NASA Images Discover Ancient Bridge between India and Sri Lanka
Space images taken by NASA reveal a mysterious ancient bridge in the Palk Strait between India and Sri Lanka. The recently discovered bridge currently named as Adam's Bridge is made of chain of shoals, c.18 mi (30 km) long.The bridge's unique curvature and composition by age reveals that it is man made. The legends as well as Archeological studies reveal that the first signs of human inhabitants in Sri Lanka date back to the a primitive age, about 1,750,000 years ago and the bridge's age is also almost equivalent.
This information is a crucial aspect for an insight into the mysterious legend called Ramayana, which was supposed to have taken place in treta yuga (more than 1,700,000 years ago).
In this epic, there is a mentioning about a bridge, which was built between Rameshwaram (India) and Srilankan coast under the supervision of a dynamic and invincible figure called Rama who is supposed to be the incarnation of the supreme.
This information may not be of much importance to the archeologists who are interested in exploring the origins of man, but it is sure to open the spiritual gates of the people of the world to have come to know an ancient history linked to the Indian mythology.
[Courtesy: NASA Digital Image Collection] [Homepage: http://www.nasa.gov/]

Two more sources:
Sri Lanka History
The first signs of human inhabitants in Sri Lanka date back to the Stone Age, about 1.750.000 million years ago. These people are said to have come from the South of India and reached the Island through a land bridge connecting the Indian subcontinent to Sri Lanka named Adam's Bridge. This is related so in the epic Hindu book of Ramayana.

Adam's Bridge
Rama's Bridge, chain of shoals, c.18 mi (30 km) long, in the Palk Strait between India and Sri Lanka. At high tide it is covered by c. 4 ft (1.2 m) of water. A steamer ferry links Rameswaram, India, with Mannar, Sri Lanka. According to Hindu legend, the bridge was built to transport Rama, hero of the Ramayana, to the island to rescue his wife Sita from the demon king Ravana.

Rama's Bridge
From Wikipedia, the free encyclopedia
Rama's Bridge, Nala's Bridge is a chain of limestone shoals, between the islands of Mannar, near northwestern Sri Lanka, and Rameswaram, off the southeastern coast of India. The bridge is 30 miles (48 km) long and separates the Gulf of Mannar (southwest) from the Palk Strait (northeast). Some of the sandbanks are dry and the sea in the area is very shallow, being only 3 ft to 30 ft (1 m to 10 m) deep. This seriously hinders navigation. It was reportedly passable on foot as late as the 15th century until storms deepened the channel. A ferry links the island and port of Rameswaram in India with Talaimannar in Sri Lanka; the Pamban Bridge links Rameswaram island with mainland India.
The names Rama's Bridge and Nala's Bridge originate in Hindu mythology. According to the Hindu epic Ramayana (Chapter 66, The Great Causeway [1]), the bridge was constructed at Rama's request by his subjects, including the Vanara Sena (army of monkeys), led by Nala, son of the architect-god Visvakarman. The bridge was supported on floating rocks but the gods were said to have later anchored the rocks to the sea bed, thus creating the present chain of rocky shoals. It was said to have helped Rama to reach Sri Lanka to rescue Sita from a monster called Ravana, who was then the ruler of Lanka.
Some Hindu groups claim that the bridge is evidence that events narrated in the Ramayana epic actually took place and cite NASA's imagery of it as proof of their claims. NASA has distanced itself from such claims:
"The images [...] may be ours, but their interpretation is certainly not ours. [...] Remote sensing images or photographs from orbit cannot provide direct information about the origin or age of a chain of islands, and certainly cannot determine whether humans were involved in producing any of the patterns seen."
Archeological studies of the bridge are ongoing, and some archeologists claim to have found evidence suggesting that the bridge is man-made. For instance, some researchers from Bharathidasan University, Tiruchirappalli, announced that the "bridge" is only 3,500 years old.
Sea levels rose about 10 or 20 metres in the 6th millennium BCE to reach levels similar to today, so in 6000 BCE the bridge would have been an isthmus situated above sea level. As such, it almost certainly would have been a viable route for humans to have reached Sri Lanka by dry land.
Recently the Government of India has approved a multi-million dollar Sethusamudram Shipping Canal Project that aims to create a ship channel across the Palk Strait. The plan is to dredge the shallow ocean floor near the Dhanushkodi end of the Rama's bridge to create enough leeway allowing ships to pass through the channel instead of having to go around the island of Sri Lanka. It is expected to save nearly 30 hours' shipping time by cutting over 400 km off the voyage. However, efforts to conserve the heritage of the bridge has been initiated under the Ram Karmabhoomi movement.

Rama's/Adam's Bridge as seen from the air