How would life on earth change if Earth's gravity changed?

Answer 1

There is a whole book to be written speculating about how life would be if Earth's gravity was weaker or stronger. Let's assume weaker gravity for this discussion - whatever applies to weaker gravity probably applies in reverse for stronger gravity.

The most obvious effect of weaker gravity on higher animals is that they could be larger. The largest land animals are, in part, limited in their size by the strength of the bones in their legs, and in the ability of their bodies to deal with gravity (for example, in simply holding the internal organs in place). With weaker gravity, bones that are made in the same way as those in existing animals could hold up much greater weights, so animals could be truly enormous by our standards.

However, like anything in science, there are details that we would also have to consider that could change things considerably. Lower gravity could mean that lighter gases could escape Earth's atmosphere into space (as hydrogen and helium do now), changing our atmosphere in ways that we might not expect. The effects could be higher or lower temperatures, the formation of lower or higher amounts of ozone in the ozone layer that could increase or decrease damaging UV radiation from the sun, or even a requirement for living creatures to exist in a reducing atmosphere - the opposite of the oxidising atmosphere that we have now, and more like the atmosphere of the early earth.

Other effects would result from the physical form of the Earth - lower gravity would mean higher mountains and so probably a wider variety of ecological environments, different coverage of the Earth with water, etc.

In short, the differences could be very significant, and probably unpredictable - and the ones that are given here are just for starters.

Answer 2

If Earth's gravity decreased significantly, things like muscle strength, bone density, and overall physical health in humans and animals may be affected. Plant growth and ecosystems could also be disrupted as plants rely on gravity for roots to grow and for water to be pulled up through their stems. Conversely, if Earth's gravity increased, it could impact flight, making it harder for birds and insects to stay airborne, as well as pull ocean water higher up Coastlines.