Young-Earth creationists (YECs) believe that God created the Earth and all life on it in six 24-hour days, exactly as described in Genesis, and that the universe (and by extension the Earth) is less than 10,000 years old. These YEC claims contradict a number established scientific and historical precepts.
Scientific difficulties with Young Earth Creationism
Cosmology and astronomy
Speed of Light
One problem with Young Earth Creationism is with light. Supposedly, according to Young-Earth Creationists, the universe is 10,000 years old. Since light travels in light years, we would only be able to see stars that are less than 10,000 light years away. The Great Andromeda Galaxy is 2 million light years away. Other galaxies are even further away. Scientists have seen stars that are at least 13 billion light years away from the Earth. If the universe was only 10,000 years old, the light from these objects would not be able to be seen by telescopes.
The formation, lifecycle and end of stars is broadly understood by scientists. Observable stars are seen at all stages of the stellar lifecycle. If the universe was very young, stars would be of the same age. Also, individual stars would take billions of years to reach their current state: our sun is 4.6 billion years old. 
Modern cosmology has established that the universe as we know it is about 13.7 billion years old. This is, by far, much older than what creationists say. This age estimate is largely based on the immense distance of our galaxies and their speed they are moving away. The evidence consistently correlates with the model of the Big Bang.
Age of Earth
One topic that comes up frequently is the age of Earth. Young-Earth creationists believe that Earth is about 6,000-10,000 years old. This contrasts with radiometric dating of the Earth, which puts its age at 4.6 billion years. Rocks from space also have been dated around 4.6 billion years. Geologists also track changes in the Earth happening over millions of years, such as plate tectonics and mountain building. Other signs the Earth is ancient include:
- Fossil remains and artifacts in the Americas show that humanity migrated to the Americas thousands of years before Young-Earth creationists believe when the Earth was created. Does the biblical textual evidence outweigh physical evidence? In the opinion of Bible literalists it aparently does, even though the bible says pi is 3, bats are birds, whales are fish and that displaying striped patterns to a pregnant cow will make it give birth to striped cats (the bible is, under no context a valid scientific resource.).
- Charles Darwin argued that a thick layer of chalk located in south east England, known as the Weald of Kent, must have taken hundreds of millions of years to be eroded into its current shape. Geologists now think erosion of the layer began about 65 million years ago, when the rocks were uplifted. 
- Near the south pole, ice layers are deposited during the annual cycle of seasons. By drilling through the ice, a series of layers is revealed. The deepest ice cores have seasonal layers for at least 800,000 years. 
- The east coast of South America and the west coast of Africa have a striking similar shape. This was thought to be a coincidence until similar types of rocks and similar fossils were found along the split, suggesting the land was once connected. Geologists now think this split occurred 130 million years ago. The South American Plate is still moving westward at 10 cm/year! 
- Evolution, for which overwhelming evidence has been found, would take billions of years to produce complex multi-cellular organisms.
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- ↑ In the Footsteps of Time: Geology and Landscape of Cuckmere Valley and Downs By Monty Larkin
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