eog utilized average prices per acre from comparable market transactions and estimated discounted cash flows as the basis for determining the fair value of unproved and proved properties , respectively , received in non-cash property exchanges .see note 10 .fair value of debt .at december 31 , 2018 and 2017 , respectively , eog had outstanding $ 6040 million and $ 6390 million aggregate principal amount of senior notes , which had estimated fair values of approximately $ 6027 million and $ 6602 million , respectively .the estimated fair value of debt was based upon quoted market prices and , where such prices were not available , other observable ( level 2 ) inputs regarding interest rates available to eog at year-end .14 .accounting for certain long-lived assets eog reviews its proved oil and gas properties for impairment purposes by comparing the expected undiscounted future cash flows at a depreciation , depletion and amortization group level to the unamortized capitalized cost of the asset .the carrying values for assets determined to be impaired were adjusted to estimated fair value using the income approach described in the fair value measurement topic of the asc .in certain instances , eog utilizes accepted offers from third-party purchasers as the basis for determining fair value .during 2018 , proved oil and gas properties with a carrying amount of $ 139 million were written down to their fair value of $ 18 million , resulting in pretax impairment charges of $ 121 million .during 2017 , proved oil and gas properties with a carrying amount of $ 370 million were written down to their fair value of $ 146 million , resulting in pretax impairment charges of $ 224 million .impairments in 2018 , 2017 and 2016 included domestic legacy natural gas assets .amortization and impairments of unproved oil and gas property costs , including amortization of capitalized interest , were $ 173 million , $ 211 million and $ 291 million during 2018 , 2017 and 2016 , respectively .15 .asset retirement obligations the following table presents the reconciliation of the beginning and ending aggregate carrying amounts of short-term and long-term legal obligations associated with the retirement of property , plant and equipment for the years ended december 31 , 2018 and 2017 ( in thousands ) : .
[['', '2018', '2017'], ['carrying amount at beginning of period', '$ 946848', '$ 912926'], ['liabilities incurred', '79057', '54764'], ['liabilities settled ( 1 )', '-70829 ( 70829 )', '-61871 ( 61871 )'], ['accretion', '36622', '34708'], ['revisions', '-38932 ( 38932 )', '-9818 ( 9818 )'], ['foreign currency translations', '1611', '16139'], ['carrying amount at end of period', '$ 954377', '$ 946848'], ['current portion', '$ 26214', '$ 19259'], ['noncurrent portion', '$ 928163', '$ 927589']]
( 1 ) includes settlements related to asset sales .the current and noncurrent portions of eog's asset retirement obligations are included in current liabilities - other and other liabilities , respectively , on the consolidated balance sheets. .

Question: what is the percentage of the carrying amount of proved oil and gas properties concerning the total carrying amount in 2017?
Answer: 40.53%
Explanation: it is the carrying amount of proved oil and gas properties in millions divided by the total carrying amount , also in millions , then turned into a percentage .