Scripture teaches us that God exists and that God created everything in the cosmos.
In the beginning, God created the heavens and the earth..."Let us make man in our image, after our likeness... (Gen. 1:1, 26)
According to scripture, the atheist is also in the image and likeness of God. Whatever he may say about the world, he is still a human being created specifically to mirror the God who created him. He is an image, a likeness of God.
Scripture also teaches us that all creation gives evidence for God's existence.
The heavens are telling the glory of God: and the firmament proclaims his handiwork. (Psalm. 19:1)
Ever since the creation of the world his invisible nature, namely his eternal power and deity, has been clearly perceived in the things that have been made. (Romans 1:20)
It makes basic intuitive sense to think that a building will evidence the existence of its builder, so it makes basic intuitive sense to think that if God created the heavens and the earth, then all creation would evidence God's existence.
That which is created speaks of its creator.
Take, for example, the book "God Is Not Great," written by the famous atheist Christopher Hitchens. We should be able to agree that Hitchens' book makes the case for the existence of Hitchens. The book speaks of the existence of its author in every way as well as revealing something of his nature, character and personality.
Imagine for a moment that someone denied that Hitchens wrote the book. Imagine this person claimed that the book called "God Is Not Great" was just the result of an explosion in a print factory or the book was simply the accidental result of random processes acting upon random collections of elements. Can you imagine anyone wasting any time pondering the possibility that Christopher Hitchins did not write the book, which just happens to bear his name on its cover and in its copyright statement and happens to have his picture on the dust cover?
As a book tells you much about its author, so it is with the stars and planets, oceans and forests, animals and plants, and especially human beings, speak about its creator. Each of them individually and all of them corporately speak to us of God's existence. And, through their beauty and order, they tell us a great deal about what kind of person he is.
For the wrath of God revealed from heaven against all ungodliness and unrighteousness of men, who suppress the truth in unrighteousoness, because that which may be known about God is evident within them; for God made it evident to them. For since the creation of the world His invisible attributes, His eternal pwerer and divine nature, have been clearly seen, being understood through what hs been made, so that they are without excuse. (Romans 1:18)