Over the years, there have been many attempts by secular sources to ascribe natural explanations to certain miracles in the Bible. A few notable examples surround the 10 Plagues of Egypt (Exodus 7-11) and the Parting of the Red Sea (Exodus 14). In 1957, Greta Hort, a Dutch physicist published a “chain reaction” theory explaining how a massive amount of red algae and red clay in the Nile turned it “to blood,” which drove out the frogs, killed livestock, bred mosquitoes, and caused all the other plagues described in Exodus. A similar phenomenon occurs occasionally when describing New Testament events. For example, a few people attempt to explain the darkness at Jesus' crucifixion as an eclipse (an impossibility since the Passover occurs at the time of a full moon).
A few, well-meaning Christians have adopted Hort's explanation (and other, similar explanations) as “scientific evidence” supporting the Biblical account. However, the vast majority of these explanations are rejected by mainstream Christians. The 10 Plagues of Egypt were not natural events that merely coincided with God's judgment. They were supernatural events, intended not only to bring God's wrath on the Egyptians but also to demonstrate God's Lordship over nature and His superiority over the false gods of the Egyptians. The Egyptians worshiped the Nile; God turned the Nile to blood. The Egyptians worshiped the sun; God turned the sun black for three days.
This desire to appeal to natural explanations for miraculous events is curious. When a passage obviously refers to a miraculous event, why would any Christian seek a natural explanation instead? It's precisely because such an event defies a natural explanation that we know it's the work of God. If God only performed His miracles in the guise of a natural event, then God would be completely indistinguishable from dumb luck. He would seem to me to be a god of coincidences – a charlatan who exploits rare but mundane events as examples of his “power.”
Like I've said, the vast majority of these natural explanations are rejected by mainstream Christians. However, one natural explanation still endures and is accepted by a sizable percentage of Christians. It is the natural explanation of our origins. Why is it that many of the same Christians who reject ideas like Hort's, will embrace the Big Bang and evolutionary views of people like Hawking and Dawkins? It's a sort of special pleading. They will believe that Jesus literally turned water to wine but they refuse to believe God literally spoke and the universe appeared. It almost seems that they have too low an opinion of God where He is able to do “little” miracles in an instant but creating the universe must have taken billions of years!
What makes it especially odd is that Hort's views seem more plausible than the far fetched ideas like the Big Bang which proposes everything came from nothing. If I were to believe any natural explanation for a miracle, I'm sure I would be far more apt to believe the credible explanations. God creating life is far more credible and scientific than life simple appearing from a random mix of nonliving chemicals. What's odder still is how these Christians will reject the explanations that fit well with a plain reading of the text (like red algae and clay turning the Nile blood-red) but then resort to a tortured reading of the text to make it fit the natural explanation (like “day one” in Genesis 1 really means “billions of years”).
Why should I believe that some passages of the Bible describe miracles while other passages are merely fantastic descriptions of natural events? Why should I believe that the Hebrew children, who could understand that the parting of the Red Sea was a supernatural act of God, couldn't have also understood “millions of years” if God explained it to them? Why should I believe the supernatural explanation that God raised Jesus from the dead after 3 days and not the supernatural explanation that God created the world in 6 days? It all seems rather arbitrary to me. When critics pull tricks like this, I accuse them of special pleading. When Christians do it, I also call it special pleading.