Early systems of classification grouped organisms into two main categories, plants and animals, based on visible characteristics. today, organisms are classified by domains (or superkingdoms) and by kingdoms (and subgroups of phyla, classes, orders, families, genuses, and species). how many domains and kingdoms are in the modern system of taxonomy?

(drag each tile to the correct location.) categorize each term as something that is typical of a scientific theory, a scientific hypothesis, or both. - a tentative statement used to guide scientific investigations. - makes predictions about future events. - can be tested by many independent researchers. - based on observations of natural phenomena. - a well-established, highly reliable explanation.

What was the land like over 500 million years ago? what was under the sea?

What is any method of measuring the age of an object or event in years, such as using atomic half-life?