How old is the Earth? Most people and virtually all scientists say that it is 4.5 billion years old, but some still claim that the Earth is just 10,000 years old, and even more incredible some actually claim it is half that age!
People that make such outrageous arguments that I have encountered ignore all physical sciences which easily debunks said arguments. One of the more humorous arguments is the moon dust young earth argument which says that the moon should be covered in about 100 feet of interstellar dust. But it has been known since the 1960's that this is false because the moon only receives one percent of the interstellar dust creationists claimed because of the solar wind from our sun deflects most of it.
(Young Earth Argument: Moon Dust - http://www.don-lindsay-archive.org/creation/moondust.html )
Additionally of course there is the problem with the fact that human made structures have been found older than the young earth theories (archeological finds in Europe date back 14,000 years for instance) and carbon dating confirms the vast age of the earth. Additionally light from stars billions of years away reaches the world which wouldn't be possible if the universe was as young as some say.
Finally the existence of dinosaurs in the same time period as primitive humans would have obviously resulted in human extinction. Even today humans would face a serious threat if fast, intelligent, and ferocious dinosaurs like the T-Rex or velsorapter suddenly appeared, even with the weapons of today it would be a serious challenge. With rocks and sticks humans wouldn't stand a chance against titan superpredators like the spinosauros egyptis which roamed Africa and the Middle East where early (Biblical) humanity thrived. Clearly they existed in the far past tens of millions of years before humans, and the earth is billions of years old.