https://imgur.com/a/ZmzVDci

Hello! Husband and I just purchased a house and are pulling up the carpet to have the hardwood underneath instead. In one room only, we found this yellow/tan layer under the carpet and pad. It has a leaf-like tread and mesh on both sides and doesn’t seem fibrous, more like caked mud. Any thoughts on what this might be?

House was built in the 60s but the carpet seems in really good shape to be that old so we’re hoping it’s not dangerous. Thank you!