Lesson 2: What is Life?
Key Learning Objectives:
Appreciate the difficulties scientists face when trying to define life.
Identify key essential components of life.
In this lesson you'll find...
Defining Life
Requirements for Life
Scientific Debate and Ongoing Research
Defining Life
In our exciting quest for finding life beyond Earth, defining what life is exactly and what elements are essential for life to develop becomes a little complicated. While Earth provides our only template for life, the vast diversity of potential exoplanetary environments prompts us to reconsider the boundaries of what life could be. Life might transcend our conventional notions, adapting to environments vastly different from our own. It beckons us to ponder whether life could thrive in exotic forms, perhaps dwelling in the subsurface oceans of icy moons or existing as ethereal, atmospheric entities.
Class Discussion
How would you define life and what do you think are the essentials for life to thrive?
This is actually an extremely complicated question and an active topic of scientific debate! The NASA definition for life is that "Life is a self-sustaining chemical system capable of Darwinian evolution" Do you agree with this definition or do you think it is missing something?
Requirements for Life
As we discussed in the previous lesson, scientists are focussing on finding water-based life, even though we acknowledge that it may be possible for other forms of life to exist. Essentially, we can only start looking for life that is similar to our own since we understand the specific set of conditions that must be met for our type of life to thrive.
Life as we know it here on Earth generally requires:
Liquid Water: Water is a universal solvent and a crucial medium for biochemical reactions. Life on Earth is intimately tied to the presence of liquid water.
Chemical Building Blocks: Life relies on specific chemical elements, including carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur (CHNOPS). These elements form the molecular basis of biological macromolecules like proteins, nucleic acids, and lipids.
Energy Source: Living organisms need an energy source to drive metabolic processes. On Earth, the primary energy source is the Sun, which fuels photosynthesis, but some extremophiles derive energy from geothermal sources.
Stable Environment: Life generally thrives within a certain range of environmental conditions, including temperature, pressure, and pH. While extremophiles can survive in extreme conditions, most life on Earth prefers relatively stable environments.
Protective Atmosphere: Earth's atmosphere provides a protective shield against harmful solar radiation and stabilises surface temperatures. The presence of an atmosphere can be crucial for maintaining conditions conducive to life.
These requirements are based on our understanding of life on Earth, and they serve as a starting point for the search for habitable environments on other planets and moons. However, as scientists explore the possibilities of life beyond Earth, they remain open to the idea that life could potentially exist under different conditions and with different biochemical foundations.
Have a look at the video below from 0:00 to 3:13. Can you appreciate the interconnection between physics, chemistry, and biology when definign life?
Scientific Debate and Ongoing Research
The definition, requirements and origins of life are major ongoing debates within the scientific community with no one answer universally accepted. As a scientifically-educated citizen in today's technological age, you are empowered to explore the diversity of opinions and draw your own conclusions!
Activity
Read one of the articles below and complete the following tasks:
Summarise each paragraph of the article in one sentence.
Identify two key points (take-home messages) from the article.
Identify a chemistry-related concept from the article.
Create a tweet (about 2 sentences) to share with your class that captures the essence of the artcile you read.
