What evidence is there that the Mayans existed in the timescale that we are told they did?
What evidence directly shows us their writings that show us they knew the full scale of Earth and the planets, etc?
The temples and pyramids they left behind.
The Temple of the Cross Complex. Tikal. Chichen Itza.The Chichen Itza was positioned according to the sun's position on the equinoxes of spring and fall. Pretty good proof they knew what they were doing.
Like many ancient civilizations they illustrated their beliefs and documented their histories in their places of worship. They actually had one of the first known written languages.
The Mayan calendar is proof they knew the full scale of Earth and the planets. They could accurately predict solar eclipses and moon cycles.
No evidence they ever believed in an ice dome though. So maybe they didn't know everything.