One of the biggest events in Earth's four billion year history is the oxygenation of its atmosphere. Around two and a half billion year...

An upper bound can be generated somewhat easily. The sun continues to grow larger and larger, and one day it will become so large, in what ...

Since there are no signatures, at least bold, obvious ones, that there was a large, ancient civilization before our era, the possibility of ...

It seems fairly clear that if there was an ancient civilization, in the era of ten to twenty thousand years ago, it had a low population. I...

When we think about the existence, ten or twenty thousand years ago, of an ancient civilization and ask what signs might be left behind, we ...

You can walk around in monuments two thousand years old in Egypt. Archaeologists dig up mounds with relics from five thousand years ago. I...

Asking the question about whether there could have been a more advanced civilization of humans that was eliminated in a catastrophe, or rela...

Common belief here on Earth is that our civilization has been continuously improving since the human species came into existence. It has be...

Aliens haven't visited us as far as we can tell. They also haven't sent us messages that we could recognize. So, we have to peer o...

Can an alien civilization arise in a binary star system? This is not a relevant follow-on question to the principal one: Why haven't al...

Currently, it is very hard for Earth astronomers to detect black holes. Black holes are neutron stars which have enough mass to generate a ...

One question relating to the geological separation of useful mineral ores on exo-planets, something critical for an alien species to develop...