It's not accurate to say there was one single "new evidence" that discovered plate tectonics. Instead, it was the convergence of several lines of evidence, accumulated over decades, that built the foundation for this revolutionary theory. Here are some key pieces of evidence and their approximate discovery periods:

1. The Fit of Continents (Early 20th Century)

* Evidence: The remarkable fit of the coastlines of South America and Africa, especially at the continental shelf level, was noticed long before the theory of plate tectonics.

* Significance: This observation suggested that these continents were once joined, but it lacked a mechanism for how they could have moved apart.

2. Fossil Distribution (Early 20th Century)

* Evidence: Similar fossils of ancient plants and animals were found on continents now separated by vast oceans.

* Significance: This supported the idea of a once connected landmass and raised questions about how these organisms migrated across vast bodies of water.

3. Paleomagnetic Data (Mid-20th Century)

* Evidence: Studies of the magnetic properties of rocks revealed that the Earth's magnetic field has reversed its polarity many times throughout history.

* Significance: This led to the discovery of "magnetic stripes" on the ocean floor, symmetrical on either side of mid-ocean ridges. These stripes showed the movement of the ocean floor away from these ridges, providing crucial evidence for seafloor spreading.

4. Seafloor Spreading (1960s)

* Evidence: New technology like sonar mapping revealed the mid-ocean ridges, the rift valleys, and the magnetic stripes on the ocean floor.

* Significance: This provided the mechanism for continental drift - the movement of tectonic plates caused by the upwelling of magma at mid-ocean ridges.

5. Earthquake and Volcano Distribution (Ongoing)

* Evidence: The locations of earthquakes and volcanoes are not random, but rather clustered along specific lines, which coincide with the boundaries of tectonic plates.

* Significance: This further reinforced the idea of moving plates and their interactions.

The "Discovery" of Plate Tectonics

While some of these pieces of evidence were available earlier, the theory of plate tectonics really gained traction in the 1960s, with the combination of evidence from paleomagnetic data and seafloor spreading.

It's important to note that the concept of continental drift was proposed earlier by Alfred Wegener in the early 20th century. However, his theory lacked a strong enough mechanism for how the continents moved and faced significant opposition. The discovery of seafloor spreading provided the missing piece of the puzzle, paving the way for the acceptance of plate tectonics as the unifying theory for understanding Earth's geological processes.