Multiple alien species on Earth at the same time: one species destroys Earth but the other preserves a small group of humans

Question

Summary:

An alien craft lands, it's referred to by one scientist as a "cinder cone", an alien representative comes out and talks to humanity, but it was all a delay tactic. It was later discovered during an autopsy after this alien died of apparent natural causes that it looked as if the creature was not "designed" for a long life...it was possibly manufactured to talk to humans.

Meanwhile other alien craft had descended into the oceans and huge amounts of oxygen were rising up from the sea. It was later discovered they were making atomic bombs and planting them all along the tectonic plates. Another species of alien was on Earth at the same time and had dispatched untold numbers of tiny robots which were seen by scientists in the story conducting research on life on earth to preserve as much knowledge about life here as possible, specifically in one instance one was dissecting a bird. Just before the bombs were set off, causing the plates to tilt up and be swallowed by the core killing all life on Earth, the second group of aliens gathered a small group of humans and gave them their own interstellar ship, not to save them but to give them the opportunity to seek out the race that destroyed Earth.

They did find it later and discovered this race sent out ships to planets with life in order to kill that life, so there would be less competition for resources in the universe!

I think there may have been more books later, making it a short series, but I only read this one. I read it back in high school in the 1980s. I think it was written in the early 1980s or even in the 1970s.

Answer 1

The Forge of God by Greg Bear, from 1987.

From the wiki page:

The novel features scenes and events, including the discovery of a nearly-dead alien in the desert, who clearly says in English, "I'm sorry, but there is bad news," and the alien's subsequent interrogation and autopsy; the discovery of an artificial geological formation and its subsequent nuclear destruction by a desperate military; and the Earth's eventual destruction by the mutual annihilation of a piece of neutronium and a piece of antineutronium dropped into Earth's core.

There is another alien faction at work, however, represented on Earth by small spider-like robots that recruit human agents through some form of mind control. They frantically collect all the human data, biological records, tissue samples, seeds, and DNA from the biosphere that they can and evacuate a handful of people from Earth. In outer space, this faction's machines combat and eventually destroy the attackers but not before Earth's fate is sealed. The evacuees eventually settle a newly terraformed Mars while some form the crew of a Ship of the Law to hunt down the home world of the killers, a quest described in the sequel, Anvil of Stars.

The spaceships is repeatedly referred to as being disguised as a 'cinder cone'.

"Shut up," Edward said.

"That cinder cone's a spaceship, or a spaceship is buried underneath, obviously—" Minelli blurted.

"Nothing's obvious," Reslaw said calmly.

"I saw that in It Came From Outer Space"