Is There Life on Mars?

Overview

One of the most profound questions in science is whether life exists or ever existed beyond Earth. Mars is the prime candidate in our solar system. In this lesson, students learn what conditions life requires, discover extreme organisms on Earth that thrive in Mars-like environments, and analyze real evidence to construct a scientific argument about the possibility of Martian life.

Background for Teachers

The search for life on Mars has driven planetary exploration for decades. Key concepts:

Requirements for life (as we know it):

• Liquid water (past or present)
• Energy source (sunlight or chemical energy)
• Organic molecules (carbon-based building blocks)
• Stable environment (protection from extreme radiation)

Extremophiles are organisms on Earth that thrive in conditions once thought impossible for life:

• Thermophiles live in boiling hot springs (Yellowstone)
• Psychrophiles survive in Antarctic ice
• Acidophiles live in extremely acidic environments
• Radiation-resistant organisms like Deinococcus radiodurans survive radiation levels hundreds of times what would be fatal to humans

Mars evidence:

• Liquid water existed on the surface billions of years ago (confirmed by multiple rovers and orbiters)
• Organic molecules have been detected by Curiosity rover in Gale Crater
• Methane has been detected in the atmosphere (on Earth, most methane is produced by living organisms, though geological processes can also produce it)
• Subsurface environments may still have liquid water today

No definitive evidence of life on Mars has been found yet, but the search continues with missions like Perseverance, which is collecting rock samples for return to Earth.

Lesson Procedure

Warm-Up: What Does Life Need? (10 minutes)

1. Ask students: “What do you need to stay alive?” Record responses (water, food, air, shelter, warmth).
2. Narrow the focus: “Scientists studying other planets look for three main things: liquid water, energy, and organic molecules — the building blocks of life.”
3. Pose the driving question: “Could Mars have — or have had — what life needs?”

Extremophiles: Life Finds a Way (15 minutes)

1. Introduce extremophiles: organisms that live in Earth environments that seem impossibly harsh.

2. Present 3-4 examples with images:

   • Tardigrades (water bears): survive extreme cold, heat, radiation, and even the vacuum of space
   • Bacteria in Antarctic ice: metabolize in temperatures well below freezing
   • Organisms in Yellowstone hot springs: thrive in boiling, acidic water
   • Rock-dwelling bacteria (endoliths): live inside rocks in the Atacama Desert, the driest place on Earth

3. Connection: “If life can survive in these extreme places on Earth, maybe it could survive — or once survived — in similar environments on Mars.”

4. Students examine microscope slides or detailed images of extremophiles, sketching what they observe.

Evidence Analysis: Mars Habitability (20 minutes)

Provide student groups with “Mars Evidence Cards” — each card presents one piece of real evidence:

1. Ancient River Valleys: “Satellite images show branching channels that look exactly like dried river beds on Earth.”
2. Clay Minerals: “Curiosity rover found clay minerals that only form in the presence of water.”
3. Organic Molecules: “Curiosity detected organic (carbon-containing) molecules in Martian rocks.”
4. Methane Detection: “Scientists have measured methane gas in Mars’s atmosphere. On Earth, most methane comes from living things.”
5. Radiation: “Mars’s thin atmosphere lets through much more harmful radiation than Earth’s.”
6. Temperature: “Mars surface temperatures average about -60 degrees Celsius (-80 degrees Fahrenheit).”

Students sort cards into three categories:

• Supports life (evidence that life could or did exist)
• Challenges life (evidence that makes life difficult)
• Needs more investigation

Claim-Evidence-Reasoning (10 minutes)

Students complete a CER (Claim-Evidence-Reasoning) worksheet:

• Claim: “I think life [could / could not / might have] existed on Mars because…”
• Evidence: cite at least two evidence cards
• Reasoning: explain how the evidence supports the claim

Emphasize: there is no single “right answer” yet — this is an active area of scientific research!

Wrap-Up (5 minutes)

1. Share 2-3 student CER arguments. Note how different students may reach different conclusions from the same evidence — that is how science works!
2. Share: “NASA’s Perseverance rover is right now collecting rock samples from Mars. Those samples will be brought back to Earth so scientists can study them with the most powerful instruments we have. We may find the answer within your lifetime!”
3. Reflect: “Why does it matter whether life exists on Mars?”

Assessment

• Evidence card sorting: Demonstrates ability to evaluate scientific evidence
• CER worksheet: Claim is supported by cited evidence with logical reasoning
• Discussion: Students can explain why the search for life on Mars is scientifically important

NGSS Alignment

• 5-ESS1-1: Support an argument that the apparent brightness of the sun and stars is related to their relative distances from Earth
• 5-LS1-1: Support an argument that plants get the materials they need for growth chiefly from air and water
• 5-PS1-1: Develop a model to describe that matter is made of particles too small to be seen (connection to molecular biosignatures)
• 3-5-ETS1-3: Plan and carry out fair tests in which variables are controlled and failure points are considered to identify aspects of a model or prototype that can be improved

Extensions

• Research the Mars Sample Return mission — when will the Perseverance samples reach Earth?
• Design an experiment to test whether a specific extremophile could survive Mars surface conditions
• Debate: “Should we send humans or robots to search for life on Mars?” with evidence-based arguments
• Read about the ALH84001 meteorite — a Mars rock found in Antarctica that some scientists believed contained fossil bacteria