Time is essentially one event following another. It is one of those things that is self-existent. The difference between us here in the world is that we measure time according to the rotation of the earth, and the earth around the sun, hence we have years, months, weeks, days, hours, minutes and seconds. The reason we measure time is that our life spans are limited. In eternity, it seems timeless, because time is not measured there. It is called "eternity" because there is no beginning nor end to the series of events. If we lived forever in eternity, we wouldn't have to worry about measuring time because we wouldn't be conscious of having a limited amount of time available to us. We would have plenty of time to do everything we want to do, whereas in our present existence, we are under pressure to do everything we want, and have to make choices about whether we can achieve something or not before our time has run out.
Also, time on earth is relative. The lifespan of a butterfly is usually measured in days, so the activities it does is severely limited to just being able to mate and perpetuate the species, while the lifespan of a tortoise is measured in hundreds of years, so it appears not to be in a hurry to do anything.
Therefore, our consciousness of time exists only because we measure it, in terms of recording past history and deciding how much time we have left to accomplish what we want to do in life before we get too old and die.
