Why is alien life not so easy to find?

“Life depends on more than just water; it also requires a delicate chemical balance established during a planet’s earliest moments. New research suggests that Earth’s ability to support life may hinge on an exceptionally narrow window of oxygen conditions during core formation, allowing both phosphorus and nitrogen to remain accessible. Credit: SciTechDaily.com” (ScitechDaily, Life Needs More Than Water: The Missing Clue Scientists Just Discovered)

Alien life would be like lifeforms on Earth. If we think about the chemical processes behind those creatures. If alien life forms are based on a similar chemistry to life on Earth. That means there must also be other life building blocks than just water. One of the most critical chemicals. Or an element on alien lifeforms. Is phosphorus. And another critical element is nitrogen. Phosphorus is needed. In RNA and DNA formation. And nitrogen is needed for proteins. 

Without those two elements, DNA and cell-membrane proteins cannot form. There must be so much free nitrogen that those chemical compounds can form. Another thing is that if the phosphorus interacts with iron too early, that means it falls into the planet’s core. Another possibility is that. If phosphorus reacts with oxygen. That means it loses its ability to form compounds in RNA and DNA. 

“Young rocky planets begin as roiling oceans of molten rock. As gravity pulls materials into layers, dense metals such as iron sink inward to form the core, while lighter material remains above to become the mantle and, later, the crust. That physical separation is only half the story. At the same time, chemistry is deciding which elements prefer metal and which prefer rock, and oxygen is one of the biggest drivers of that choice.” /ScitechDaily, Life Needs More Than Water: The Missing Clue Scientists Just Discovered)

“If oxygen is scarce during core formation, phosphorus tends to bond with iron and other heavy metals and is dragged down into the core. Once that happens, it is effectively removed from the surface environment where life would need it. If oxygen is too abundant, phosphorus stays in the mantle, but nitrogen becomes more likely to escape into the atmosphere and eventually be lost. In other words, the conditions that protect one life's essential elements can make the other harder to keep.” (ScitechDaily, Life Needs More Than Water: The Missing Clue Scientists Just Discovered)

The environmental stability means that nitrogen and phosphorus must react with the right elements. And that reaction requires that those elements have free points that can touch the right chemicals. If phosphorus reacts with oxygen, that means the phosphorus turns into phosphorus trioxide. Or phosphorus pentoxide. The last compound is an important actor in organic synthesis. 

https://scitechdaily.com/life-needs-more-than-water-the-missing-clue-scientists-just-discovered/

https://en.wikipedia.org/wiki/Phosphorus_pentoxide