a static and permeable phospholipid single layer