Topic 8.8: The Search for Life

Is there life beyond Earth? The honest answer today is: nobody knows. No life, not even a microbe, has been confirmed anywhere except on Earth. The search is one of the most exciting questions in science, so it is worth knowing how it is done and how careful scientists have to be.

What Life Seems to Need

Every living thing we know about needs three things:

1. Liquid water, as a place for chemistry to happen.
2. An energy source, such as sunlight or chemical energy.
3. The right chemistry: carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur and other elements.

Scientists search for these things. Of course, other kinds of life might be possible, but we do not yet know how to look for something we do not understand.

Where Scientists Are Looking

• Mars. Billions of years ago, by the standard timeline, Mars had rivers and lakes. Perseverance is exploring an ancient river delta in Jezero Crater and collecting rock samples to be returned to Earth. In 2024 it found a rock with unusual spots that might have a biological origin, or might not.
• Europa and Enceladus. Both moons seem to have salty oceans under the ice, with a source of heat and chemicals. Enceladus's geysers contain water, salts and simple organic molecules (Topic 4.8). Europa Clipper will study Europa in the 2030s.
• Titan. Lakes of liquid methane, and an atmosphere rich in organic chemicals. Any life there would be very different from ours.
• Exoplanets. The Webb telescope looks at the air of planets in habitable zones for biosignatures (gases that life might make), such as oxygen together with methane. So far claims, such as a report of dimethyl sulfide on K2-18b, have been disputed.

Listening: SETI

SETI (the Search for Extraterrestrial Intelligence) listens for radio or laser signals that nature could not make.

• 1960: Frank Drake's Project Ozma listened to two stars.
• 1974: Scientists sent the Arecibo message toward a star cluster, 25,000 light-years away.
• 1977: the "Wow!" signal, a strong radio burst that was never heard again and was never explained.
• Today: projects like Breakthrough Listen scan millions of stars.

The Drake equation is a way of organizing our ignorance. It multiplies factors such as the number of stars, the fraction with planets, the fraction of those where life starts, and so on. Some of the factors we know fairly well now (planets are common); the key ones (how likely it is that life starts at all) are completely unknown. The answer can be anything from "we are alone" to "the galaxy is crowded."

Careful Claims

In 1996, NASA scientists announced that a meteorite from Mars (ALH84001) contained possible fossil microbes. After years of study most scientists concluded that non-living processes could explain the shapes. In 2020, phosphine was reported on Venus; that claim is also disputed. This is how science should work: bold claims need strong evidence, and extraordinary claims need more.

An Important Fact

Nobody has ever made life from non-living chemicals, in the lab or by any known natural process. This is called the origin-of-life problem. Scientists have made some of the building blocks (amino acids, sugars, some RNA parts), but not a living cell. How life began remains an unsolved question. If life is found elsewhere, it will tell us something about how common it is; it will not by itself tell us how it began.

Christians and Life Elsewhere

Christians hold a range of views. Many say that finding microbes on Mars or Europa would not threaten their faith at all: "The earth is the LORD'S, and the fulness thereof" (Psalm 24:1), and if He made life in other places, that would simply show more of His generosity. Some stress that the Bible says nothing about life elsewhere, and others, such as the authors of Rare Earth and The Privileged Planet, have argued that Earth is special in ways that make complex life very rare. A fair summary: the Bible neither promises nor rules out life elsewhere, and a careful Christian can look at the evidence with curiosity.

Worth a Pause

The Gospel of John says of the Word, "All things were made by him; and without him was not any thing made that was made. In him was life; and the life was the light of men" (John 1:3-4). However the search ends, with microbes in an ocean under the ice, with a signal from a distant star, or with decades of silence, that verse still marks where a Christian starts: life is a gift, not an accident of chemistry that we can explain away. We are looking for neighbors, and it is good to look. But we already know where we got our own life from. The video talks about life evolving in oceans on other worlds. That is a theory built on a bigger theory. The honest fact is that nobody has made life from non-living matter, and nobody has found life beyond Earth. Ask what about creation: if life is only chemistry, why can't we make it, and who gave life to the first living thing?

Practice Problems

1. What three things does life as we know it seem to need?
2. Name two places in the solar system where scientists are looking for signs of life and say why.
3. What is a biosignature?
4. What was the 'Wow!' signal?
5. Why did most scientists doubt the claim of fossil microbes in the Mars meteorite ALH84001?
6. Has life ever been made from non-living chemicals? What is this problem called?
7. What do Christians believe about life elsewhere, according to this lesson?