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Life on Mars - Background
This lesson is built around the discovery of Martian “blueberries” by the rover Opportunity in Meridiani Planum. The blueberries aren’t really blue – they’re actually grey – nor are they the size of blueberries – they are only around 3 millimeters in diameter. When they were first observed scattered across the floor of Meridiani Planum, their composition was an enticing mystery.
What are they? Their uniformity and symmetrical shape calls to mind the bacterial and fungal colonies grown on agar plates. Could they once have been living things, now frozen or fossilized on the surface of Mars? What about the 3 fused berries in the picture? Does this capture the process by which berries reproduce? That is the question posed to students in this activity, however, this is not a theory supported by scientists. Scientists guessed that the blueberries were concretions, formed when water rich in minerals permeates into porous rock then evaporates, leaving behind the hardened minerals in the spaces. Although originally buried within the rock, as the surrounding rock weathered away, the concretions were freed and left to roll around on the Martian surface.
For several long weeks, the blueberries were too small and scattered to be analyzed accurately with Opportunity’s scientific instruments. Thus the scientists’ theory could not be confirmed. Finally the rover reached a spot nicknamed the “Berry Bowl”. There, enough blueberries had collected in one place for the rover to use its Mössbauer, thermal emission, and alpha particle X-ray spectrometers to decipher its chemical make-up. By comparing the berry cluster in the Berry Bowl with a berry-free patch nearby, scientists were able to determine that the blueberries are composed of hematite (or haematite).
Hematite is the mineral form of iron oxide (rust). It is very common on Earth and is generally found in places where there has been standing water or mineral hot springs. However, it may also be formed volcanically. So, does the hematite blueberries on Mars indicate the former presence of water or were the blueberries formed volcanically? The presence of fused blueberries, like the triplet berry near the center of the image strongly argues that these blueberries were formed through the action of liquid water. Volcanically formed beads are unlikely to fuse along a line in this fashion.
More information on the Mars Exploration Rover mission is available on the NASA/JPL website and specific links of interest to this lesson are provided in the Sources section.
Tips for Teachers
The yeast will remain active when added to the nutrient milkshake for a few hours until they run out of nutrients to sustain their growth. Adding more milkshake will reinvigorate the culture.
For students to grow yeast on agar plates, the nutrient agar must include sugars for the yeast to digest. This differs from the agar plates described in the Life Trap activity in which no sugar was required. In addition, it is best to dissolve the yeast-soil sample in water first (approximately 1 part yeast-soil to 2 parts water) and seed the plates with a Q tip dipped in the solution. Dry yeast get too little moisture from the plates alone to grow effectively.
To test for organic molecules, it is important to dissolve the yeast-soil sample in water first (approximately 1 part yeast-soil to 2 parts water). Only the protein test will yield a positive result. If you want to increase the rate of positive results, add 2 tablespoons of flour to the yeast-soil mixture. This will make the starch test give a positive result as well without interfering with any of the other tests the students might conduct.