An element cannot be broken down any further. Elements can be found on the periodic table
17 protons 17 electrons 18 neutrons
Answer: isotopes
Explanation: I remember this from when I took honors chemistry, they are know as isotopes.
The first answer would be:
Measure the sequence of events on earth over time.
I believe the second answer would be:
The age of earth. ( I say this because geological time is used to describe timing and the relationship of events in earths history)
I’m not sure about number 3 but I hope this was somewhat useful!!