I am interested in science that can explain why we exsist, the cause either for or against a divine entity being irrelevant imho.
As it stands humanity is unable to answer definitivley why matter exsists or even really how the universe came into being, religion is the attempt of early civilizations to understand the world and answer the questions that as of yet still remain unanswered, either by religion or science. (If you want to define matter go get a dictionary!)
Time is a system of human quantification to describe the universe from one moment to the next, nothing more or less.
Infinity is a mathematical concept for a number(or something else) without end, start counting now every second of everyday, of every year and when you die you still will not have reached 'inifinity'. (an undefinably great or large amount.)
i'm not a biologist but the human consciousness is for lack of a better explanation imho " the state of being aware of ones own; thoughts, feelings, surroundings, and existance."
So on the whole whether you are a theist, atheist or agnostic no one can explain existance. All that humanity possesses are theories on how we and the rest of the universe came to exist.(Be they a religious theory or Scientific one.) As it stands we do exist and so does the universe.
How&Why we came to exist are unknown to us.
We don't know if god exists, or if it created everything however, we don't know if it did either.
In the end your orginal statement is flawed. Atheism is the non-belief in a higher power. An Atheists knowledge of the universe is limited to the collective knowledge of the rest of humanity and therefore cannot explain existance.
As NO one can explain existance. Yet. ( At least not in the ways you are asking

)
Please try not to make statements that are irrefutable. Atheists cannot explain existance, neither can theists or anyone else so attributing a lack of explanation soley to a single group/person is short sighted and naive. Especially when the question to which you want an answer to has been unanswerable by anyone in the whole of human history. As it stands humanity has defined the things matter, time etc.. but has no concrete information as to why they exist, knowing what something is and being able to give reasons for its existance are two entirely different questions. You maybe able to answer one but, not the other as in the above instances.
~element
Everything above is prefaced with imho.