<human>:  When did the first lava flow from a volcano?
<bot>: The first lava flow from a volcano was probably about a billion years ago. Lava is molten rock that comes from the interior of the earth. The first lava flows were probably from the earth’s mantle, which is the layer between the crust and the core of the earth. The mantle is a region of the earth that is hot enough to melt rocks.