A spacecraft could plunge into Earth’s atmosphere as soon as Tuesday. While most of the probe will likely burn up during reentry, a few components are expected to survive.

Scientists are trying to understand how complex life emerged on Earth about 2 billion years ago. Our microbial ancestors could be the key.

Picture all of Earth’s oceans, which cover about 70% of the planet and are mostly made of hydrogen. Now multiply that by nine. That may be the amount of hydrogen in Earth’s core, possibly making it ...