Brazilian geologists announced the discovery, 1,500 kilometers (900 miles) from Rio, of what could be part of the continent that was submerged when the Atlantic Ocean was formed as Africa and South America drifted apart 100 million years ago.
Roberto Ventura Santos, a top official at Brazil's Geology Service (CPRM), said granite samples were found two years ago during dredging operations in an area known as "Rio Grande Elevation", a mountain range in Brazilian and international waters.
Granite is seen as a continental rock.
"This could be the Brazilian Atlantis. We are almost certain but we must bolster our hypothesis. We will have final (scientific) recognition this year when we conduct drilling in the area to retrieve more samples of these rocks," the G1 news website quoted Ventura as saying.
Initially, the scientists thought they were mistaken, Ventura noted.
But last month, their case was bolstered when a team of Brazilian and Japanese scientists aboard Japan's manned research submersible Shinkai 6500, observed the underwater geological formation located opposite the Brazilian coast, he added.
"We began to see that the area could be a piece of the continent that disappeared into the sea millions of years ago," Ventura said.
Explore further: New tool could bring clearer view of oxygen-minimum oceanic zones