Was the Earth so cold at some points in its history that all surface water froze solid?

During certain periods in the Earth's history, particularly during what is known as the Snowball Earth hypothesis, it is theorized that the Earth experienced extreme glaciation, where the entire planet's surface water could have frozen solid. This scenario is believed to have occurred during two main periods: the late Proterozoic era, around 600 million years ago, and possibly during other glacial periods.

The Snowball Earth theory suggests that the combination of low atmospheric CO2 levels and other climatic factors led to such drastic cooling that the equatorial regions experienced ice cover. This would have resulted in the surface temperatures dropping significantly enough to freeze ocean waters. Such conditions would have profoundly impacted the planet's climate system, ocean circulation, and life on Earth.

Understanding this concept is crucial, as it highlights the dynamic nature of Earth's climate and how it has shifted between extreme warm periods and intense ice ages. Recognizing these historical facts helps illustrate the potential vulnerability of our current climate in the face of ongoing changes.