On the geologic time scale are marked by major, striking, and worldwide changes in the type of fossils present.

An era on the geologic time scale are marked by major, striking, and worldwide changes in the type of fossils present.  

Explanation:

An era is defined as the one of the largest unit of time which is used to define a period in the history. Humans are known to be one of the oldest primates living on the earth till now. Our Earth is approximately more than 4 billion years old.

The oldest era of the Earth is named as Eoarchéen whereas the most modern era of the Earth is known as Cenozoic. The back dating is done by the method of carbon dating. In carbon dating process there is use of carbon 14 atom.  

you didn't give any options but heres what i can tell you: an inference is likely to change based on additional observations. the latter is something that you have seen or sensed using your sensory organs while the former is like a conclusion out from what you have observed.

several tissues working together form an organ, and several organs together make up an organisms.

the group of cell that carries out special jobs are tissue.