Recent comments in /f/askscience

mfb- t1_jcsfrx5 wrote

Reply to We're often taught that objects travel to lower energy states to reach stability. But the energy of the universe is constant - doesn't that just mean other surrounding things go to higher energy states? What decides which thing gets to have low energy? by SMM-123Sam

The surrounding is often empty space which has a very low energy density and temperature, and its energy density and temperature keep decreasing as the universe expands. Dumping some energy into empty space isn't going to make a difference for space, but it means your object loses energy.

Total energy is not conserved in an expanding universe, by the way, but that's a smaller effect than the larger volume over which the energy is distributed.

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RadRiverOtter t1_jcseb4z wrote

Reply to comment by You_Stole_My_Hot_Dog in Why have many plants evolved to need nitrogen-rich soil, when there is so much nitrogen freely available in they air they use anyway? by runningchild

Just adding a little to this. Nitrogen is often the limiting factor in an ecosystem. Certain plants, mostly Legumes, evolved to form a symbiosis with rhyzoba bacteria that are able to convert gaseous nitrogen into usable NH3. These plants are generally "pioneer species"; popping up in disturbed or nitrogen deficient regions. Once these plants finish their life cycle and break down they increase the overall usable nitrogen in the ecosystem. More fascinating are the incredible traits that many taxa have evolved in adaptation to nitrogen deficient soils that don't use rhyzoba. One example being the several convergent carnivorous plants. Or plants that trick animals into defecating on them.

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