Geologist Trophy in Lifeless Planet

Science samples will look like little plants on the ground. They won't always look the same as they come in different colors. They can be found in various places throughout the levels. When you get close to one it will have a white shine on it indicating that it's a collectible. There are a few more than the 15 that are required for this trophy. These science samples are more out of the way than the documents (see Planetary Historian).

If you haven't obtained this trophy by the time you've gotten every other trophy, you can use chapter select and pick up the collectibles that way.