Initially believed to be a cold, arid grassland, the stretch more resembled the modern-day Yukon-Kuskokwim floodplain.

It's even visible from space. Scientists issue warning over bizarre phenomenon spotted in Alaskan rivers: 'Have to be stained a lot...' first appeared on The Cool Down.

Invasive species can disrupt or destroy habitat and food supplies for native animals and plants which can ripple out to ...