Because of archeological findings
The biblical timeline can be reinforced by the dates given in unprejudiced archeological reports.
Over and over, archeologists find that Biblical events really happened and that the dates match the Biblical timelines.
Here’s one I ran across recently [it's old news by now]:
Egyptian Chariots found under the Red Sea
You know the story. Pharoah finally let the Jews go when God killed his oldest son. Imagine! It took that much to get through his thick skull that God was serious. And it didn’t work for long, because the Pharoah took off to kill and recapture his slaves. God opened a way of escape through and across the Red Sea on dry land. When the Pharoah’s chariots tried to chase them across the sea, the sea returned to its bed and drowned them all. [Read Exodus 14]
Then Moses raised his hand over the sea, and the Lord opened up a path through the water with a strong east wind. The wind blew all that night, turning the seabed into dry land. So the people of Israel walked through the middle of the sea on dry ground, with walls of water on each side!
Then the Egyptians—all of Pharaoh’s horses, chariots, and charioteers—chased them into the middle of the sea. But just before dawn the Lord looked down on the Egyptian army from the pillar of fire and cloud, and he threw their forces into total confusion. He twisted their chariot wheels, making their chariots difficult to drive. “Let’s get out of here—away from these Israelites!” the Egyptians shouted. “The Lord is fighting for them against Egypt!”
When all the Israelites had reached the other side, the Lord said to Moses, “Raise your hand over the sea again. Then the waters will rush back and cover the Egyptians and their chariots and charioteers.” So as the sun began to rise, Moses raised his hand over the sea, and the water rushed back into its usual place. The Egyptians tried to escape, but the Lord swept them into the sea. Then the waters returned and covered all the chariots and charioteers—the entire army of Pharaoh. Of all the Egyptians who had chased the Israelites into the sea, not a single one survived. But the people of Israel had walked through the middle of the sea on dry ground, as the water stood up like a wall on both sides. That is how the Lord rescued Israel from the hand of the Egyptians that day. And the Israelites saw the bodies of the Egyptians washed up on the seashore. [Exodus 14: 21-30 NLT]
It looks like scripture is vindicated again…
The rest of the Red Sea at this point is thousands of feet deep. Here it is a gradual slope down and back up to the shores of Midian 10 miles across the waters. it really happened people