There are all sorts of ways to reconstruct the history of life on Earth. Pinning down when specific events occurred is often tricky, though. For this, biologists depend mainly on dating the rocks in which fossils are found, and by looking at the “molecular clocks” in the DNA of living organisms.
There are problems with each of these methods. The fossil record is like a movie with most of the frames cut out. Because it is so incomplete, it can be difficult to establish exactly when particular evolutionary changes happened.
Modern genetics allows scientists to measure how different species are from each other at a molecular level, and thus to estimate how much time has passed since a single lineage split into different species. Confounding factors rack up for species that are very distantly related, making the earlier dates more uncertain.
These difficulties mean that the dates in the timeline should be taken as approximate. As a general rule, they become more uncertain the further back along the geological timescale we look. Dates that are very uncertain are marked with a question mark.
Answer:
it illustrated natural selection because the most favorable traits live longer than the unfavorable traits.
Explanation:
The answer is gliding. Abduction, rotation (external and internal) and extension all occur in most joints including the ball-and-socket , saddle and condyloid joints. The shoulder joint is a ball-socket joint. Gliding occurs in intercarpal joints of the hands.
Answer:
Explanation:
-Sodium-potassium pump (exchange of sodium and potassium ions across cell walls)
-Amino acids moving along the human intestinal tract.
-Calcium ions moving from cardiac muscle cells.
-Glucose moving in or out of a cell.
-A macrophage ingesting a bacterial cell.
Answer:
no
Explanation:
matter can neither be created nor destroyed so all matter is reused
