Why is the variety of life on Earth now different than it was in Earth’s past?

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.

early greek culture has had an important impact on government and education. first of all, they established the democratic political systems and procedures we have today. consequently, we inherited trial by jury for example. considering education, greek philosphers, mathematicians set he intellectual basis of different areas of studies. in addition, the alphabet originated from the phoenician alphabet into the one we have today and the first library was built in egypt. moreover, greek culture has an impact in current art, architecture and sports disciplines.