Exist-about having an independent existence.

Exist in its core meaning is about something or someone having an independent existence,so not change with time. 

When we say objects exist,we have to always mention the time period during which it exists.

 Existence of objects related with time. 

Example

Suppose a table (a)exist today. Somebody comes and reshape it to a chair(a).  If we go to see the table (a)tomorrow,in the same location table (a) will not be there. only a chair (a) is there. 

Today 

we say table (a)exist

Chair(a) doesn't exist

Tomorrow 

We will say table(a) doesn't exist

Chair (a) exist

What we understand from this?

Existence of objects related to time. 

So existence of objects are not an independent existence 

So we can say objects are present in a particular time period. 

When we say someone or something exist they shouldn't depend on anything else for their existence.

 If they are changed by time or any other external factor, we can't say they really exist.