That's an incomplete description of what we are. We are not just that. We are much more.
Our senses give us a view of reality at the scale of everyday experience where the objects that we can experience around us with the unaided eye vary in size from items about the size of a flea or grain of sand to mountain ranges, and where experiences occur over seconds to tens of years. That's the scale we live on, and the one at which life manifests and meaning and purpose arise. If you strip that away, what remains is pretty meaningless regarding daily life.
Science informs us of much smaller and much larger scales, the scales at which we are a hive of buzzing subatomic particles interacting at the scale of nanoseconds, with no evidence of life or meaning in a human sense, and the scale of the very large, clusters of galaxies and billions of years, which is also outside of direct experience, offers no evidence of life, and as you suggest, is devoid of purpose. At that scale, earth is a mote with no sign of life as you suggest.
There is a common expression, "In the grand scheme of things, we are nothing but [add your own ending]." Well, we don't live at that scale. A holistic understanding of man and his place in the universe entails an awareness of all three scales, with only the normoscopic one (my word, to distinguish it from the larger macropscopic and the smaller microscopic realms) relating to daily life and what we call the meaning or purpose of our lives. It's a fallacy to reduce life to one of the less relevant scales and define man by that alone.
The microscopic counterpart of the fallacy of scale would be some variation of "If all we are is a soup of chemicals (or atoms in a void) ..." which is the logical equivalent of saying that the works of Shakespeare are nothing but letters, punctuation, and spaces.
