apt update failed with missing key
Reading package lists... Done
Building dependency tree
Reading state information... Done
4 packages can be upgraded. Run 'apt list --upgradable' to see them.
W: An error occurred during the signature verification. The repository is not updated and the previous index files wil
l be used. GPG error: http://dl.google.com/linux/earth/deb stable Release: The following signatures couldn't be verifi
ed because the public key is not available: NO_PUBKEY 1397BC53640DB551
W: Failed to fetch http://dl.google.com/linux/earth/deb...le/Release.gpg The following signatures couldn't be
verified because the public key is not available: NO_PUBKEY 1397BC53640DB551
W: Some index files failed to download. They have been ignored, or old ones used instead.
Building dependency tree
Reading state information... Done
4 packages can be upgraded. Run 'apt list --upgradable' to see them.
W: An error occurred during the signature verification. The repository is not updated and the previous index files wil
l be used. GPG error: http://dl.google.com/linux/earth/deb stable Release: The following signatures couldn't be verifi
ed because the public key is not available: NO_PUBKEY 1397BC53640DB551
W: Failed to fetch http://dl.google.com/linux/earth/deb...le/Release.gpg The following signatures couldn't be
verified because the public key is not available: NO_PUBKEY 1397BC53640DB551
W: Some index files failed to download. They have been ignored, or old ones used instead.
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 1397BC53640DB551
the update command completed normally and the four packages installed without problems.